Winter and summer elevations of ozone (O3), sulfur dioxide (SO2), and nitrogen dioxide (NO2) may be associated with moderate to severe asthma exacerbations in nonsmoking adults, according to a study published in Journal of Asthma.

This retrospective study included 143 adults with asthma, in whom 618 exacerbations were recorded between 2005 and 2015. This study took place in a tertiary hospital in Korea. Global positioning system data on air pollution from the national ambient monitoring station were matched to participants using the closest location to each participant’s home address. Conditional logistic regression was used with a time-controlled, bidirectional, symmetrical case-crossover design to assess the relative effects of carbon monoxide, SO2, NO2, O3, and particulate matter <10 μm in diameter (PM10) on asthma exacerbations. Assessments were made from 3 days prior to the exacerbation (T-3) to the day of the exacerbation (T0). Conditional logistic regression was performed for all exacerbations first, then exacerbations were stratified by moderate or acute severity and conditional logistic regression was performed for each group.

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Higher O3 levels were associated with increased asthma exacerbations in summer (odds ratio [OR], 1.012; 95% CI, 1.003-1.02) and winter (OR, 1.009; 95% CI, 1.003-1.016), as were SO2 in the spring (OR, 1.009; 95% CI, 1.000-1.018) and summer (OR, 1.02; 95% CI, 1.006-1.035) and winter NO2 (OR, 1.007; 95% CI, 1.003-1.011). In the summer, 63.2% of exacerbations occurred when T-1 O3 concentrations were significantly elevated compared with control days, while 51% (n=54) of exacerbations occurred in the winter.

In the summer, O3 levels were higher than in the winter on T-1 (245.8 vs 111.7, respectively; P <.0001) and control days (204.0 vs 112.5, respectively; P <.0001). Winter O3 levels were similarly associated with severe vs moderate exacerbations (OR, 1.012; 95% CI, 1.003-1.02 vs OR, 1.01; 95% CI, 0.999-1.021, respectively; P >.05), as were summer O3 levels (OR, 1.006; 95% CI, 1.002-1.009 vs OR, 1.009; 95% CI, 1.003-1.016, respectively; P >.05).

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Limitations to this study included measuring only outdoor air pollutants, not measuring pollen exposure, the retrospective design, small sample size, and not recording observations related to PM2.5.

The study researchers concluded that “[w]e examined the effect of air pollution on the occurrence and severity of asthma exacerbations among currently nonsmoking adult asthmatics and confirmed significant associations of O3, SO2 and NO2 levels with asthma exacerbation. However, the severities of the exacerbation may not be related [to] the levels of these pollutants.”


Shin S-W, Bae D-J, Park C-S, et al. Effects of air pollution on moderate and severe asthma exacerbations [published online May 24, 2019]. J Asthma. doi:10.1080/02770903.2019.1611844