Chemical characterization of submicron aerosol in summertime Beijing: A case study in southern suburbs in 2018
2020
Chen, Tianzeng | Liu, Jun | Liu, Yongchun | Ma, Qingxin | Ge, Yanli | Zhong, Cheng | Jiang, Haotian | Chu, Biwu | Zhang, Peng | Ma, Jinzhu | Liu, Pengfei | Wang, Yafei | Mu, Yujing | He, Hong
Atmospheric particulate matters have a crucial impact on climate change, visibility and human health. In this study, a detailed characteristic of summertime PM₁ was real-time measured in south suburb of Beijing from 16ᵗʰ August to 16ᵗʰ September 2018. Averaged PM₁ concentration of 24.1 ± 18.0 μg m⁻³ was observed, consisting of OM (50.8%), SO₄²⁻ (16.0%), BC (13.2%), NO₃⁻ (10.2%), NH₄⁺ (9.2%), and Cl⁻ (0.6%). There was an accumulation mode with a peak diameter of ∼500 nm for all the species (except BC), and OM was additionally characterized by a smaller mode of <100 nm. Elemental analysis of OM showed that the diurnal variations of H/C, O/C, N/C, and S/C were correlated to the photochemical and aqueous-phase process. Four organic factors including one hydrocarbon-like (HOA) and three oxygenated (LO-OOA, SV-OOA and MO-OOA) organic aerosol factors were identified by positive matrix factorization (PMF) analysis. The contributions of these factors varied with PM₁ concentration and their average values were 31%, 30%, 14%, and 25%, respectively. Contribution of HOA was RH-independent but decreased with the increasing PM₁ concentration, while OOA factors were a combined result of RH and Oₓ (=O₃+NO₂), revealing the important role of photochemical and aqueous-phase process in OA evolution. The contribution of SV-OOA with the highest S/C increased significantly with RH, indicating a certain number of S-containing organics. Our results also showed that secondary OA was the dominant species, as well as increased with the pollution level, implicating VOCs and NOₓ should be controlled to relieve the secondary OA pollution.
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