Estimating emissions and concentrations of road dust aerosol over China using the GEOS-Chem model

AbstractPaved road dust is one of the most important aerosols in China. The authors estimated road dust emissions using an empirical model (AP-42 model) developed by the U.S. Environmental Protection Agency, and simulated road dust concentrations over China for the years 2006–2011 using the GEOS-Chem model. The annual road dust emissions amount averaged over 2006–2011 is estimated to be 2331.4 kt, with much higher emissions in eastern China than in western China. Because of heavy traffic and a dense road network, emissions are high over Beijing–Tianjin–Tanggu (BTT), Henan Province, and Shandong Province. Meanwhile, emissions are calculated to be 459.1, 112.0, and 102.7 kt, respectively, over BTT, the Pearl River Delta (PRD) region, and the Yangtze River Delta (YRD). Due to the monthly variation of precipitation, road dust emissions over China are simulated to be highest in December and lowest in June. The highest annual mean road dust concentration is simulated to be 14.5 μg m−3 in Beijing. Over 2006–2011...

where EF ij (gram of road dust per vehicle kilometer traveled, g VKT -1 ) is the emission factor for road type i in grid j, and n is 6, which represents 6 road types including freeway, first-class highway, second-class highway, third-class highway, fourth-class highway, and other highway according to the national highway levels of China (CCOT, 2007(CCOT, -2012. A ij (VKT) represents traffic activity rate (vehicle mileage traveled) of road type i in grid j.
The monthly emission factor EF ij of paved road for road type i is calculated as where k is a constant (function of particle size) in g VKT -1 , in this study, we use the AP-42 document-recommended value, k=0.62, for PM 10 ; the value of sL ij is the road surface silt loading for road type i in grid j (g m -2 ); W ij stands for the average weight (tons) of the vehicles traveling the road for road type i in grid j; Pr j is the number of "wet" days with at least 0.254mm (0.01 in) of precipitation during the averaging period in grid j which is calculated from the meteorological field; and N is the number of days in the averaging period (e.g., 365 for annual).  (Yanmin et al., 2006), and Sichuan Basin (SCB, 28°-31.5°N, 102.5°-107.5°E) (Yang et al., 2015). For other areas, we use the average values of sL ij and W ij from four areas above.
The value of A ij (VKT) can be determined by traffic flow and road length (Peng et al., 2013): where F ij (h -1 ) is the traffic flow of road type i in grid j; L ij (km) represents the length of road type i in grid j, and T (h) is the number of hours in the period (e.g., 24 for daily). The transport emissions of HTAP_V2 dataset and traffic flow information in previous studies are used to determine the monthly value of F ij of road type i in grid j.
Firstly, we defined the traffic flow of road type i in grid j, F ij as: where the value of R i represents the ratio of traffic flow for road type i to the total traffic flow; and P j represents the ratio of traffic flow in grid j to the total traffic flow in China; total F (h -1 ) represents total traffic flow of China.
R i can be calculated from: and SCB by the sum of all road types. The values for the six variables describe above can be derived from previous studies (Yanmin et al., 2006;Peng et al., 2013;Yang et al., 2015).
The defined ratio P j is derived from HTAP_V2 dataset (http://edgar.jrc.ec.europa.eu/htap_v2/) which calculated the transport emission data for different pollutant species (such as SO 2 , NO x , and so on) by using traffic activity data and emission factors (Zheng et al., 2014). Here we assume that the ratio of transport emission in each grid to the total transport emission is equal to the ratio of traffic flow, which is described as P j . So we can calculate P j from the formula as follows: where total HT E is the total transport emission from HTAP_V2 dataset for all grids in China, and j HT E is the transport emission of grid j.
Next, the traffic flow for all grids is calculated by dividing traffic flow in PRD, YRD, and SCB by their related ratio P j , where F PRD , F YRD , and F SCB represent the total traffic flow in PRD, YRD, and SCB; and P PRD , P YRD , and P SCB are the transport flow ratios over three areas. Lastly, we get the road dust emission at each grid cell.