Abstract. Particle acidity is a fundamental property that affects atmospheric particulate chemistry. Synchronous online monitoring was performed in two urban sites (e.g., Zhengzhou (U-ZZ) and Anyang (U-AY)) and three rural sites (e.g., Anyang (R-AY), Xinxiang (R-XX), and Puyang (R-PY)) in Henan Province during a haze episode to investigate the pH value and its driving factors in the agricultural regions of China. The pH values of particles calculated by ISORROPIA-II model at rural sites were slightly higher than those urban sites, with the median values in the order of 5.2 (4.8–6.9, R-PY) > 5.1 (4.7–6.5, R-AY) > 4.9 (4.1–6.8, R-XX) > 4.8 (3.9–5.9, U-AY) > 4.5 (3.8–5.2, U-ZZ). Sensitivity tests showed that excess ammonia mainly affected the pH value of PM2.5. Moreover, low ammonia determined the high sensitivities of particle pH to sulfate and nitrate at urban sites. Elevated sulfate and nitrate in aerosol caused high pH sensitivity to ammonia. Regional transport may enhance the particle pH value in urban aerosols given the high pH of particles and high ammonia levels in rural and agricultural regions. These results suggest that ammonia is urgently needed to be involved in the regional strategy for the improvement of air quality in China.
Supplementary material to "Role of ammonia on fine-particle pH in agricultural regions of China: Comparison between urban and rural sites"
