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Ammonium may emerge as the primary driver of future aerosol acidity, replacing the historical role of sulfate over the coastal area of North China: Insights from a megacity (Qingdao).

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Title: Ammonium may emerge as the primary driver of future aerosol acidity, replacing the historical role of sulfate over the coastal area of North China: Insights from a megacity (Qingdao).
Authors: Li, Wenshuai1,2,3 (AUTHOR), Song, Yaoyu1,2 (AUTHOR), Chen, Tianshu1,2 (AUTHOR), Qi, Yuxuan1,2 (AUTHOR), Wu, Guanru1,2 (AUTHOR), Wang, Xinshuo1,2 (AUTHOR), Xie, Wenwen4 (AUTHOR), Sheng, Lifang1,2 (AUTHOR), Wang, Wencai1,2 (AUTHOR), Qu, Wenjun1,2 (AUTHOR) quwj@ouc.edu.cn, Zhou, Yang1,2 (AUTHOR) yangzhou@ouc.edu.cn
Source: Atmospheric Environment. Jun2026, Vol. 374, pN.PAG-N.PAG. 1p.
Subject Terms: *Ammonium, *Sulfates, *Atmospheric aerosols, *Aerosols, *Air pollution, *Particulate matter, Nitric acid
Geographic Terms: China, Qingdao (China)
Abstract: Aerosol acidity serves as a critical environmental parameter, governing gas-particle partitioning and pH-dependent reactions central to secondary aerosol formation. In recent decades, the chemical composition of aerosols in China has been significantly influenced by modifications in anthropogenic precursor emissions. Therefore, we investigated the changes in aerosol acidity of fine particles (PM 2.5) and corresponding driving factors during a period of over 10 years in Qingdao, a coastal city in North China located in the East Asian continental outflow region. A significant decadal increase in aerosol pH was observed, most pronounced in winter (from 0.93 to 3.76), followed by summer (from 0.85 to 2.10) and autumn (from 1.57 to 3.64). This increase was driven by substantially reduced SO 4 2− and elevated total ammonia (TNH x) across all seasons except spring, during which aerosol pH decreased slightly (from 2.97 to 2.30). In the "pollution season" (i.e., winter), compared with reducing SO 4 2− and total nitric acid (TNO 3), a reduction in TNH x can exert a significantly greater impact on aerosol pH and have a greater potential to reduce water-soluble ions concentrations via modulating phase partitioning. Under the scenarios assuming a comparable or larger reduction in TNO 3 relative to TNH x , aerosol pH is more likely to decrease rather than increase in the long term in winter, with PM 2.5 pH ranging from 1.6 to 4.2. Given the current challenges in reducing TNH x levels, reducing TNO 3 remains an effective strategy for decreasing water-soluble ions content in PM 2.5. [Display omitted] • Decadal increase in PM 2.5 pH was driven by declining SO 4 2− and rising total ammonia (TNH x). • PM 2.5 pH is expected to remain stable in the near term but decline in the long term. • Reducing TNH x has a stronger influence on pH than reducing SO 4 2− or total nitric acid (TNO 3) in winter. • Reducing TNO 3 is an effective strategy in lowering PM 2.5 when ammonia mitigation is challenging. [ABSTRACT FROM AUTHOR]
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Abstract:Aerosol acidity serves as a critical environmental parameter, governing gas-particle partitioning and pH-dependent reactions central to secondary aerosol formation. In recent decades, the chemical composition of aerosols in China has been significantly influenced by modifications in anthropogenic precursor emissions. Therefore, we investigated the changes in aerosol acidity of fine particles (PM 2.5) and corresponding driving factors during a period of over 10 years in Qingdao, a coastal city in North China located in the East Asian continental outflow region. A significant decadal increase in aerosol pH was observed, most pronounced in winter (from 0.93 to 3.76), followed by summer (from 0.85 to 2.10) and autumn (from 1.57 to 3.64). This increase was driven by substantially reduced SO 4 2− and elevated total ammonia (TNH x) across all seasons except spring, during which aerosol pH decreased slightly (from 2.97 to 2.30). In the "pollution season" (i.e., winter), compared with reducing SO 4 2− and total nitric acid (TNO 3), a reduction in TNH x can exert a significantly greater impact on aerosol pH and have a greater potential to reduce water-soluble ions concentrations via modulating phase partitioning. Under the scenarios assuming a comparable or larger reduction in TNO 3 relative to TNH x , aerosol pH is more likely to decrease rather than increase in the long term in winter, with PM 2.5 pH ranging from 1.6 to 4.2. Given the current challenges in reducing TNH x levels, reducing TNO 3 remains an effective strategy for decreasing water-soluble ions content in PM 2.5. [Display omitted] • Decadal increase in PM 2.5 pH was driven by declining SO 4 2− and rising total ammonia (TNH x). • PM 2.5 pH is expected to remain stable in the near term but decline in the long term. • Reducing TNH x has a stronger influence on pH than reducing SO 4 2− or total nitric acid (TNO 3) in winter. • Reducing TNO 3 is an effective strategy in lowering PM 2.5 when ammonia mitigation is challenging. [ABSTRACT FROM AUTHOR]
ISSN:13522310
DOI:10.1016/j.atmosenv.2026.121947