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In mid‐August 2009, ground‐based lidar networks on both sides of the Pacific Basin detected an elevated dust layer. A combined analysis by ground‐based lidars, space‐borne lidar CALIOP, and numerical models revealed that dust particles emitted in the Taklimakan Desert were transported across the Pacific Ocean in 12 to 13 days. This was the first evidence of summertime trans‐Pacific transport of Asian dust from the Taklimakan Desert. A large‐scale dust storm occurred in the Taklimakan Desert during 12–16 August due to a strong surface wind accompanied by a cold front. Many dust particles were lifted up into the free atmosphere by the upslope wind formed by the steep slope of the surrounding mountains. This dust injection process was analogous to that for springtime cases. The Taklimakan dust was then transported eastward at 6–8 km altitude. This high transport altitude allowed the Taklimakan Dust to be transported beyond the Pacific Ocean without the effect of the southeasterly outflow of the summertime Pacific high. The wind field anomaly at 500 hPa in mid‐August 2009 shows increases of northwesterly winds driven by SE–NW pressure gradients around 110–140°E and 180–140°W, indicating that the pressure pattern during the dust event favored the trans‐Pacific transport.

The NASA space-borne Mie-lidar system CALIPSO/CALIOP revealed that multiple large Asian dust layers with a horizontal scale of 2000–3000 km reached North America, occupying the full troposphere, in April 2010. This kind of dust layer transport has not been reported before. Our analysis of CALIOP data and global aerosol model results revealed that frequent dust emissions occurred in northwestern China because of stronger-than-average near-surface winds, and that strong stable westerly winds carried the Asian dust from northwestern China to the central Pacific Ocean. A negative pressure anomaly was located in the eastern Pacific Ocean, and the main dust transport path was split into two branches: a northern path and a southern path over North America. Northern-path dust was trapped and stagnant for a longer time than southern path dust and finally subsided under a high pressure system. Dust along the southern path reached the central US. These complex conditions resulted in a multi-layered structure of dust over North America

Abstract. The impact of open crop residual burning on O3, CO, Black Carbons (BC), and Organic Carbons (OC) concentrations over Central Eastern China (CEC) during the Mount Tai Experiment 2006 (MTX2006) was evaluated using the regional chemical transport model, the Models-3 Community Multiscale Air Quality Modeling System (CMAQ). To investigate these pollutants during the MTX2006 period in June, daily gridded emissions from open crop residual burning were developed based on a bottom-up methodology and using land cover and hotspot information from satellites. This model system which involves daily emissions from open biomass burning, captured monthly-averaged observed concentrations and day-to-day variations in the patterns of O3, CO, BC, and OC with good correlation coefficients between models and observations, ranging from 0.54 to 0.66. These results were significantly improved from those using annual emissions. For monthly-averaged O3, the simulated concentration of 81.5 ppbv was close to the observed concentration (82.5 ppbv). The period of MTX2006 was roughly divided into two parts: 1) polluted days with heavy open crop residual burning in the first half of June; 2) cleaner days with negligible field burning in the latter half of June. Additionally, the first half of June was defined by two high pollution episodes during 5–7 and 12–13 June, and a relatively cleaner episode during 8–10 June between these two high pollution episodes. In the first polluted episode, this model captured high O3, CO, BC, and OC concentrations at the summit of Mount Tai which were affected by open crop residual burning in the south of CEC and northward transport. For this episode, the impacts from open crop residual burning were 12% for O3, 35% for CO, 56% for BC, and 80% for OC over CEC. The daily emissions from open crop residual burning were an essential factor to evaluate the pollutants during the MTX2006. These emissions have a large impact not only on primary pollutants but also on secondly pollutions, such as O3, in the first half of June over northeastern Asia. On the other hand, this model did not capture the second polluted episode and underestimated observed CO and BC. Improvements of both anthropogenic and open burning emissions and CO inflow from model boundary are necessary to improve both anthropogenic and open burning emissions and CO inflow to evaluate the pollutants using this model.

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