Industrial Emissions and Asthma Prevalence

The pathogenesis of asthma is multifactorial and not completely understood; however, it is considered a chronic inflammatory disease that affects the airways and has a clinical development of wheezing, shortness of breath, chest tightness, and cough. The prevalence of asthma has increased drastically during the past few decades. Urban air pollution from industrial emissions has been implicated as one of the major factors responsible for this increase. The objective of this paper was to analyze the impact of sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2) on the overall prevalence of asthma for adults and children. The statistical analysis was conducted using SAS statistical software to determine multiple comparison tests for asthma prevalence among years, ages, ethnicities, and gender, and emissions of SO2, NOx, and CO2 among regions and years. Moreover, SAS was utilized to estimate fully parametric regression models for emission density on total asthma prevalence, child asthma, and adult asthma. In our investigation of asthma prevalence, blacks, females, and children were found to have the highest incidence of asthma. Industrial emissions of SO2, NOx, and CO2 were analyzed, and CO2 had the largest emissions, followed by SO2, and lastly NOx. NOx had the highest correlation with asthma prevalence in child and adult asthma; however, when the influence of SO2, NOx, and CO2 on the overall asthma rate was investigated, CO2 showed the highest correlation. Furthermore, children exposed to SO2, NOx, and CO2 were found to have an increased risk of asthma when compared to adults. This adds to evidence that outdoor air pollution is associated with asthma and that more needs to be done to decrease industrial air pollution.


INTRODUCTION
Asthma is a substantial cause of morbidity and mortality whose prevalence has nearly increased 2-folds in the past 20 years (Lim et al., 2007;Price et al., 2017). The pathogenesis of asthma is multifactorial and not completely understood; however, it is considered a chronic inflammatory disease that affects the airways and has a clinical development of wheezing, shortness of breath, chest tightness, and cough (Barrios et al., 2006, Edwards et al., 2017. Asthma is a growing concern and a major public health issue affecting 13% of the United States population (Nunes et al., 2017) and accounting for 3,396 deaths annually (Patel et al., 2018). There are approximately 26 million patients with physician-diagnosed asthma in the United States (US) (Yaghoubi et al., 2019). This chronic disease affects all ages and causes over 1 million emergency department visits and over 150,000 hospitalizations with a cost of approximately $80 billion in medical expenses annually (Yaghoubi et al., 2019).
The propensity to acquire asthma can be inherited, but genetic components are unlikely to be the cause of this significant increase that has occurred in the past 20 years (Woodruff et al., 2004;Yang et al., 2017). Scientists have shown that air pollution from vehicles, industries, and power plants is a major source for asthma attacks (Anenberg et al., 2018). Scientific evidence has shown that several environmental pollutants, both indoor and outdoor, exacerbate asthma. These environmental pollutants include exposure to dust mites, tobacco smoke, cockroaches, nitrogen dioxide (NO2), pesticides, plasticizers, and volatile organic compounds (VOCs) (Guarnieri and Balmes, 2014;Woodruff et al., 2004).
Current research is being conducted to fully understand the link between industrial emissions and asthma incidence and prevalence. There have been several studies showing that chronic exposure to ozone is associated with the development and exacerbation of asthma (Avol et al., 2001;Goodman et al., 2018;McConnell et al., 2002;Zu et al., 2017. Moreover, other studies found that exposure to particulate matter affects asthma (Cesar et al., 2016, Ware et al., 1993, Zuo et al., 2019. Lastly, industrial emissions of carbon dioxide (CO2) and sulfur dioxide (SO2) have been associated with asthma prevalence (Reno et al., 2015).
Nitrogen dioxide and nitric oxide are referred to together as nitrogen oxides (NOx). NOx gases react to form smog as well as being paramount to the development of fine particles (PM) and ground level ozone, both of which are linked with adverse health effects. A recent study revealed a statistically significant association between outpatient visits and hospitalizations due to bronchitis and asthma exacerbation and daily nitrogen oxides concentrations (Kowalska et al., 2020). With the continued industrialization worldwide, it is essential to refine our understanding of the mechanisms behind asthma associated with inhaled environmental exposure to air pollutants.
Power plants accounted for approximately 64% of SO2 emissions, 16% of NOx emissions, and 40% of CO2 emissions in the United States (Amster and Lew Levy, 2019;Massetti, 2017;Van Atten, 2012). Both SO2 and NOx are categorized as National Ambient Air Quality Standards (NAAQS) by the EPA due to their adverse effects on human health and the environment. CO2 is a notable greenhouse gas that thrives as a main pollutant that is warming the Earth. CO2 is considered to be a pollutant when associated with cars, planes, power plants, and other anthropogenic activities that involve the burning of fossil fuels such as gasoline and natural gas (Chen et al., 2020). Furthermore, CO2 is deemed as the most prevalent of anthropogenic greenhouse gas emission and the electric industry accounts for more CO2 emissions than any other sector, including industrial and transportation sectors (Quick and Marland, 2019). Since the association of ground level ozone and particulate matter on asthma has been extensively studied, the focus of our study will examine the industrial emissions of the primary pollutants SO2, NOx, and CO2 on the prevalence of asthma. The objective of this paper was to determine the prevalence of asthma across the contiguous United States among regions, age, gender, and ethnicity (African American, Caucasian, or Hispanic) for 2006-2011. We also analyzed the emissions of SO2, NOx, and CO2 by industries per region during 2006-2011. Lastly, we analyzed the impact of SO2, NOx, and CO2 on the overall prevalence of asthma, child asthma, and adult asthma. We hypothesize industrial emissions of SO2, NOx, and CO2 are directly correlated with asthma prevalence for total asthma, child asthma, and adult asthma.

Data Collection
The data used in this study is summarized in Table 1. The Centers for Disease Control and Prevention, National Center for Health Statistics, National Health Interview Survey (NHIS) was used to determine the prevalence of asthma among region, age, race, and gender for 2006-2011. The NHIS is a continuing nationwide sample survey of the civilian non-institutionalized population gathered by personal household interviews. The United States Environmental Protection Agency (USEPA), Air Markets Program Data (AMPD), was employed to collect the industrial emissions of SO2, NOx, and CO2 for each state during 2006-2011. The total land area for each state was retrieved from the United States Census Bureau to determine the density of emissions in tons per acre of land for each state.

Data Analysis
The data was stored and sorted in Microsoft Excel. The concentrations of the pollutants were given for each state; therefore, the data for each state had to be sorted and means calculated for each region ( Table 2). The total land area for each state was retrieved and stored in Microsoft Excel (2010). The density of pollutant per state was found by taking the ratio of the total emissions per pollutant (tons) by the total land area for each state (acres). The density was then averaged per region. Once the data was sorted, the statistical analysis was conducted using SAS statistical software (Weaver and Wuensch, 2013). To find means and p-values, multiple comparison tests like PROC GLM/tukey (General Linear Models) was used to estimate asthma prevalence among years, ages, ethnicities, and gender, and emissions of SO2, NOx, and CO2 among regions and years. Parametric regression model, PROC REG was used to estimate the relationships among emission density, total asthma prevalence, child asthma, and adult asthma.  Table 3 and Figure 1 summarize the asthma prevalence. The p-values for the asthma prevalence among ages, ethnicity, and gender all had a p-value less than .05 while the asthma prevalence among years had a p-value less than 0.10. The statistical analysis revealed that the age groups (5-14) and (15)(16)(17)(18)(19) have asthma prevalence means that were significantly different from all other age groups. Moreover ages 5-14 had a higher prevalence of asthma than any other age group. The other age groups did not have asthma prevalence means that were significantly different from any other age group. Blacks had the highest incidence of asthma when compared to Hispanics and Caucasians. All ethnicities have asthma prevalence means that were significantly different from each other (Table 4). Also, the means of asthma prevalence among gender were significantly different, and females had a greater incidence of asthma than males. The prevalence of asthma has been consistent from 2006-2011; thus, none of the years had significantly different means.

Asthma Prevalence
Our study determined the regional prevalence of total asthma, child asthma, and adult asthma during 2006-2011. The means of total asthma rates were placed in two groups: the Northeast and Midwest in one group while the South and West were in the other. This indicated that the means of total asthma prevalence were significantly different for the Northeast and Midwest when compared to the South and West. The means among child asthma was only significantly different in the West. Also, the West had the lowest incidence  of child asthma when compared to other regions. In adult asthma, the Northeast and South had significantly different means. Figure 2 shows the incidence of child asthma and adult asthma by region. Figure 3 illustrates the distribution of the data for total asthma, child asthma, and adult asthma.

Regional Emissions of SO2, NOx, and CO2 during 2006-2011
The regional emissions of SO2, NOx, and CO2 were determined by grouping the states into regions and finding the mean of each region. CO2 levels were much higher than SO2 and NOx levels; therefore, CO2 was illustrated separately from SO2 and NOx. As shown in Figure 4 (Figure 5). The statistical analysis revealed that the Northeast and West had significantly different means than the Midwest and South for SO2 and NOx while there were no regions with significantly different means for CO2 (Figure 6).

The Impact of SO2, NOx, and CO2 Asthma Prevalence
The impact of SO2, NOx, and CO2 on total asthma prevalence was investigated in this study. The results yielded a weak correlation between SO2, NOx, and CO2 on the total prevalence of asthma (Figure 7); however, CO2 had the strongest correlation (R 2 = .3027) when compared to SO2 and NOx on the total asthma prevalence. We also evaluated the correlation between SO2, NOx, and CO2 on child and adult asthma separately. These results differ greatly from the overall asthma correlations. There was a stronger correlation (R 2 =0.5998) found between NOx and child asthma (Figure 8) when compared to any other correlation in the study. Furthermore, SO2 (R 2 = .4501) contributes to child asthma more than CO2 (R 2 =.3927). Correlations among adult asthma and SO2, NOx, and CO2 were determined (Figure 9). NOx had the highest correlation (R 2 =.2253) among adult asthma followed by SO2 (R 2 =.1813) and finally CO2 (R 2 =.0196).

DISCUSSION
Our study found the prevalence of asthma among years, regions, ages, ethnicities, and gender during 2006-2011. African ancestry has been linked to asthma, and elevated asthma rates in blacks can be partially attributed to African genetic ancestry (Daya and Barnes, 2019;Flores et al., 2012). Moreover, asthma prevalence is disproportionately high among African American women in the United States (Janevic et al., 2012;Tran and Tran, 2020). Epidemiological studies have shown that the prevalence of adult asthma and severe asthma is higher in women (Fuseini and Newcomb, 2017;Takeda et al., 2013). Our study confirms previous research regarding blacks and women having the highest prevalence for asthma in the United States. The causation of this high prevalence among has not been fully found; however, lower socioeconomical status and less education has been associated with being the main culprits for blacks carrying such a high prevalence for asthma.
Asthma is much more common in children than adults. Asthma is the most common chronic childhood disease that affects nearly 7 million children in the United States (Orellano et al., 2017). Non-Hispanic black children have been reported to be more likely to have ever been diagnosed with asthma (22%) or to still have asthma (17%) than Hispanic children 13% (ever diagnosed) and 8% (still diagnosed) or non-Hispanic white children (12% and 8%, respectively) (Walker, 2012). Our study had similar results that children aged 5 to 14 and 15 to 19 had the highest prevalence for asthma when compared to any other age group.
Our study validated that power plant emissions of SO2 were greater than the emissions of NOx (Massetti, 2017). Our collected data also determined that from 2006 through 2011, the levels of emissions for both pollutants have declined. We also found that emissions of CO2 drastically surpassed that of SO2 and NOx during 2006 to 2011. M. J. Bradley & Associates (2012) stated that the total generation among the 100 largest power producers for 2010 had SO2 emissions ranging from 0 to 498,009 tons, NOx emissions ranging from 0 to 129,951 tons, CO2 emissions ranging from 0 to 155 million tons. CO2 emissions from power plants are largely unregulated at the federal level (Van Atten, 2012). Thus, more CO2 is being released. Since 1990, there has been a notable decrease in the power plant emissions of SO2 and NOx (Massetti, 2017). This was seen in our study as well. M. J. Bradley & Associates (2012) reported that there has been a 68% decline of NOx and SO2 emissions from 1991 to 2010 due to the implementation of the 1990 Clean Air Act Amendments (Van Atten, 2012). However, the Clean Air Act amendments did not contain any regulations for CO2; therefore, the emissions of CO2 have increased since 1990. In 2010, power plant emissions of CO2 were 24% higher than 1990, and between 2009 and 2010, power plant emissions of CO2 increased by 5% due to economic growth resulting in higher energy consumption across all sectors (Van Atten, 2012). The electric power industry is constantly transforming as new policies and procedures are in place in order to reduce air pollution emissions. Furthermore, the industrial companies are deciding to discontinue the use in the number of coal-fired generating plants as natural gas prices has declined making the use of fossil-fired power plants more economically feasible (Massetti, 2017).
Our study also investigated the impact of SO2, NOx, and CO2 on overall asthma prevalence, child asthma, and adult asthma. The highest correlation between the three pollutants of interest was found in child asthma compared to overall asthma prevalence and adult asthma. Therefore, children exposed to SO2, NOx, and CO2 have elevated risks of asthma. Children are more susceptible to asthma and other respiratory illnesses (Goldizen et al., 2016;Perera, 2017;Tzivian, 2011). The National Academy of Sciences has found that in general, children are more susceptible to environmental toxins than adults because children consume more food and water relative to their total body surface area compared to adults. Therefore, they are exposed to more environmental toxins relative to their body mass index. Children also have a more rapid respiratory rate and take in a greater volume of air per unit of body mass index than adults (Orellano et al., 2017;Tzivian, 2011). Moreover, children's organs systems are immature making them more vulnerable and less able to detoxify hazardous chemicals. Also, human lungs do not develop completely until the sixth to eighth year of life. During these early years, exposure to even mild chemical irritants can have significant effects on respiratory development (Goldizen et al., 2016;Tzivian, 2011).
The prevalence of asthma has increased drastically during the past few decades. Urban air pollution from industrial emissions has been implicated as one of the major factors responsible for this increase. Our study revealed industrial emissions of CO2 as being associated with total asthma prevalence. Anthropogenic increases in global atmospheric CO2 concentration have been shown to stimulate earlier and greater production of allergenic pollen (Reinmuth-Selzle et al., 2017, Wolf et al., 2010. Studies have shown that a doubling of the atmospheric CO2 concentration stimulated ragweedpollen production by 61% (P = 0.005) (D' Amato et al., 2013, D'Amato et al., 2016. CO2 may also increase airborne fungal spores (Pringle, 2013, Wolf et al., 2010. Pollen and fungal spores are known aggravators of asthma. Thus, increase concentration of CO2 may exacerbate asthma by increasing the production of pollen and fungal spores. Children asthma was found to be affected most by NOx than the other pollutants that were studied. NO2 levels in the ambient air have been shown to be associated with emergency department visits for pediatric asthma (Burbank and Peden, 2018;Strickland et al., 2010). Studies found a statistically significantly increased risk of asthma diagnosis with increased early life exposure to NO and NO2 (Clark et al., 2010;Khreis et al., 2017). This data supports that early childhood exposure to air pollutants plays a role in development of asthma. Lobdell et al (2011) used traditional epidemiological study designs in small communities in New Haven to identify linkages between reduction in NOx and improvements in prevalence of asthma in children and adults (Lobdell et al., 2011). They concluded that a substantial reduction in air pollution (e.g., ~ 60% for NOx) are needed to improve health impacts of pollutants on asthma (Lobdell et al., 2011). NOx is a principal precursor for the formation of ground level O3. NOx has a direct correlation with O3 in the atmosphere and in the ambient air. Several studies report that chronic exposure to ozone is associated with the development of asthma (Avol et al., 2001;Gauderman et al., 2002;Goodman et al., 2018;McConnell et al., 2002;Schultz et al., 2017). Therefore, NOx is not only exacerbating asthma by itself, but it is also affecting asthma by producing O3.

CONCLUSION
In our investigation of asthma prevalence, blacks, females, and children were found to have the highest incidence of asthma. Industrial emissions of SO2, NOx, and CO2 were analyzed, and CO2 had the largest emissions, followed by SO2, and lastly NOx. However, NOx had the highest correlation with asthma prevalence in child and adult asthma. But, when the influence of SO2, NOx, and CO2 on the overall asthma rate was investigated, CO2 showed the highest correlation. Furthermore, children exposed to SO2, NOx, and CO2 were found to have an increased risk of asthma when compared to adults. This adds to evidence that outdoor air pollution is associated with asthma. The risk increase is small; however, the risk independently or jointly with genetic factors may explain why the prevalence of asthma has risen in the past 20 years.