Differences in the morbidity of asthma in multi temperature zones under short-term exposure to air pollution: a systematic review.

Different geographical locations and climatic environments lead to different impacts of specific air pollutants on the relative risk (RR) of asthma morbidity (i.e., new-onset asthma, outpatient visits, emergency department visits, and hospital admissions) in the Northern Hemisphere. Therefore, it is necessary to integrate existing data to assess the impact of short-term exposure to pollutants on the RR of asthma morbidity in the Northern Hemisphere. We conducted a systematic review and meta-analysis to evaluate the effects of short-term exposure to particulate matter (PM_2.5, PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃) on the RR of asthma morbidity. A comprehensive literature search was performed across three major databases: Web of Science, China National Knowledge Infrastructure (CNKI), and PubMed. Ultimately, 14 studies were included in the final analysis. Heterogeneity was evaluated using the Cochran Q test and I² statistics, and publication bias was assessed using Egger's test. The meta-analysis revealed that short-term exposure to five types of air pollutants had a significant impact on the RR of asthma morbidity. Among them, NO₂ exhibited the most significant adverse health effects (RR = 1.02, 95% CI: 1.01-1.03). Stratified analysis showed that residents in the temperate regions were more affected by exposure to SO₂, NO₂, and O₃, whereas residents in the tropical regions were more affected by PM₁₀, and the regional differences in the impact of PM_2.5 on the health of residents in the two regions were not significant. The Egger's test results suggested the presence of a potential publication bias for PM_2.5 and SO₂. In contrast, for PM₁₀, NO₂, and O₃, no publication bias was detected. Therefore, an efficient and resilient public health system should be established.