Impacts Of Anthropogenic Aerosols On The Climate Over Regions With Different Scales

Anthropogenic aerosols’ impact on environment and climate currently is one of the most concerned issues as the air quality has been exacerbated. Aerosols could affect the climate both locally and globally. As for the study of impacts on regional climate due to aerosols, it usually focuses on the radiativce forcing, changes in surface temperature and precipitation, while as for urban and surrounding areas, it could focus on the aerosols’ impact on the differences in dynamic and thermodynamic characters between urban and suburban regions. Researches on the climate effects due to aerosols over regions with regional scales are very abundant, whereas those on the climate impacts over urban regions are scarce. In this dissertation, two meteorology-chemistry coupled models, RIEMS2.0and WRF/Chem, respectively, were used to simulate the impacts on climate due to anthropogenic aerosols over regions with two different scales. RIEMS2.0was used to simulate anthropogenic sulfate and carbonaceous aerosols’ climate effects in East Asia under different mixing assumptions and WRF/Chem was used to study the climate effects due to anthropogenic sulfate, nitrate, and carbonaceous aerosols over Nanjing. Some interesting results were found as follows:(1) Three mixing assumptions for anthropogenic sulfate and carbonaceous aerosols, which were internally mixed (IM), externally mixed (EM), and partial internally mixed (IEM), were set up in RIEMS2.0to simulate their different climate effects in East Asia during the entire year of2006. The results indicated that the mass concentration of anthropogenic sulfate was significantly sensitive to mixing assumptions while carbonaceous aerosols were much less sensitive to the mixing types. Modeled results were compared with observations in a variety of sites in East Asia. It was found that the simulated concentrations of sulfate and carbonaceous aerosols were in accord with the observations in terms of magnitude. The simulated aerosols concentrations in IM case were closest to observed values.(2) There were also significant differences in radiative forcing and climate effect over East Asia between three mixing assumptions. It was found that the annual averages of radiative forcing due to anthropogenic aerosols were highest in IM case whereas smallest in EM case. However, the changes in annual average of surface temperature and in annual precipitation due to aerosols were negative in all of the three cases. The decrease of surface temperature was most significant in IM case but slightest in EM case. Meanwhile, for IEM case, the decrease in precipitation was largest and for the EM case, it was smallest.(3) Three nested domains were simulated with the usage of WRF/Chem, the largest of which covered most of the regions in China and most inside domain was Nanjing and its surrounding regions. The simulated period was also the entire year of2006and the simulated categories of aerosols were containing anthropogenic sulfate, black carbon, organic carbon (both primary and secondary), and nitrate. Simulated results indicated that there was a significant difference in aerosol concentrations between urban and suburban areas. Anthropogenic aerosols were highly concentrated in the main urban area of Nanjing, Qixia and Northern region of Yangtze river, both of which were industrial regions. Yangzhou and Zhenjiang, two cities lying alongside the Yangtze river, and two regions of Maanshan across the Yangtze river were also with relatively high concentrations of aerosols. Aerosols in immediate suburban regions were approximately with half of the concentrations in urban and concentrations in rural regions were much less than those in urban area.(4) There is a seasonal variation in monthly aerosol concentrations in Nanjing, with a highest value in October and a smallest one in Janary. Aerosols were transported from urban area to suburban region and organic aerosol was with most significant transports whereas black carbon was with the slightest ones. The contribution of total anthropogenic aerosols (TA) to PM2.5ranged from58%to70%and the contribution of black carbon was smallest while the one of organic carbon was largest.(5) During April and July of2006, the urban heat island effect was significant in Nanjing. Anthropogenic aerosols led decreases in surface temperature, a larger one in urban area and a smaller one in suburban, which slightly offset the heat island effect in Nanjing. The magnitude of heat island most significantly decreased in October. The latent heat fluxes in urban were smaller than in suburban regions, however, both of which were with similar daily variation. Latent heat fluxes decreased in Nanjing due to anthropogenic aerosols and the divergences between urban and suburban decreased as well. Contrarily, the sensitive heat fluxes were larger in urban, where also with a more severe decrease in sensitive heat due to aerosols, than in suburban regions. Additionally, dry island effect was also occurring in Nanjing, which was most significant in July and slightest in January. Additionally, humidity increased in both urban and suburban regions. However, the increase in urban was larger than that in suburban region, which weakened the dry island effect in Nanjing.(6) The divergence in the height of boundary layer between urban and suburban regions was larger during daytime and smaller in nighttime. The averages of boundary layer height decreased simultaneously in urban and suburban regions due to aerosols’ effects, with maxima both in October. In average, the divergence between urban and suburban regions slightly decreased after considering anthropogenic aerosols.