LAUSR

Abstract Fine particle pH plays an important role in aerosol chemistry. Understanding of influencing factors and evolution process of fine particle pH is helpful to facilitate the improvement of air quality management strategies. Here, we performed simultaneously field measurement at Mt. Tai and the surrounding urban site during the summer of 2018, and analyzed comprehensively fine particle pH and its driving factors based on the sensitivity tests. The results indicated that ambient temperature (Temp), atmospheric relative humidity (RH), TNH3 (= NH4+ + NH3) and SO42− were the dominant factors for fine particle pH. The switch between RH-sensitive and Temp-sensitive regimes with variation of RH at the mountain site implied that fine particle pH was more sensitive to RH at Mt. Tai. Elevated TNH3 could not sufficiently raise fine particle pH to neutral at relatively high SO42− levels, whereas had a significant effect on fine particle pH when SO42− concentration was relatively low. Considering the current levels of TNH3 in summer of the North China Plain (NCP), fine particle pH was more sensitive to SO42− at present. However, the sensitive factor of fine particle pH in the future is expected to shift from SO42− to TNH3 with declining SO2 emissions and increasing NH3 emissions, leading in turn to the evident increase of fine particle pH. Elevated fine particle pH and abundant TNH3 may enhance secondary inorganic aerosol production, and thus effectively synergetic control of SO2 and NH3 is urgently needed to be considered in the NCP and even in other regions of China.