Ambient
air pollution and respiratory outcomes including risk of asthma, asthma related
hospitalizations, poor asthma control, overall lung function impairment and
reduced response have been linked. (Neophytou, A. M.,
White, M. J., Oh, S. S., Thakur, N., Galanter, J. M., Nishimura, K. K., . . .
Burchard, E. G., 2016.) Evidence
shows that air pollution exists more in the cities than elsewhere due to
factors such as traffic. According to one study, ambient nitrogen dioxide is a
widely available measure of traffic-related air pollution and is inconsistently
associated with the prevalence of asthma symptoms in children. (Favarato, G., Anderson, H., Atkinson, R., Fuller, G., Mills,
I., & Walton, H., 2014.)

Also according to the same study, a number of
studies have observed associations between the incidence and/or prevalence of
asthma and variations in long-term exposure to nitrogen dioxide within urban
environments in which traffic emissions are the main source of pollution. (Favarato,
G., Anderson, H., Atkinson, R., Fuller, G., Mills, I., & Walton, H., 2014.)
Evidence
for pollution in the cities can also be found based on these four variables
typically found in cities which have been used to study asthma and air
pollution: traffic exhaust, long range transport, soil and road dust, and
coal/oil combustion. (Halonen, J., Lanki,T., Yli-Tuomi, T., Kulmala, M.,
Tiittanen, P., Pekkanen, J., 2007.)

Through systematic review and meta-analysis,
one study strengthened the evidence for an association between NO2 and asthma
among within-community studies in which the exposure contrast is due to traffic
proximity. Their findings showed that NO2 or correlated pollutants may make a
small proportional contribution to asthma prevalence in children. (Favarato,
G., Anderson, H., Atkinson, R., Fuller, G., Mills, I., & Walton, H., 2014.)

Studies have also analyzed asthma in terms of
asthma control, a major goal in asthma management. Of the 481 subjects included
in the analysis, 44% had controlled asthma, 29% had partly asthma, and 26% had
uncontrolled asthma. Those with lower education levels and high smoking levels
had the least controlled asthma. The results also suggested that long-term
exposure to PM10 and 03 is associated with uncontrolled asthma in adults,
defined by symptoms, exacerbation and lung function. Asthma was more often
uncontrolled in women with a p value of 0.04, and in older subjects with a p
value of 0.003. (Bénédicte Jacquemin, Francine Kauffmann, Isabelle Pin, Nicole
Le Moual, Jean Bousquet, Frédéric Gormand, . . . Valérie Siroux, 2012.)

Factors such as age have also been analyzed
in a study whose purpose was to determine the effects of daily variation in levels
of different particle size fractions and gaseous pollutants on asthma and COPD
by age group. By obtaining data on hospital emergency room visits for 1998–2004
for all three public hospitals in the Helsinki metropolitan area, the study was
able to find that the mechanisms of the respiratory effects of air pollution,
and responsible pollutants, differ by age group. (Halonen, J., Lanki,T.,
Yli-Tuomi, T., Kulmala, M., Tiittanen, P., Pekkanen, J., 2007.)

In
analyzing socioeconomic status as it relates to asthma, one study observed stronger
air pollution–pediatric asthma associations in ‘deprivation areas’ (eg, ?20% of
the ZCTA population living in poverty) compared with ‘non-deprivation areas.’ (O’Lenick, C. R., Winquist, A., Mulholland, J. A.,
Friberg, M. D., Chang, H. H., Kramer, M. R., . . . Sarnat, S. E., 2017.) The
study showed that children living in low socioeconomic environments appear to
be especially vulnerable given positive ORs and high underlying asthma ED
rates.

According
to this study, pathways through which low socioeconomic status may lead to
increased susceptibility to air pollution-related childhood asthma include
higher exposures to outdoor and indoor air pollutants, greater psychosocial
stress associated with the social environment. This includes neighborhood
poverty, neighborhood crime levels, parental unemployment, and reduced access
to local resources such as healthy food options, green space, and healthcare
access. (O’Lenick, C. R., Winquist, A., Mulholland, J. A., Friberg, M. D.,
Chang, H. H., Kramer, M. R., . . . Sarnat, S. E., 2017.)

Another
analysis of the occurrence of asthma in the inner cities dealt with those more
likely to live in the city. One study that set out to assess the relationship
between air pollution and lung functionality in minority children with asthma
and possible modification by global genetic ancestry found that particulate
exposures are associated with reduced lung function in these minority
populations. Global genetic ancestry did not appear to significantly modify
these associations, but percent African ancestry was a significant predictor of
lung function. (Neophytou, A. M., White, M. J., Oh, S. S., Thakur, N.,
Galanter, J. M., Nishimura, K. K., . . . Burchard, E. G., 2016.)

According
to the study, this study is the first to report an association between exposure
to particulates and reduced lung function in minority children in which racial/ethnic
status was measured by ancestry-informative markers.

The data presented shows that the main disparities
that exist in terms of vulnerability to asthma and/or an asthma attack include
location as well as wealth, education, and age. Some
of the studies sought to create laws targeting air pollution, such as traffic
laws, whereas other studies analyzed the biological aspects of asthma, such as
ancestry. A common similarity in the research was that the location of all of
the subjects were selected from a major city.