ABSTRACT
Based on the MYD04_L2_C006 dataset gained from Moderate resolution imaging spectroradiometer MODIS Level 2 at 10 km resolution of NASA's EOS (Earth Observing System) from 2006 to 2015, the aerosol optical depths (AODs) for 10 years under the condition of mild above atmospheric pollution (including mild) were analyzed for Urumqi City. The results showed that the average AODs in Urumqi were unimodally distribution over the 10 years. From January to April, the AODs gradually increased. During a year, the annual peak of 0.37±0.19 was in April, and the lowest value of 0.22±0.20 was in October. Owing to the frequent occurrence of dust weather conditions in spring, the largest seasonal variation of AOD was in spring, as the air pollution in the entire area was very serious, followed by summer and winter, with the smallest in autumn. In addition, the urban area was the high AOD value area in Urumqi, as its air pollution was more severe than that in the suburbs. The average value of AOD during the 10 years was 0.293. The highest value of AOD was 0.33 in 2006, and the lowest value of 0.24 was in 2008, which declined to 23.3% of that in 2007. The annual change in AOD in Urumqi over the 10 years rose steadily. Compared with previous studies, the lowest and highest values were both higher to different degrees. Despite the deduction trend in 2015, air pollution in Urumqi was serious in the studied decade, and thus control of such needs to be strengthened.
ABSTRACT
The variations of black carbon (BC) mass concentration in Shanghai are analyzed and discussed by using hourly averaged data monitored continuously at Shanghai Urban Environmental Meteorological Center from January 2008 to December 2012. The results show that the annual mean mass concentration of BC decreased from (4 045.3 +/- 3 375.4) ng x m(-3) in 2008 to (2 766.2 +/- 2 078.9) ng x m(-3) in 2012, and the annual changes are 2.3%, - 6.5%, -18.7% and -12.1%, respectively. The yearly averaged BC mass concentration in Shanghai is on the low side of middle-level compared with other mega-cities of China. According to the test data,the highest monthly averaged concentration of BC appeared in November and December,which were 5 426.6 ng x m(-3) and 5 365.3 ng x m(-3), respectively,and then in January, June and October, which were 4402.5, 3763.3 and 3412.7 ng x m(-3), respectively. The diurnal cycles of the BC mass concentration show that there are two obvious peaks during morning 07:00-10:00 and during evening 18:00-22:00 Beijing time (BT), and the first peak was higher than the second on weekdays, but opposite on weekends and holidays. The daily mean mass concentration of BC was 9% higher on weekdays than on weekends and holidays. In addition, an empirical equation is obtained for daily BC concentration estimation and prediction using all the effective test data during the 5-year observation period and employing the regression analysis.
Subject(s)
Air Pollutants/analysis , Environmental Monitoring , Soot/analysis , Carbon/analysis , China , Cities , SeasonsABSTRACT
The performance of electrostatic precipitators (ESPs) is affected by factors such as the geometric configurations, the charge conditions and the fluid flow and the particulate flow characteristics. In this paper, a theoretical model is presented to study the particle transport in the collecting channel of a laboratory-scale single-stage multi-wire ESP. The employed model is validated by comparing its predictions with published experimental data and other theoretical prediction models. The particle size distribution is represented by a lognormal function, and the effects of the geometric parameters of ESPs on collection efficiency under different charge conditions are calculated and analyzed. The results confirm that the collection efficiency of ESPs can be enhanced by employing large-sized corona wire under the same average current density or corona power ratio, while the opposite rule is shown under the same electric field strength.
