HONO来源对京津冀大气中二次有机气溶胶浓度影响的模拟研究

Nitrous acid (HONO) plays an important role in enhancing the concentrations of O3 and PM2.5 in the polluted atmospheric boundary layer due to its photolysis into the hydroxyl radical (OH), which is a primary daytime oxidant in the atmosphere. Nevertheless, formation mechanisms of HONO and strength of its sources are not well understood. Unknown HONO sources and their potential impacts on the air quality have gained extensive interests in recent years. In addition, HONO can contribute to the enhancement of the atmospheric oxidizing capacity, potentially leading to the increases in the concentrations of secondary organic aerosols (SOA). SOA is a major component of PM2.5, while its formation processes remain highly uncertain. Current air quality models usually significantly underestimate SOA observations. Therefore, SOA sources and simulations are important weaknesses in the present understanding of atmospheric aerosols. Based on our previous studies, this research will focus on the impacts of four important HONO sources on SOA concentrations. The four HONO sources, i.e., HONO emissions, the reaction of photo-excited NO2 with water vapor, the NO2 hydrolysis on aerosol surfaces, and the photolysis of dry deposited nitric acid (HNO3), will be parameterized and inserted into the fully coupled Weather Research and Forecasting /Chemistry (WRF-Chem) model. The impact of the dry deposited HNO3 photolysis on HONO concentrations will be examined to improve daytime HONO simulations. Then the simulated SOA concentrations in the Beijing-Tianjin-Hebei (BTH) region during February and August of 2007 will be compared to the observed data to validate the SOA simulations. Finally, the impacts of the four HONO sources on SOA concentrations will be quantitatively evaluated and the reasons for SOA enhancements will be illuminated to underscore the potential ways controlling the PM2.5 concentrations in the BTH region.

HONO是OH自由基的重要来源，在污染严重地区，HONO可显著增加O3及PM2.5等的浓度，进而影响空气质量。但HONO来源仍存在争议，HONO来源已成为大气化学领域关注的难点。HONO可增强大气光化学活性，从而可能显著影响二次有机气溶胶（SOA）浓度。作为PM2.5主要组分，SOA的来源仍不确定，目前空气质量模式总明显低估其观测值，所以SOA的来源和模拟是气溶胶研究领域的薄弱点。本项目首先将地表面吸附的HNO3光解反应参数化，并量化该机制对HONO白天浓度的贡献；其次检验耦合HONO四个来源(HONO源排放、NO2*机制、NO2在气溶胶表面的水解反应以及地表面吸附的HNO3光解反应) 后，WRF-Chem模式模拟京津冀地区冬夏季SOA浓度的能力，量化HONO各重要来源对SOA的贡献，改进SOA的模拟；最后阐明HONO各来源影响SOA浓度的主要原因，为PM2.5污染的减控提供科学依据。

HONO是OH自由基的重要来源，在污染严重地区，HONO可显著增加O3及PM2.5等的浓度，进而影响空气质量。但HONO来源仍存在争议，是大气化学领域关注的难点。HONO可增强大气光化学活性，从而可能显著影响二次有机气溶胶（SOA）浓度。作为PM2.5主要组分，SOA的生成机制仍不确定，目前空气质量模式仍明显低估其浓度观测值，也难以准确反映其复杂的物理/化学属性，所以SOA的模拟是气溶胶研究领域的薄弱点。本项目将HONO若干重要来源(HONO源排放、NO2*机制、NO2在气溶胶以及地表面的非均相反应等) 参数化并耦合到入当今世界上最先进的区域空气质量模式之一WRF-Chem模式，定量确定了HONO重要来源对重霾频发的京津冀地区SOA浓度的贡献，并首次发展了可运用于空气质量模式中的预报SOA挥发性和相态等物理/化学属性的新方法，可进一步提高区域空气质量模式模拟并预报该地区重霾污染过程的能力。