NUMERICAL SIMULATION WITH A COMPREHENSIVE CHEMICAL TRANSPORT MODEL OF NITRATE, SULFATE, AND AMMONIUM AEROSOL DISTRIBUTIONS OVER EAST ASIA

The transport and chemical production processes of nitrate, sulfate, and ammonium aerosols over East Asia were investigated by use of the Models-3 Community Multi-scale Air Quality （CMAQ） modeling system coupled with the Regional Atmospheric Modeling System （RAMS）. For the evaluation of the model＇s ability in depicting their 3-dimensional concentration distributions and temporal variations, modeled concentrations of nitrate, sulfate, and ammonium aerosols are compared with the observations obtained at a ground station in Japan in March 2001 and onboard of an aircraft DC-8 on 18 and 21 March 2001 during the Transport and Chemical Evolution over the Pacific （TRACE-P） field campaign. Comparison shows that simulated values of nitrate, sulfate, and ammonium aerosols are generally in good agreement with their observed data, and the model captures most important observed features, and reproduces temporal and spatial variations of nitrate, sulfate, and ammonium aerosol concentrations reasonably well, e.g., the timing and locations of the concentration spikes of nitrate, sulfate, and ammonium aerosols are well reproduced, but large discrepancies between observed and simulated values are also clearly seen at some points and some times due to the coarse grid resolution and uncertainties of the emissions used in this study. This comparison results indicate that CMAQ is able to simulate the distributions of nitrate, sulfate, and ammonium aerosols and their related species in the troposphere over East Asia reasonably well.     

Models-3/CMAQ和CAMx对珠江三角洲臭氧污染模拟的比较分析

运用Models-3/CMAQ和CAMx两个区域空气质量模式同时对珠江三角洲2004年10月的臭氧污染进行模拟,利用监测网12个站点的观测数据对两个模式的臭氧模拟效果进行统计评估,并应用过程分析技术,量化各种大气物理、化学过程对臭氧浓度变化的影响,探讨两个模式结果偏差产生的主要原因.CMAQ与CAMx均能较好地模拟出珠江三角洲大多数站点的臭氧浓度水平和变化趋势,与监测值的相关系数分别为0.73,0.74,标准化平均偏差分别为-8.5%、8.8%、标准化平均误差分别为36.7%和37.9%;两个模式的模拟结果具有很高的相关性（相关系数R为0.92）和较为一致的空间分布,但CMAQ的臭氧模拟浓度总体上较CAMx的结果偏低约17%.两个模式对珠江三角洲不同地区、不同类型站点的模拟结果一致性不尽相同.在干沉降、化学反应参数、垂直输送等方面处理方法上的差异共同造成了两个模式对珠江口沿岸站点臭氧模拟结果上的差别;细网格边界浓度差异是造成上风向区域站点CAMx模拟浓度比CMAQ结果偏高的主要原因.CAMx有必要提供更多干沉降的算法供选择,改善光解速率等计算方法可能改善CMAQ臭氧模拟结果.     

Regional source contributions to fine particulate matter of less studied cities in Beijing-Tianjin-Hebei region in 2017

Located in the central area of the North China Plain, the Beijing-Tianjin-Hebei region experiences severe air pollution, especially for Hebei province with five cities among the top 10 cities with the worst air quality nationwide. However, less studies have investigated local and regional contributions to cities in Hebei in comparison to Beijing and Tianjin. In this study, a source-oriented version of the Community Multiscale Air Quality (CMAQ) model is used to quantify inter- and intra-province transport of PM_2.5 in 11 cities within Hebei in 2017. PM_2.5 and its components vary seasonally with high levels in winter and low levels in summer. Local contributions to total PM_2.5 within cities are 23%–61%, while intra-province transport contributes 10%–30%, and inter-province transport contributes 23%–46%, with top contributors of Shandong (4%–22%), Henan (3%–15%) and Shanxi (2%–11%). The primary components in most cities are mainly from local sources (30%–80%), and the secondary components are mainly from inter-province contributions (30%–66%). Local sources have the highest contributions to total PM_2.5 in Shijiazhuang (∼49%), followed by Shanxi (∼12%) and Xingtai (∼7%). Secondary components from local and intra-province emissions are the major cause of heavy pollution events. These results suggest that both local and regional joint control measures with neighboring cities and provinces are necessary for pollution reduction in Hebei cities.     

Simulation of atmospheric aerosols in East Asia using modeling system RAMS-CMAQ： Model evaluation

The modeling system RAMS-CMAQ is applied in this paper to East Asia to simulate the temporo-spatial concentration distributions of atmospheric aerosols. For evaluating its performances, modeled concentrations of aerosols such as sulfate, nitrate, ammonium, black carbon and organic carbon were compared with observations obtained in East Asia on board of two aircrafts in the springtime of 2001. The comparison showed generally good agreement, and, in particular, that the modeling system captured most of the important observed features, including vertical gradients of the aerosols of the Asian outflow over the western Pacific. The evaluation results provide us with much confidence for further use of the modeling system to investigate the transport and transformation processes of atmospheric aerosols over East Asia and to assess their impacts on the Earth＇s radiation budget.