Dust-driven changes in particle pH differentially regulate secondary inorganic aerosol formation in central China

Abstract. Dust episodes facilitate the long-range transport of crustal materials (CM), thereby increasing their contribution to particulate matter and influencing secondary inorganic aerosol (SNA) formation through changes in particle acidity. However, variations in precursor emissions, meteorological conditions, and particle acidity along dust transport pathways may cause the effects of dust input on SNA formation to differ among cities. Such intercity variability during the same regional dust episode remains insufficiently investigated. To address this gap, synchronous observations were conducted in seven cities in central China during a regional dust episode in April 2023. The results showed that, across the seven cities, the mean contribution of CM to PM_2.5 increased from 22.6 % on clean days to 53.2 % on dust days. Correspondingly, particle pH generally increased to 4.24–4.94 during the dust episode, mainly driven by non-volatile cations such as Ca²⁺ and Mg²⁺. Calculations of aqueous-phase sulfate formation rates indicated that transition metal ion (TMI) catalyzed oxidation consistently dominated sulfate formation. However, this pathway was generally suppressed during the dust episode as particle pH increased. Although the O₃ and NO₂ oxidation pathways were enhanced, their increases could not offset the decrease in the TMI-catalyzed pathway. In contrast, elevated particle pH promoted nitrate partitioning. In cities with relatively low clean-day pH values within the rapid-response range of ɛ(NO₃^- ), even a non-maximum dust-induced pH increase could result in a pronounced increase in particulate nitrate. Therefore, future nitrate pollution control should consider the coordinated management of NO_x emissions and fugitive dust sources.