Fine particle pH and its influencing factors during summer at Mt. Tai: Comparison between mountain and urban sites.

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), TNH 3 (= NH 4 + + NH 3) and SO 4 2− 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 TNH 3 could not sufficiently raise fine particle pH to neutral at relatively high SO 4 2− levels, whereas had a significant effect on fine particle pH when SO 4 2− concentration was relatively low. Considering the current levels of TNH 3 in summer of the North China Plain (NCP), fine particle pH was more sensitive to SO 4 2− at present. However, the sensitive factor of fine particle pH in the future is expected to shift from SO 4 2− to TNH 3 with declining SO 2 emissions and increasing NH 3 emissions, leading in turn to the evident increase of fine particle pH. Elevated fine particle pH and abundant TNH 3 may enhance secondary inorganic aerosol production, and thus effectively synergetic control of SO 2 and NH 3 is urgently needed to be considered in the NCP and even in other regions of China. [Display omitted] • The driving factors of fine particle pH at Mt. Tai were analyzed for the first time. • The relative increment [H+] method was firstly adopted to explore pH-WSIs sensitivity. • Fine particle pH in summer of the NCP was sensitive to RH, Temp, TNH 3 and SO 4 2-. • The pH sensitive factor in the future is expected to shift from SO 4 2- to TNH 3. • Synergistic control of SO 2 and NH 3 should be considered to balance fine particle pH. [ABSTRACT FROM AUTHOR]