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There is a need to understand the impacts of ambient aerosol acidity on the photosynthetic process in terrestrial plants and its connection to carbon storage. To help address this need, we conducted a study to investigate the acidity of ambient aerosol on the stability of chlorophyll, the main indicator of photosynthetic processes in leaves. Ambient fine particulate matter (<2.5 μm in aerodynamic diameter or PM2.5) sampled at a suburban site of Nanjing during cold seasons of 2019 and 2020 was collected. Ambient levels of gaseous pollutants including NO2, SO2, and CO; daily maximum 8 h average O3 concentration (O3-8h); and daily meteorological parameters were also recorded. Water-soluble ions of F–, Cl–, NO3 –, SO4 2–, NH4 +, Na+, K+, Mg2+, and Ca2+ in collected PM2.5 samples were determined using an ion chromatograph. The Extended Aerosol Inorganics Model version IV (E-AIM IV) was used to estimate the total acidity and in situ pH of collected PM2.5 samples, while Positive Matrix Factorization 5.0 (PMF) was used to apportion emission sources. Depletion of chlorophyll a and b was determined using water extracts of collected PM2.5 samples. Estimated in situ pH levels of collected PM2.5 samples were in the range of pH 2–4. Associations were found between the concentration of SO4 2– and the total acidity of ambient PM2.5 particles. Source apportionment results showed that five PM sources including dust source (DS), secondary source (SS), industrial source (IS), mobile source (MS), and biomass burning (BB) contributed to aerosol acidity of ambient PM2.5 particles. Aerosol acidity, rather than PM2.5 mass, resulting from water-soluble ions in gaseous pollutants was the dominant factor influencing the stability of chlorophyll a. Alternatively, chlorophyll b was found to be stable with the exposure to water extracts of ambient PM2.5 particles within 60 h. This study provides the first field evidence that aerosol acidity could result in the depletion of chlorophyll a.

Submicron soot particles (<1.0 μm in aerodynamic diameter) are responsible for global warming and health burdens worldwide. However, studies on bio-monitoring of submicron soot particles and their associated sources by...

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