Our goal was to quantify the short-term effects of particulate matter with aerodynamic diameter ≤ 10 μm (PM 10) and nitrogen dioxide (NO 2) on respiratory health of asthmatic children from published panel studies, and to investigate the influence of study and population characteristics as effect modifiers.
After a systematic literature review, we extracted quantitative estimates of the association of PM 10 and/or NO 2 with respiratory symptoms and peak expiratory flow (PEF). Combined effect estimates for an increase of 10 μg/m 3 were calculated by random effects meta-analysis for all studies and for different strata defined by study characteristics. The effect of publication bias was investigated with Egger’s and Begg’s tests and “trim-and-fill” analyses.
We identified 36 studies; 14 were part of the European Pollution Effects on Asthmatic Children in Europe (PEACE) study. Adverse associations of PM 10 with asthma symptoms were statistically significant [odds ratio (OR) = 1.028; 95% confidence interval (CI), 1.006–1.051]. There were also associations, although not statistically significant, of PM 10 with cough (OR = 1.012; 95% CI, 0.997–1.026) and on PEF (decrease of −0.082 L/min; 95% CI, −0.214 to 0.050). NO 2 had statistically significant associations with asthma symptoms in the overall analysis considering all possible lags (OR = 1.031; 95% CI, 1.001–1.062), but not when we evaluated only the 0–1 lag. We found no publication bias, although it appeared when excluding the PEACE studies. When we applied the trim-and-fill method to the data set without the PEACE studies, the results were similar to the overall estimates from all studies. There was an indication for stronger PM 10 associations for studies conducted in summer, outside of Europe, with longer lags, and in locations with higher NO 2 concentrations.
We found clear evidence of effects of PM 10 on the occurrence of asthma symptom episodes, and to a lesser extent on cough and PEF. The results for NO 2 are more difficult to interpret because they depend on the lag times examined. There was an indication of effect modification by several study conditions.