11:15 AM - 11:30 AM
[AAS09-09] Modeling ammonia uptake by secondary organic aerosols over Beijing-Tianjin-Hebei area, China
Keywords:WRF-Chem model, Secondary organic aerosol(SOA), Ammonia, Heterogeneous uptake, Nitrogen-containing organic compounds
As the most important alkaline gas in the atmosphere, ammonia (NH3) can react with acidic species to form ammonium salts, which have significant impacts on air quality and human health. Laboratory studies have confirmed that NH3 can react with carbonyl groups in secondary organic aerosol (SOA) to form nitrogen-containing organic compounds (NOCs). This heterogeneous uptake reaction consumes gaseous ammonia thus may have influence on ammonia, inorganic aerosols, or other particulate matters. In order to study the possible impact of this reaction, the first-order loss rate of NH3-SOA uptake reaction was added into the WRF-Chem air quality model for a designed simulation in the North China Plain (NCP) during November of 2017. Modeled average NOCs concentration is 1.60μg m-3 when γ equals 10-5 in the whole NCP area, close to the observed average concentration of 1.52μg m-3. Considering the many other sources of NOCs, we consider γ equals 10-5 to be the upper limit uptake coefficient of the reaction and use it to represent the NH3-SOA uptake reaction in WRF-Chem model. Results of sensitivity studies show slightly changes in NH3 concentration with an average decrease of 0.69 % (0.04μg m-3). In the simulated period, the average percentage change is -0.08% for NO3- , -0.06% for NH4+ and -0.01% for SO42-, which is almost negligible. SOA and PM2.5 aerosols also exhibit non-significant changing patterns where the total effects are -0.03% and 0.03% respectively. Our results reveal that the effect of NH3-SOA heterogeneous uptake is not as significant as the previous research have concluded, and it does not constitute an important factor in model simulation.