Physicochemical Characterization of Religious Burning Aerosols in Lhasa on the Qinghai‐Tibet Plateau.

Religious burning (RB) has been identified as a major source of atmospheric aerosols on the Qinghai‐Tibet Plateau. However, there is limited understanding of the detailed chemical composition, size distribution, and optical properties of RB aerosols in this region. To characterize these important aerosol properties, ambient PM2.5 and size resolved aerosols from RB emissions in Lhasa were collected during summer 2019. Organic functional group (OFG) and inorganic ion composition was measured using Fourier transform infrared spectroscopy and ion chromatography, respectively. The ambient PM2.5 was dominated by organic components, with the OFG concentrations significantly higher during religious events, reflecting the substantial impact of RB emissions on local air quality. The RB aerosols were characterized by high fractions of alkane (34%), hydroxyl (29%), and carboxylic acid (13%) groups, with peak mass in the accumulation mode (0.56–1.00 μm). The high abundance of hydroxyl group and the size distribution pattern suggested that the RB aerosols were formed from volatilization of fuel materials followed by unaltered condensation, a process that may be unique to the low‐temperature, low‐oxygen burning in the scattered burners at the temples. The absorption coefficient of RB aerosols showed similar size distribution to the mass size distribution, but the absorption Ångström exponent displayed the lowest value in the 0.56–1.00 μm size mode. This specific size distribution aligned with the mass fraction of carboxylic acids and mirrored the mass proportion of alkanes, suggesting that smaller and larger particles were enriched with substances that have higher light‐absorbing capabilities. Plain Language Summary: Religious burning (RB) has been found to be a major source of air pollution particles on the Qinghai‐Tibet Plateau. However, much remains to be learned about the chemical composition, size distribution, and light‐absorbing properties of these particles. To better understand these properties, we collected particles from ambient air and the RB emissions in Lhasa during the summer of 2019 and measured the organic and inorganic components of the particles. RB particles were made of high amounts of alkane (34%) and hydroxyl (29%) groups, which had a big impact on local air quality. The high amount of hydroxyl group and the size pattern suggest that the RB particles were formed when fuel materials evaporate and then condense, which may be unique to the low‐temperature, low‐oxygen burning in the scattered burners at the temples. The light‐absorbing properties of the RB particles showed a similar size pattern to the mass size distribution, but the smallest and largest particles had higher light‐absorbing abilities. This specific size distribution matches the percentage of carboxylic acids and is the opposite of the amount of alkanes, suggesting that smaller and larger particles were enriched with substances that can absorb more light. Key Points: Lhasa PM2.5 is primarily composed of hydroxyl, alkane, and carboxylic acid groups, heavily influenced by religious burning (RB) activitiesFresh RB aerosols are likely formed via volatilization and condensation processes during the low‐temperature and low‐oxygen burningThe Ångström exponent of water‐soluble organic carbon in RB aerosols shows an opposite size distribution to the mass and absorption coefficient of the aerosols [ABSTRACT FROM AUTHOR]