Air pollution and meteorological conditions significantly contribute to the worsening of allergic conjunctivitis: a regional 20-city, 5-year study in Northeast China

This study is the first to explore the potential associations among allergic conjunctivitis (AC), air pollution, and meteorological conditions in Northeast China. Data of meteorology, ambient atmospheric pollutants, and the incidence of allergic conjunctivitis (IAC) in prefecture-level cities between the years 2014 and 2018 are analyzed. The results show an increasing trend in the AC of average growth rate per annum 7.6%, with the highest incidence in the provincial capitals. The IAC is positively correlated with atmospheric pollutants (i.e., PM2.5, PM10, CO, SO2, NO2, and O3) and meteorological factors (i.e., air temperature and wind speed), but negatively correlated with relative humidity. These results suggest that the IAC is directly proportional to pollution level and climatic conditions, and also the precedence of air pollution. We have further obtained the threshold values of atmospheric pollutants concentration and meteorological factors, a turning point above which more AC may be induced. Compared with the air quality standard advised by China and the World Health Organization (WHO), both thresholds of PM10 (70 µg m−3) and PM2.5 (45 µg m−3) are higher than current standards and pose a less environmental risk for the IAC. SO2 threshold (23 µg m−3) is comparable to the WHO standard and significantly lower than that of China's, indicating greater environmental risks in China. Both thresholds of NO2 (27 µg m−3) and O3 (88 µg m−3) are below current standards, indicating that they are major environmental risk factors for the IAC. Our findings highlight the importance of atmospheric environmental protection and reference for health-based amendment.