The impact of aerosol on MODIS cloud detection and property retrieval in seriously polluted East China.

Previous researches proved that aerosols have a significant influence on the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observation. In East China, this impact is much greater and special compared with other regions because of the frequent haze pollution. This study evaluated the impact of aerosols on cloud detection, cloud top height (CTH) and cloud optical thickness (COT) retrieval in East China primarily using the MODIS and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observation, combined with a cloud detection rectification algorithm. The results showed that, in haze weather, MODIS misjudged large-scale of dense aerosols as "clouds", which increased the observed cloud cover by 0.4 to 0.6 in the most seriously polluted regions. Compared with the clear condition, high aerosol loading with AOD >2 would increase the misjudgment possibility by 35%. Another influence is that MODIS has a 30% higher possibility to obtain an over low CTH of high and thin clouds, and overestimate the COT of thin ice clouds by 2.15 to 3.74 under serious air pollution. Further analyzes found that the cloud detection and COT retrieval was mainly influenced by the dense aerosols, while the CTH retrieval is vulnerable to both thin and dense aerosol. This study made a quantitative measurement of the aerosol influence on MODIS cloud observation, and first made a deep explanation for the effect of air pollution density.

[Column-integrated Aerosol Optical Properties Determined Using Ground-based Sun Photometry Measurements in the Hangzhou Region].

To investigate the optical properties of aerosols in the Hangzhou region (Hangzhou, Tonglu, Jiande, and Chun'an), the aerosol optical depth (AOD), Ångström exponent (AE), single scattering albedo (SSA), and aerosol size distribution (ASD) were measured using CIMEL sun-photometers in 2012. The results showed that the annual average values of AOD440nm in Hangzhou, Tonglu, Jiande, and Chun'an were 0.94±0.16, 0.84±0.17, 0.82±0.22, and 0.71±0.20, respectively. The values generally decreased from the northeast to the southwest, and represented one of highest AOD districts in the Yangtze River Delta, China. The annual average values of AE440-870nm were 1.24±0.12, 1.19±0.17, 1.06±0.04, and 1.04±0.10, respectively, indicating that particles with small average effective radii were predominant. The relatively lower AE values in March and April were generally attributed to the long-range transport of dust aerosols from Northwest China. Obvious diurnal variations in the AOD were found in Hangzhou, Tonglu, and Jiande, but not in Chun'an. An average fine-mode effective radius of~0.15 µm was observed in spring, autumn, and winter, while a value of~0.25 µm was observed in summer, in conjunction with aerosol hygroscopic growth. An average coarse-mode effective radius of~2.94 µm was observed in summer, autumn, and winter, which was higher than the value in spring. The annual average values of SSA440nm were 0.91±0.01, 0.92±0.03, 0.92±0.02, 0.93±0.02, respectively, indicating that the particles had relatively strong to moderate absorption. Characterization of the aerosol types showed the predominance of biomass burning and urban industrial type aerosols in Hangzhou, while mixed type aerosols were observed in Tonglu, Jiande, and Chun'an.

[Observation study on aerosol optical properties and radiative forcing using the ground-based and satellite remote sensing at background station during the regional pollution episodes].

The significant effect of anthropogenic pollutants transportation on the physical and optical properties of regional background atmospheric aerosol was studied by using ground-based and satellite remote sensing data obtained at the atmospheric background station (Shangdianzi, Beijing) of North China during October 1 to 15 in 2011. The aerosol mass concentration and reactive gases concentration increased obviously during periods of October 4-5, October 7-9, and October 11-12. Comparing with the background period of October 1-3, volume concentration increased by a factor of 3-6 for reactive gases such as NO(x), and CO, and a factor of 10-20 for SO2. Mass concentration of PM2.5 was about 200 microg x m(-3) on October 9. During haze period, the AOD at 500 nm varied between 0.60 to 1.00. The single scattering albedo (SSA) was lower than 0.88. And the black carbon concentration increased 4-8 times, which suggested the aerosol absorption was very strong during this pollution episode. The absorption of aerosol particles could cause 100-400 W x m(-2) increase of atmospheric radiation. The surface radiation decreased by about 100-300 W x m(-2) due to the aerosol scattering and absorption. This could cause higher stability of atmosphere, which will significantly affect the cloud and precipitation, and thus the regional weather and climate.