Between 2001 and 2008 in the Bronx, New York, there were significant decreases in humidity, sulfur dioxide (SO2), carbon monoxide (CO), and asthma-related emergency department visits throughout all seasons, according to a study published in the Journal of Asthma. There were also increased levels of ozone (O3), spring tree pollen, and temperature throughout the period.

This retrospective study included 42,065 daily values of asthma-related emergency department visits between 2001 and 2008, as well as daily values of SO2, CO, O3, nitrogen dioxide (NO2), humidity, and temperature. Participants included both children and adults. The latter data were collected using the Bronx station of the National Climatic Data Center. Tree pollen counts were collected using the Armonk counting station. The Mann-Whitney test was used to compare values between 2001 and 2004, and 2005 and 2008. Associations between individual pollutants and asthma-related emergency department visits were examined using simple linear regression. Seasons were recorded separately.

Asthma-related emergency department visits decreased during all of the seasons between the 2 time periods (2001-2004 and 2005-2008), as did humidity, SO2, and CO. In the spring and winter, NO2 decreased. O3 increased during the fall, winter, and spring; temperature increased in the winter and summer; and tree pollen increased in the spring. Asthma-related emergency department visits were significantly associated with SO2, CO, NO2, and humidity, and decreased with increasing temperature and O3. The strongest associations were between asthma-related emergency department visits and SO2 (spring) and CO (winter).

Limitations to this study included missing/incomplete data for certain variables (eg, particulate matter data), a small number of hospitals and stations, a lack of accounting for other asthma triggers, a lack of data on the individual level, and the retrospective design.

The researchers wrote that the association between decreased asthma-related emergency visits and increased O3 values  “shows that although O3 is a pollutant that should not be inhaled, it does not have a positive association with [asthma-related emergency department visits].”

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“By tracking and predicting future environmental and air pollutant changes, efforts can be made to notify the public, adjust clinical practice accordingly, and reduce asthma-related [emergency department] visits,” they concluded.


Kordit DS, Reznik M, Leu C-S, Jariwala SP. Longitudinal trends in asthma emergency department visits, pollutant and pollen levels, and weather variables in the Bronx from 2001-2008 [published online March 8, 2019]. J Asthma. doi:10.1080/02770903.2019.1585871