Abstract

This literature review examines the relation between Asthma and Nitrogen Oxide. It will serve as preliminary information for our group’s air pollution campaign in New York City. Asthma is the most common non communicable disease among children (World Health Organization, 2017). Nitrogen Oxide pollution is a particulate matter that impacts respiratory conditions (GreenFacts, 2019). The relation between Asthma and Nitrogen Oxide is kept independent of location due to this literature review decision of analyzing 4 studies from 4 regions: China, Los Angeles, Mexico, and New York City. To explore the relation between Asthma and Nitrogen Oxide, this literature review will examine the methodology, participants, and results of 16 peer-reviewed journals from 2013 to 2019. Examining the methodology will describe the author’s actions to address the research question, and logic behind their procedure to evaluate the studies overall validity. The results are examined to define the relation between Asthma and Nitrogen Oxide. Reviewing the participants in the research will help us evaluate the relevance of the study’s results to other groups of people.

 Introduction

One of the biggest problem of the 21^st Century: Air Pollution. Air pollution is a mixture of particulate matter and gases in the air (Medline Plus, 2018). Consumer products that either produce or expend energy, such as cars, are the main sources of the pollution that researchers have concluded are to blame for numerous negative health effects (National Institute of Environmental Health Sciences, 2019). Our group’s focus will be on a particular air pollutant and its effect on a particular disease: the effect of nitrogen oxide on Asthma. Nitrogen oxides are a group of seven gases and compounds composed of nitrogen and oxygen. Nitrogen oxides are emitted by vehicle exhaust. Nitrogen is emitted during fuel combustion which then combines with oxygen in the air to produce nitric oxide. It can then further combine with oxygen to produce nitrogen dioxide (U.S National Library of Medicine, 2017). Although nitric acid is not hazardous to health nitrogen dioxide is, and that is a major reason for the disproportionately high concentrations of NO2in major cities, and a reason that issue is so dire. Other than transportation, NO2is emitted from industrial processes, energy use in the industry, and commercial uses, making it one of the most difficult air pollutants to control the use of (Icopal, 2015).

Asthma is a chronic respiratory disease that is incurable. It is composed of inflammation, which is swelling and mucus in the airways, and constriction in the airways. Some symptoms of Asthma include wheezing, coughing, chest tightness and shortness of breath (National Heart, Lung, and Blood Institute, n.d). As we have seen through our research, the high emissions have had an immense impact on the lives of those living in urban areas, especially in the context of asthma and asthma related symptoms. The proportion of Asthma is substantially higher in urban and socioeconomically disadvantaged communities. Members of these communities are more likely to have Asthma, have more asthmatic symptoms, higher hospitalization, and a higher death rate due to Asthma (Kant, 2013 p. 446). In addition, Asthma is the most common non communicable disease among children (World Health Organization, 2017).

Additionally, Asthma is becoming an increasingly economic problem in the US. The CDC states that the cost of asthma is $80 billion per year (The American Journal of Managed Care [AJMC], 2018). The World Health Organization( [WHO], 2017) has estimated that Asthma has caused 385,000 deaths in 2015.  Through scientific studies our group intends to find if there is a correlation between Asthma and Nitrogen oxide and if there are successful methods to reduce density of nitrogen oxide in cities by parsing through 16 studies associating Nitrogen Oxides with Asthma.

Methodology

The team’s literature review began by conducting broad searches of air pollutants and their effects on the incidence of asthma. We found studies that monitored air pollutants such as SO2, NO2, PM2.5, and PM10, but ultimately decided to select NO2 because it had the strongest correlation to asthmatic symptoms, and is highly concentrated in urban areas due to the number of cars. The members of the team then researched studies from four different places around the globe, Mexico, China, New York City, and Los Angeles, to compile an array of data to be able to make a broad connection between asthma and NO2. Los Angeles was selected because is the most polluted city in the United States (Most Polluted Cities, 2017). New York City is the most densely populated city in the United States, and the city in which we live, so we can make a specific connection to a community being affected by high nitrogen oxide concentrations. We then, due solely to the number of relevant studies available, decided to do different cities within China and Mexico rather than focusing on a specific city. China has a population of over a billion people, and it is the most industrialized country in the world (Kiprop, 2018). Due to the industrialization the cities of China have some of the highest concentration of air pollutants in the world. Likewise, Mexico city with a population of 20 million people has some of the most polluted air in the world (Schachar, 2018).

Members of the team used Academic Search Complete, Google Scholars, and ScienceDirect to ensure that the studies were peer reviewed and provided reliable information. A year range of 2013-2019 was used when selecting studies because new advances are constantly being made in the medical field and it is important to have research from the most recent studies. The age of the studies is also extremely important for our topic because a major portion of our air pollutant NO2in the air is emitted from cars, and the number of cars, and industrialization in general,  has dramatically increased in all of our locations over the past decade. Using data on concentrations of air pollutants from more than five years ago would not paint an accurate representation of the current situation regarding air quality in different urban areas.

Using the databases our team utilized boolean phrases in order to narrow our searches and find the most relevant articles. Prior to narrowing our searches using the terms, our searches would yield hundreds to thousands of studies to read and sort through, many of which were not relevant to the direction we wanted our research to go in. After utilizing our key words we were able to more effectively research. Some examples of the keywords used were asthma, nitrogen oxides, air pollution, and NO2. Each individual member of the team then narrowed the search further by including our locations in the search. On some occasions, after finding a suitable source, group members were able to use keywords from that study to find other studies with similar subject matter. For example, one of the key words in a Chinese study was “respiratory problems”. The group was then able to utilize this keyword to find similar studies. This proved to be very helpful and allowed for an easy search process.

The original intent of our research was to use the studies to find the relationship between NO2 exposure and the onset of childhood asthma. However, while researching some members of the group were not able to find an adequate number of relevant, and reliable studies that only focused on children, so as a group we decided to broaden our topic to include adults. Our group has research of air pollution’s effect on individuals ranging from in utero to adults. With this large range we as a group were able to analyze the difference in an individual’s susceptibility to asthmatic symptoms at different stages of life, and at different stages of immune and respiratory development. This final decision solidified our research topic and allowed us to begin the process of writing the literature review.

China

China is the most industrialized and populated country in the world, making it a prime location for studies on air pollution. Over the past 15-20 years China has seen a surge in number of cars on the roads greatly, increasing the NO emissions in the air in which NO2 is derived from (Zhang, Ni, Bai, Cheng, Zhang, et al., 2019, p. 510). Using studies from China to compare the effect of NO2 on asthma to New York City and other large cities is appropriate because urban areas of China resemble New York City in many ways including the proximity of industrialization, the number of cars on the roads, and the highly concentrated population living in small areas. When researching, studies were selected that focused on different stages of childhood because there is a large difference developmentally between a child that is two, and someone that is seventeen, and to fully understand the connection between air pollutants and childhood asthma, age is an important factor. By researching studies that ranged from prenatal pregnancy all the way to ~17.5 years, the ways in which NO2 affected asthmatic symptoms in various stages of respiratory and immune development was observed. This proved to be important in determining whether NO2 directly causes asthma or if it just heightens respiratory symptoms.

        A child’s exposure to air pollutants begins before they are born. A study in Changsha, China, the capital of the Hunan Province, was conducted to determine the effects that air pollution has on a baby while in utero. Lung development begins in fetuses when they are around three to four weeks old, and the structural development and functional maturation continues into early adulthood, making a mother’s exposure to air pollution critical in influencing whether or not the child have respiratory problems (He, Huang, Kwok, Leung, Hui, et al., 2019, p. 444).  Exposure to air pollutants while pregnant has been linked to a greater chance of adverse outcomes including allergic diseases such as asthma. The results of the survey distributed to 4988 preschool aged children during the study showed that there was a positive correlation between a mother’s exposure to air pollutants, especially NO2, and the incidence of the child having an allergic disease. Asthma had an incidence of 6.8%. These results imply the detrimental effects that air pollution can have on children by showing that children do not have to be directly exposed to the pollutants to suffer the consequences, but rather can start developing these conditions in the womb. The period in utero is critical for the development of the respiratory system, especially during the second and third trimester where the airways develop rapidly. This means that toxic pollutants can have major effects on the child’s ability to fight infections, and develop a healthy respiratory system. The thoroughness of the way this study was conducted leads on to believe the results are valid. The research team used a large sample size and was very thorough in recording the air pollutants on a daily occurrence throughout the mother’s pregnancies, as well as breaking it down into trimesters in order to connect the NO2 concentrations to abnormal lung development throughout the trimesters (Deng, Lu, Li, Sundell, & Norback, 2016, p. 119).  

        The respiratory symptoms that come as a result of air pollutants are sometimes confused with the actual disease of asthma although they can exist independently. A study conducted in seven northeastern cities of China explored this concept. The study consisted of children from 25 elementary schools who lived within a mile of their elementary school, and averaged 9.5 years old. They were given questionnaires inquiring about the respiratory issues and symptoms they suffered from, possibly due to air pollution. They monitored persistent cough, persistent phlegm, current asthma, and current wheeze. This study looked at air pollutants, proximity to major roads or smoke stacks as well as the indoor factors such as pets and cooking methods. The study concluded that all of these factors, but especially distance to major roads and smoke stacks, were associated with respiratory disease symptoms. The distance to roads was so crucial because it was telling of how much nitrogen oxides as well as other air pollutants emitted from cars the children were exposed to on a daily basis. Ambient air pollution was associated with a prevalence of asthma related symptoms. It is important to note that this study determined that they lacked sufficient evidence to directly link air pollution to asthma. However, they found sufficient evidence relating air pollution to allergic symptoms as the study found that of the children from the 25 elementary schools in urban areas surveyed 8.5% reported a persistent cough, 6.3% persistent phlegm, and 5.1% current wheeze (Liu, Zhao, Liu, Liu, Sun, et al., 2014, p. 497). The fact that the scientists conducted the surveys in 25 elementary schools and were able to come to a common consensus leaves one to believe that the results are reliable.

        Another study in China was composed of the oldest children in the 0-18 age range and conducted in Hong Kong. This study evaluated lung function of a group of 8,327 ~17.5 year olds known as the Hong Kong “Children of 1997” cohort, and the effect that air exposure had on it. The subjects of the study were first selected at birth and initially evaluated, answered a health update questionnaire eight years later, and then finally about seventeen years later were reevaluated for lung function. The Environmental Protection Department provided records of monthly concentrations of air pollutants including NO2 throughout the different stages of the subject’s childhoods. When reevaluated the functionality of the lungs was determined using two methods. First in terms of forced vital capacity which is the amount of air that can be exhaled after taking the deepest breath possible, and forced expiratory volume which is how much air can be exhaled in a given time period (FEV1 and FVC, 2018). These tests allowed for researchers to check the functionality of the lungs and determine other respiratory issues and symptoms that the subjects may have without necessarily being connected to the asthma disease. Final analysis showed that 10.1% of the girls and 14.7% of the boys described history of asthma and wheezing . Higher exposure to NO2 and NO pollutants during early childhood led to lower lung functionality in the forced vital capacity and forced expiratory volume tests. Nitrogen oxides had the strongest correlation to reduced lung function and an increase in incidences to wheezing and other symptoms of lung diseases but there was no direct correlation between air pollution and asthma. However, this study did show that prenatal, infancy and toddlerhood is the most critical period of development for lung function, and that NO2 is related to airway obstruction later in life. Higher exposure to NO2 showed poorer lung function at ~17.5 years. However, if the study had utilized a control group, perhaps children living in the rural areas where there is a substantial decrease in air pollution, it would allow for comparisons in the incidence of asthma and provide what the normal/average lung function for a child of this age should be in terms of forced vital capacity and forced expiratory volume. Other than that, the large sample size of the study and the monthly records from the Chinese Environmental Protection Department lead our group to believe that this study yielded viable results (He et al., 2019, p. 444).

        The final study we looked at collected data from children of all ages of the range (0 to 18 years old) in Hefei City, China. The study monitored daily admissions for childhood asthma at Anhui Provincial Children’s Hospital, and monitored the concentrations of air pollutants including nitrogen dioxide. The study found that asthma-based admissions increased with the concentrations of all the pollutants studied, but the strongest correlation was with NO2. They also found that grade school children, ages 7 to 18, were affected by the pollutants more than the preschool aged children most likely because they spend more time outside doing activities, increasing their exposure to the pollutants . This study looking at short term effects concluded that an increase in the level of air pollutants lead to an increase in hospital admissions, however, this study did not explore the idea that air pollutants such as NO2 can cause asthma in children. Similar to the past two articles this study showed that an increase in air pollutants leads to increased symptoms of asthma, hence the increased admissions, but is not directly linked to the disease itself (Zhang et al., 2019, p. 510). Unlike the other studies from China, this study took a more broad look at the incidence of asthma and asthmatic symptoms in all children instead of a specific age range. Due to the complexities and differences in respiratory and immune reactions throughout the different stages of development in childhood I do not think a wide study such as this is ideal. Perhaps for adults it is, but for children any connections made between asthma and air pollutants should be made considering the specific stage of childhood.

        After reading through all of the studies the only case that determined a direct link between the air pollution and asthma was the study conducted on air pollution exposure of mothers during pregnancy. The other studies did not find a strong enough correlation but rather suggested the air pollution increases the prevalence of symptoms of respiratory diseases such as wheezing, coughing, and reduced lung function. This information solidifies the idea that the most important period of respiratory and immune system development takes place in utero, hence why an increased exposure to air pollutants such as NO2 would lead to asthma more often than exposure later in childhood. Although not all of the studies found a direct link between the incidence of asthma and NO2exposure, they all stress the consequences of exposure to air pollutants, and provide context for why changes must be made to ensure health respiratory function in children.

Los Ángeles

Los Angeles has been known for years as the most air polluted city in the US, and New York City is in the Top 10. These two cities can really be said to be the urban capitals of the United States, meaning that in them air pollution and asthma go hand in hand. In one study, “Inducible Nitric Oxide Synthase Promoter Haplotypes and Residential Traffic-Related Air Pollution Jointly Influence Exhaled Nitric Oxide Level in Children”, whose topic is geared to finding if specific promoters in nitric oxide synthase can affect the concentration of nitric oxide in exhaled air (FeNO) tries to see how it is also associated with asthma and lung function in children (Salam, Eckel, Gauderman, & Gilliland, 2015). The researchers hypothesized that the effects of a nitric oxide synthase promoter would influence the relationship between the road length around the homes of the subjects and FeNO. They also hypothesized that this synthase promoter and length of road traffic on nitric oxide would vary asthma levels in children. To begin this research, they went to kindergarten and first grade students from 12 communities in Southern California. The demographic they chose for race was a total of 2457  Hispanic and non-Hispanic white children. Most of these students already had respiratory problems, but in their final analysis they made sure not to include children who had previously been diagnosed with asthma and those who had been exposed to secondhand smoke. This exclusion variables make sense because they are two factors that could be disproportionately influential in the analysis of FeNO in these children. They decide to measure the children’s exposure to nitric oxide in length of roads around their address in 50m, 100m, and 200m buffers. In their results they discovered that “Children with 2 copies of the H1 haplotype who had fewer roads within 100m and 200m buffer around their homes had significantly lower FeNO compared to children who had similar exposure but no copies of the H1 haplotype (Fig 1 and Table 5). This protective effect of H1 haplotype on FeNO was abrogated in children who lived in homes surrounded by more roads”( Salam et al., 2015). In plain words, they saw that when the children had fewer roads in their buffer area, they had lower FeNO compared to when they had more roads surrounding their homes and the haplotype seemed to be nonexistent. Their final conclusion reiterated the fact that FeNO is a marker of airway inflammation because of the pollutant of nitric oxide. They had tried to understand whether the promoter would help in high level of traffic exposure, but they found that, “…children may not benefit from having a protective DNA sequence variants in NOS2 promoter…” therefore finalizing in the idea that there needs to be planning in transportation in residential areas so “traffic-related exposures could be reduced to protect children’s respiratory health” ( Salam et al., 2015).

Los Ángeles being an urban city is exposed to air pollutants at almost all times because of heavy traffic they have. The study, “Asthma Morbidity and Ambient Air Pollution: Effect Modification” by Residential Traffic-Related Air Pollution similarly decided to focus on children and the respiratory effects of traffic-related pollution. They hypothesized that the “relationship between daily ambient air pollution and daily hospital morbidity for asthma in individual children will be enhanced by higher chronic exposures to traffic-related air pollution near the subjects’ homes” (Delfino, Wu, Tjoa, Gullesserian, Nickerson, & Gillen, 2014). Thus, they were trying to relate the morbidity rates with the traffic near the subjects’ homes. The method that they used to find the relation between the hospital morbidity and how it would be enhanced by traffic related air pollution was to go to two hospitals, “Children’s Hospital of Orange County and University of California Irvine Medical Center in Orange County, California (Delfino et al., 2014, pp. 48-57).”, and take the records for subjects ages 0-18 that had a hospital encounter with a primary diagnosis of asthma. They took the locations of where each one lived and tracked the air pollution and each of the pollutants within 500m buffer area of the address of the subject. They decided to also analyze how the specific pollutants acted in different seasons. Their results found “positive associations”of air pollution with hospital morbidity. For NO2, they found the associations to be stronger in the cooler seasons. They also were able to relate the same contribution as the previous study which explained that asthma increased from higher levels of traffic sources.  They state that, “associations reported in the time series literature may underestimate effects of ambient air pollutants on asthma morbidity for pediatric populations so exposed as a result of acutely increased vulnerability or chronically increased susceptibility.” (Delfino et al., 2014). This is further explaining how pediatric populations are increasingly vulnerable to the effects of the concentration of pollutants, such as NO2, in their bodies.

To further the investigation on the air pollution in Los Angeles and how it affects asthma specifically in children, a next study, “Traffic-related air pollution and alveolar nitric oxide in southern California children”, helped to further understand this problem (Eckel, Zhang, Habre, Rappaport, Linn, Berhane, Gilliland, 2016), Traffic-related air pollution (TRAP) is a “complex mixture of primary particulate matter and gaseous pollutants.” that has adverse respiratory effects. The focus for this study would be on Nitric Oxide, a pollutant that is present both indoors and outdoors. NO can be rapidly oxidised and turned into Nitrogen Dioxide once emitted (Eckel, Zhang, Habre, Rappaport, Linn, Berhane, Gilliland, 2016). The hypothesis of this study is,  “investigate the association between short-term exposure to TRAP and localised lower respiratory tract inflammation ” (Eckel et al., 2016).  Their methodology included children from the CHS cohort that had been recruited when they were in kindergarten and first grade in Southern California. From these they chose 1635 children from 8 communities that had participated in the first year of FeNO assessment. They used FeNO analysers to measure indoor NO hourly, in empty schoolrooms. The children participated in breathing tests which measured the amount of FeNO that was being released every exhale.  They related indoor NO exposure to the FeNO measurements and adjusting potential cofounders of demographics. The participants that they ended up measuring were 12 to 15 and “more than half identified as Hispanic white (58.2%); most had some history of rhinitis (38.1% not current and 31.5% current); and 321 (19.6%) reported a physician diagnosis of asthma, of whom 48 reported taking inhaled corticosteroid medication in the past 12 months.”(Eckel et al., 2016). These are the children who were part of the same cohort group in 2003 and now are being tested for this specific measuring.

They found that there was strong evidence for positive association of indoor exposures to TRAP with FeNO in schoolchildren,  FeNO was higher on days when the outdoor NO was high(Eckel et al., 2016). To measure the FeNO they had, they would do “online”tests with a specific research person and “offline” tests that would be given to the actual subjects to be done on their own. They finally concluded that TRAP exposure was associated with exhaled Nitric oxide in schoolchildren. For future studies they wanted to measure  the exposure even more specifically and study a larger sample that already had asthma.

The final study analyzed for the investigation of air pollution in Los Angeles was, Associations of children’s lung function with ambient air pollution: joint effects of regional and near-roadway pollutants. The main question of this study was, “Do residential near-roadway and regional air pollution cause reduced lung function?” (Urman, McConnell, Islam, Avol, Lurmann, Vora & Gauderman, 2013). They were trying to see associations with traffic proximity measures and how this affected children’s lung functions. They checked the exposures both at their homes and schools. Urman et al. (2013) expressed the “predicted lung function in these different environments as percentages relative to those in the cleanest environment (low regional and low NRAP).” the lowest of pollution in these traffic- filled areas. The mean age they used was 11.2, “…40% of the participants were white and 57% were of Hispanic ethnicity (table 1). Household income less than $30,000 and parental education less than high school were common…”. These were the main demographics from the results they received and they further found that, “Although close proximity to a major road was negatively associated with each measure of lung function, these associations were not statistically significant.”  (Urman et al., 2013).They thought that maybe background pollutants might have changed the lung function deficits by increasing them in the communities where they had found the high pollutants, but none of them significantly changed the association between the NRAP and the lung functions.

Finally, their results did indicate that exposure to NRAP would adversely affect the childhood lung function (Urman et al., 2013). It was also consistent with the relationship of distance to the freeway. “Furthermore, the strong association between exposure and lung function in non-asthmatic children suggests that traffic-related pollution did not affect only a sensitive subgroup but rather has a potential impact on all children.” (Urman et al., 2013). This last study reiterated that the childhood lung function could potentially and probably affect the lung function of children even as they go into adulthood.

Mexico

Before analyzing studies that go into detail about the effects of Nitrogen oxide and public policies to limit pollution in Mexico, it is important to first understand how prevalent Nitrogen Oxide is in metropolitan areas. Authors of the study titled “Statistical persistence of air pollutants in Mexico City” tackled the task of analyzing historical data of pollution in the city. They were precise in defining their study area: Downtown Mexico City, 19° 25′58.09′′ N, 99° 07′59.68′′ W (Meraz, Rodriguez, Femat, Echeverria & Alvarez-Ramirez, 2015, pg. 203). They also decided to explicitly state the deterministic (not random) and stochastic (random) components of the study and provide a link to open data for the reader to analyze: http://www.aire.cdmx.gob.mx/default.php (Meraz et al., 2015, pg. 204). They used Rescaled Range analysis that is explained to be a way to prevent random events from being included in the relevant and consistent data. The results of the study that are relevant to us found that there is a high persistence of ozone concentration which is associated with low persistence of nitrogen oxide concentration (Meraz et al., p. 214). From how the authors explained it, this means that the concentration of Nitrogen dioxide is not constant over time. Although they did not have a conclusion, they claimed that R/S analysis can be considered as “a complementary tool for monitoring the probable impact of air-pollution control measures in Mexico City” (Meraz et al., 2015, pg. 216). Their results can be interpreted as proof that human actions can affect the concentration of nitrogen dioxide in Mexico city.

Establishing that human intervention can affect the levels of air pollution, the following study that was analyzed “Income and Air Quality in Cities: Does a Kuznets Curve Exist for Transport Emissions in the Valley of Mexico’s Metropolitan Area?” by Vanessa Perez- Cirera, Elisa Schmelkes, Oliver Lopez-Corona, Francisco Carrera, Ana Paula, and Graciela Teruel (2017) discussed the relationship between air pollution and income wealth. Although they also focused on how the density of pollution was related to transport and its impact on human health. They determined if there was a strong linear, quadratic or cubic relationship between income and Carbon monoxide, nitrogen oxides, and carbon dioxides (a Kuznet curve). A Kuznet curve, in relation to the environment, is a theory that as the income per capita increases, pollution will also increase, but after the income per capita increases beyond a critical point, pollution will decrease. The graph of the Kuznet curve looks like an inverted U. In short, the authors wanted only to see if people in different income responded to air pollution differently. They claim that people of high levels of income did not consider the social cost of polluting (Perez-Cirera et al., 2016, pg. 746).

In the next paper I studied titled “ Evaluation of the Impact of Bus Rapid Transit on Air Pollution in Mexico City” focused on the before and after the implantation of Bus Rapid Transit in Mexico City (Bel & Holst, 2018). The Bus Rapid Transit is a bus service that has similar performance to that of a subway. They emphasize the ease of implementation, the relatively low initial investments cost, and flexibility of the Bus Rapid Transit, almost to the point of advertising it  (Bel & Holst, 2018, pg. 209). Air pollutants this study considered are carbon monoxide (CO), nitrogen oxides, and particulate matter of less than particulate matter (PM) of 10 μm(Bel & Holst, 2018, pg. 209). According to the authors, nitrogen dioxide is more than 4 times smaller than a single strand of hair (50 μm). Emphasizing the author’s assertion that PM of 10 and 15 μm is linked aggravating asthmatic conditions and Nitrogen oxides effect on the respiratory system (Bel & Holst, 2018, pg. 210).

One of the important takeaways from this study is that they studied if public bus transportation reduced the quantity of pollutants that inhabitants in Mexico city are exposed to by comparing other studies done by others. Overall, there was a reduction of pollutants in the air due to the implantation of public bus transportation. Bel & Holst provided backed their claims through previous studies such as on by Chavez-Baeza and Sheinbaum-Pardo whose work in Mexico City from 1990-2008  found that there was a reduction of 15.4% of NOx after the implementation of public buses (Bel & Holst, 2018, pg. 211). The authors also conclude that bus transportation is a valid alternative to reduce quantity of pollutants.

Bel & Holst (2018) provided to the reader the equation they used to interpret their data. This equation was derived from the difference-in-difference method (Bel & Holst, 2018, pg 213). They explain that it is basically having a control group (stations located between 10 and 30 km away from the area through which the bus passes) and an intervention group (stations within a radius o 10 km around the bus line) and measuring the difference the implantation of public bus had on the intervention group. In short, they saw a reduction of 4.7 %and 6.5% of NOx. Their conclusion ended off by suggesting that other cities similar in size to Mexico City will also have reduction in air pollution emissions if they implemented better public transportation infrastructure (Bel & Holst, 2018, pg 218).

The last study was not in Mexico, but in the border area, and furthered encouragement to limit emissions of Nitrogen oxide pollutants. The authors of the journal titled “Asthma Prevalence and School-Related Hazardous Air Pollutants in the US- Mexico border Area” clearly projected that the reason their research was important is because the severity in which asthma is present among children (Carrillo, Patron, Johnson, Zhong, Lucio & Xu, 2018). Their objective was to find to see if there is a relationship between air pollution and quantity of asthma in children. The authors carried a quantitative cross-sectional study “combining a school-based asthma screening survey across 198 schools in Hidalgo County, Texas”. Translated to plain English, they simply did a study across an area in which the people lived under the same conditions with only 1 or 2 key differences. They then studied if the differences led to an increase of asthma among children.  The two differences of study were hazardous air pollutants (HAPS) and socioeconomic status (SES), concerning with the interaction between social and economic factors (Carrillo, 2018, pg. 42).

One of the potential faults of this study was covered extensively under section 2.2 Asthma screening questionnaire and asthma status ascertainment, that is, the accuracy of diagnosis of asthma among children in the Hidalgo County. They were able to screen 2930 students from 198 school in the County using validated questionnaire developed by the American College of Asthma, Allergy, wand Immunology. The question they asked for diagnosis are given in Table 1(Carrillo, 2018, pg. 43). Their results were surprising. As the authors show in Table 2, children between the ages of 14 and 18 had a prevalence of asthma of 16.67%, higher than the United States average of 10% (Carrillo, 2018, pg. 46).

Their results showed that is no correlation between SES and asthma prevalence in the Hidalgo County. Additionally, they suggest that there is an impact of HAPs on the health of children in the Hidalgo County. Interestingly, the authors have reached the same conclusion as the studies in China: there is no correlation between air pollution and asthma prevalence, HAPS only exacerbate asthma symptoms. They also suggest that further study on the relationship on air pollution and Asthma.

New York City

New York is the one the most privileged cities in the world, and with that responsibly also comes a negative impact on the environment and the citizens that live there due to air pollution.  The study “Residential Demand Response Reduces Air Pollutant Emissions on Peak Electricity Demand Days in New York City” sheds some light on how present Nitrogen Oxide is in NYC. The study explains that during “periods of peak electricity demand… older combustion turbine [power generators] utilized…”(Gilbreth & Powers, 2013, pg. 460). The reader is concisely told that the reason old turbines are bad is because they expose nearby residents to hazardous air pollutants (such as NOx). Gilbreth & Powers (2013) hypothesized that if residential consumers were charged at a higher rate during peak demands, the older combustion turbines will generate less electricity. They thoroughly explained that the simulator to use to “quantify changes in generator dispatch” was the General Electric Multi-Area Production Simulation Software (Gilbreth & Powers, 2013, pg. 461). They then went in to detail on simulating residential demand response, load alteration and the economic impact of air pollution.

Gilbreth & Powers (2013) displayed authenticity by discussing the uncertainty in their measurements under results. Their results showed that dynamic tariffs during peak hours did in fact change the residential consumption of electricity. There was a reduction of 1.4 metric tons of NOx, although it was only 3.1% of the target for NOx emission reduction (Gilbreth & Powers, 2013, pg. 461). What is the most important takeaway from this study that relates to our topic is that New York State set to see a reduction of 41 metric tons of NOX every day. According to this study, that much of a reduction can save $50,710-87,590 every day (Gilbreth & Powers, 2013, pg. 465). This can provide a powerful incentive for cities that are looking at air pollution from an economic standpoint.

It is estimated that of all the time spent indoors by individuals, they spend ∼90% of it in close proximity to gaseous air pollutants. When considering the effect that air pollutants must have on the respiratory of children, it is a common thought that the main source of air pollutants such as NO2 comes from exposure outside from cars and factories, however this study evaluates indoor contributions that are often overlooked but equally as important. A particular study looked at three air pollutants particulate matter, ozone, and nitrogen dioxide, which is the focus of our study.  Children from the pulmonary clinic, asthma clinic, and emergency room from Mount Sinai Hospital who lived in the South Bronx and East Harlem were observed for two years during the warm and cold season. Inspecting was initially planned to occur in the winter and summer seasons only; however, a few sessions ran into the spring and fall, separately. These areas are among the most diverse and polluted areas in any of the boroughs of New York. Outdoor concentrations of air pollutants were measured at a central site which was located on the roof of a City College of New York building. The indoor conditions, meaning the test subject’s residences, were monitored for an average of fourteen days  by a monitoring machine that was placed in the living room of the subject’s houses. Upon installation a quick survey was also given to the parents or guardians of the child which gathered information about other factors that could influence the results such as if there were any smokers in the house, how many people lived there, were vacuums or candles used, and has anyone cooked on a stove recently. Children who lived in houses where people smoked were omitted from this study so that the results pertaining to asthma would not be skewed by the effects of secondhand smoke, but come from other sources of indoor pollution (Habre, Coull, Moshier, Godbold, Grunin, et al, 2014, pg. 274).

The results of this study interestingly found that for fine particulate matter the weekly indoor concentrations actually had a higher average than the outdoor concentrations, revealing that it is equally as important to pay attention to indoor sources of gaseous air pollution as well as outdoor sources. As far as NO2, the focus of our study, it was concluded that cooking and the use of stoves had the largest impact on NO2 concentrations. When the initial survey was given the question “did you fry, bake, or sautee recently?” was directly associated with NO2 concentrations. In one specific instance of the study, a family that answered yes to this question saw a 1.44-p.p.b (parts per billion) increase in the concentration of indoor NO2. This relationship is extremely important to note because as this study described, the concentrations of air pollutants, and specifically NO2, have been found to be linked to asthma and asthmatic symptoms. The indoor emission rate of NO2 exceeded the removal rate of the pollutant by reactions with other surfaces or air exchange. This statistic is alarming in the context of asthma because it shows that NO2 is essentially not being degraded or filtered out in a sufficient rate, meaning that the pollutants is always lingering both indoors and outdoors, affecting the efficiency of the respiratory system especially in children. Although it is almost impossible to rid ourselves from this exposure because stoves are necessary, there are other less harmful methods of cooking. This also emphasizes the importance of decreasing outdoor exposure to the pollutant (Habre, et al., 2014, pg. 280).

A source of error that could have produced inaccurate results is the fact that the monitoring of the concentrations of air pollutants that were planned to be completed in the warm and cold seasons ran overtime into the fall and spring. The temperature, and weather in general have a substantial impact on asthmatic symptoms, so the fact that data was compared between different children in different households, but were not taken during the same time raises a doubt in the accuracy of the results. The sample of this study was also relatively small, with only 37 participants throughout the two locations. This small size does not provide as much diversity in households as there could have been. Although not mentioned in the study, different sizes and styles of home can either allow for better or worse ventilation of the air pollutants. Using a larger group of individuals would have been beneficial because more types of residences would have been accounted for, so it would not be considered as a source of error in monitoring the indoor pollutants in the asthmatic children’s homes. Other than these two factors the manner in which the study was conducted led us to believe that the results were valid, and represented correctly the environment in  which many New York City residents live in.

Another study that correlates with the concept of both indoor and outdoor pollutant emissions was a study that was conducted to monitor air pollution and emergency department visits due to asthma in New York. The objective of this study was to identify air pollutants that increased the risk of asthma related emergency department visits during in an extremely polluted area due to emissions from factories and vehicles. Daily concentrations of ambient air pollution were monitored by the Environmental Protection Agency as well as the emergency department visits from the Statewide Planning and Research Cooperative System. Weather factors including temperature, wind speed, and average humidity were also noted (Castner, Guo, & Yin, 2017).

At the completion of the study a total of 76,651 emergency department visits were recorded over 2192 days producing an average of 35 visits per day with the range being 11 to 20. A majority of the emergency department visits had the first diagnosis code as a ill-defined condition such as shortness of breath, wheezing, or cough, with the second and third diagnosis code being asthma. There was a positive correlation amongst the air pollutants such as ozone, CO, and NO2. A staggering conclusion was met that found that a 9.24 p.p.b. increase in NO2 was associated with a 11.6% increase in asthma related emergency department visits during the month of June. However, only there was only a 3.3% increase in asthma related emergency departments in the months of January-March, and July-October. The study intended on identifying which air pollutants increased the risk of asthma related emergency room visits, but in the end after six years of studies the team was not able to see a clear trend by specific air pollutant, but rather only in the months/seasons. There was no major change in the frequency of emergency department visits that could be connected to the prevalence of certain air pollutants. However, all of the air pollutants had a positive association during the month of June. Although this study was unable to determine whether or not these air pollutants caused asthma, they were able to determine the times of the year when the pollutants have the most effect impact in causing asthmatic symptoms. As the results showed, a majority of the emergency department visits were for ill-defined conditions, or asthmatic symptoms, with a much smaller percentage being symptom that come from the individual actually having the disease (Castner, Guo, & Yin, 2017).

The methodology used in this study led our group to believe that the results are to be trusted. This study was one of the longests studies our grouped viewed at six years. This is more than a sufficient amount of time to be able to study the trend of asthma over an extended period of time, whereas in a shorter study increases the probability that a certain unusual event could skew the data. The sample size of this experiment was also very large which contributes to the validity of the results.

The final study in New York correlates with the rest of the studies which explored the topic of diesel exhaust particles and NO2 and their association with respiratory symptoms and asthma exacerbations in children (Patel et al. 2013). Their test subjects were children that were both asthmatic and non-asthmatic between theages 14-19. This age group was selected because  their lung development and immune system development were not yet complete, but are nearing the end unlike studying a group of young children. This age group allowed for the scientists to see the short term effects of these air pollutants on the teenagers as well as formulate connections between their current asthmatic symptoms and their history of air pollutant exposure. The subjects of this study were from 2 high schools in New York where there was a black carbon and NO2 concentration that ranked highest in the state. The examination convention was affirmed by the Columbia University Medical Center Institutional Review Board, which is in charge of guaranteeing the moral direct of human research. The New York City Board of Education allowed consent with the prerequisite that school personalities stay secret. The schools were 15 kilometers apart making it easier for the scientists conducting the studies to be able to readily compare results from both schools because they would have been in very similar environmental conditions, and most likely contain a similar concentration of pollutants.

The results of this study indicates that exposure to the traffic related pollutants NO2 as well as the other pollutant studied, black carbon in the short term was associated with an  increase in airway inflammation and oxidative stress that can develop into asthma in the long run. Throughout the study subjects provided 217 exhaled breath condensate samples that were evaluated for pH. Lower exhaled breath condensate pH was associated higher odds of wheezing, shortness of breath, and asthma. In models using data from both schools an increase in the two air pollutants were associated with a decrease in breath condensate pH, hence making them more susceptible to asthma, and the asthmatic symptoms mentioned in the prior sentence. Even among teenagers whose lungs and immune system are more developed than children face the consequences from the current level of pollutants in the air of New York City. It is important for there to be a reduction of these emission in order to ensure that the incidence of asthma and asthma related symptoms does not continue to grow in New York City and in other major cities around the globe.

Conclusion

As we have seen in the studies in all four areas of the world, air pollutants and specifically nitrogen oxides can have detrimental effects on human health. Although nitrogen oxides are not visible to the plain eye, it affects our bodies from the time we are in utero and all throughout adulthood. This air pollutant has been linked to asthmatic symptoms and the onset of asthma, and as cities across the globe industrialize, and the number of cars on the road increases, nitrogen dioxide is becoming more of a threat to our respiratory systems with each passing day. At this point in society it is unrealistic to imagine that humans will prioritize the health and wellbeing of society, as well as the planet, over business so industrialization will only increase. Even though there will inevitably be more cars on the roads that doesn’t mean there is nothing we can do to reduce nitrogen emissions. We can reduce emissions by switching to clean energies instead of burning coal or oil, and start to rely less on standard cars by switching to hybrids or using public transportation (Bel & Holst, 2018). This is only achievable if we continue to conduct research in places like China, Los Angeles, Mexico, and New York City so we can establish a correlation between air pollutants and asthma.

After compiling all of our research together we were able to see common trends in the results, and manners in which these studies were conducted even though they were conducted on different corners of the planet. One major similarity we saw throughout the studies was the use of surveys or questionnaires in order the collect data. Surveys and questionnaires allow researchers to collect data regarding lung function and asthmatic symptoms from the largest group amount of people without asking them to do too much. This allowed for many of our studies to have thousands of participants, which only made the scientists findings more reliable. Another similarity in methodology we saw was the use of ambient air pollution monitoring stations. These stations allowed for the collection of daily data on the concentrations of pollutants in the air, and proved helpful in our investigation as we were able to see the concentration of the focus of our literature review, NO2. A trend in the results we found was that although some studies were able to find a clear correlation between nitrogen oxide pollutant exposure and the incidence of asthma while others only found a connection between the pollution and asthmatic symptoms, all of the studies showed that children are the age group most affected by the air pollutants. The immune systems and respiratory systems of children are not yet fully developed, making them most vulnerable to the harmful effects of nitrogen oxides as well as other air pollutants. This consistent finding throughout all of the studies stresses the importance of a reduction of air pollutant exposure, especially in children, because it will lead to respiratory issues later in life.

Throughout the studies in major cities in China we observed the relationship between NO2 concentration and asthma and other respiratory symptoms. While in utero, fetuses are very vulnerable to the effects of NO2exposure by their mothers, and the study showed that there was a correlation between a mother’s exposure and the chances of the children having an allergic disease such as asthma. In the other three studies children preschool aged through teenagers were observed. All three studies showed that exposure to air pollutants such as NO2had negative effects on their respiratory system as seen through increased asthmatic symptoms like coughing and wheezing, and also a reduced lung function. Although they did not find enough evidence to establish a direct link between NO2and asthma, the studies emphasized that overall air pollutants have a very negative effect on our respiratory systems especially in children while their lungs and immune systems are still developing. The studies made clear that a reduction in air pollutants is needed to ensure that babies and young children’s lungs can develop normally so they function correctly and not lead to complications such as asthma later in life.

The overall consensus in the studies around Mexico’s region is that implementing public transportation in cities does act as an effective deterrent of increasing pollution. All studies focused on transportation in Mexican cities shown at least a 10% reduction in NOx. Although the authors of all the studies agree that air pollution is disastrous for humans. Perez-Cirera et al. (2018) concluded that the people of Mexico city are not aware of social costs of air pollutants. An unfortunate truth that can only be combated by continuing to bring awareness to the public to bring revolutionary design policies to limited air pollution. The studies in Mexico conveyed authenticity by either using previous studies to support their claim, explaining their weaknesses, or had high numbers of subjects.

The studies researched for the city of Los Angeles which, according to Rivero, D. from the project earth website, is the most polluted in the nation because of the surrounding mountains that keep the emissions inside, were all valid because of their similar methodology and time frame. These studies mainly focused on traffic pollution such as, Traffic related air pollution (TRAP) and near roadway air pollution (NRAP), and how they affected respiratory function in children. What unifies these studies is that they all used similar methodology in terms of the children chosen,  measurements of FeNO, and location in Los Angeles. Their subjects were all children, aged from kindergarten through high school, who attended or participated in studies of hospitals in communities of Southern Los Angeles and they were mainly all Hispanic with a few variations in some of the studies. The way they measured for the concentration of the nitric oxides (FeNO) was very similar in all of them and therefore, allows them to be credible. The results they all had concluded that traffic pollution negatively affects the lung respiration of children. These studies were all aware that this was a public health problem and that, in simple terms, the more traffic there is in communities, the more effects it will have on lung function, especially of children.

The studies that were focused in New York showed a generally strong correlation of NO2 leading to or developing asthma or respiratory related problems based on air pollutants that stem from human creation such as vehicles. The first study showed the importance of monitoring air pollution concentrations indoors. Even though a majority of the NO2 emissions that cause asthmatic symptoms in New York City come from traffic this study revealed that the use of stoves and cooking in general contribute greatly to our daily exposure to the gas. Unfortunately, as seen in one instance of the study, sometimes the household emissions produce more NO2 than is filtered out, making it nearly impossible to control the amount we are breathing in. The second study aimed to correlate the presence of pollutants in the air to emergency department visits. This vast study concluded that most of the emergency department visits were diagnosed as ill-defined conditions rather than asthma, but it is important to note that the air pollutant that had the strongest correlation to hospital visits was NO2. Although NO2 was not proven to increase the number of hospital visits for asthma itself, it is clear that the increased pollution did not help to reduce episodes of wheezing, shortness of breath, and coughing in New York citizens. The final study showed that increased exposure to traffic-related pollutants caused an increase in airway inflammation and oxidative stress that could lead to asthma. These results also showed that over time these results are not getting any better. Overall the studies indicated  that air pollution is an uprising problem that can become worse over time and can be detrimental to all humans and all living species. These studies contributed to the idea that NO2 and other air pollutant cause most harm in children rather than adults due to a weak immune system. As citizens of New York these results as well as the findings from the other studies around the world stress the need for change. If society continues this trend we are only doing harm to ourselves, our children, and our planet.

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