Zhao Xiaoxi, Song Min, Zhao Xiujuan, Xue Chaoyang, Liu Pengfei, Ye Can, He Xiaowei, Mu Yujing, Hu Bo
Key Laboratory of Atmospheric Environment and Extreme Meteorology, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Institute of Urban Meteorology, Chinese Meteorological Administration, Beijing 100089, China.
Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; School of Municipal and Environmental Engineering, Shandong Jianzhu University, Ji'nan 250101, China.
Sci Total Environ. 2024 Nov 10;950:175168. doi: 10.1016/j.scitotenv.2024.175168. Epub 2024 Jul 31.
A large fraction of fine particulate matter (PM) and ozone (O) in the troposphere originates from secondary formation through photochemical processes, which remarkably contributes to the deterioration of regional air quality in China. The photochemical reactions initiated by hydroxyl radicals (OH) play vital roles in secondary PM and O formation. In contrast, the OH levels in polluted areas are underestimated by current chemical transport models (CTMs) because of the strongly unknown daytime sources of tropospheric nitric acid (HONO), which has been recognized as the dominant source of primary OH in polluted areas of China. In this study, the atmospheric HONO levels at two urban sites were found to be significantly underestimated by the WRF-Chem model based on available information on HONO sources. The HONO levels could be well reproduced by the WRF-Chem model after incorporating two new potential HONO sources from the photochemical reactions of NO, as proposed in our previous study based on chamber experiment results. Comparing the simulations with available information of HONO sources, the simulated levels of atmospheric OH, secondary inorganic and organic aerosols (SIA and SOA), PM and daily maximum 8-h average (MDA8) O were evidently elevated or were closer to the observations over the North China Plain (NCP), with elevation percentages of 0.48-20.1 %, and a decrement percentage of -5.79 % for pNO. Additionally, the compensating errors in modeling PM and the gap in MDA8 O levels between observation and simulation in 2 + 26 cities became evidently smaller. The results of this study indicated that the empirical parameterization of two new potential HONO sources through photochemical reactions of NO improved the model performance in modeling PM and O by narrowing the gap in daytime HONO levels between simulation and observation, although their detailed chemical mechanisms are still unknown and should be further investigated and explicitly parameterized.
对流层中很大一部分细颗粒物（PM）和臭氧（O₃）源自光化学过程引发的二次形成，这对中国区域空气质量恶化有显著影响。由羟基自由基（OH）引发的光化学反应在二次PM和O₃形成过程中起着至关重要的作用。相比之下，由于对流层硝酸（HONO）白天来源极不明确，当前的化学传输模型（CTM）低估了污染地区的OH水平，而HONO已被认为是中国污染地区主要OH的来源。在本研究中，基于HONO源的现有信息，发现WRF - Chem模型显著低估了两个城市站点的大气HONO水平。根据我们先前基于腔室实验结果提出的建议，将NO光化学反应产生的两个新的潜在HONO源纳入WRF - Chem模型后，HONO水平能够得到较好的再现。将模拟结果与HONO源的现有信息进行比较，模拟的大气OH、二次无机和有机气溶胶（SIA和SOA）、PM以及日最大8小时平均（MDA8）O₃水平在华北平原（NCP）明显升高或更接近观测值，升高百分比为0.48 - 20.1%，pNO的下降百分比为 - 5.79%。此外，2 + 26城市中PM建模的补偿误差以及观测与模拟之间MDA8 O₃水平的差距明显变小。本研究结果表明，通过NO光化学反应对两个新的潜在HONO源进行经验参数化，通过缩小模拟与观测之间白天HONO水平的差距，改善了模型在PM和O₃建模方面的性能，尽管它们详细的化学机制仍然未知，应进一步研究并明确参数化。
