Quantifying the Impact of Urban Expansion on East Asian Aerosol Loadings: Models amd Measurements across Urban and Meso scales

The short lifetime and heterogeneous distribution of Black Carbon (BC), Organic Carbon (OC), Sulfate, Nitrate, and other aerosols in the atmosphere leads to complex impacts on radiative forcing, climate, and health, and complicates analysis of its atmospheric processing and emissions. However, due to intense and changing levels of emissions as well as highly non-linear chemical processing, in particular both occurring in urbanized regions, the concentrations of these species and thus their impacts are not well known. Urban areas consist of the majority of the emissions of these species and their precursors, yet due to urban and economic expansion, the spatial and temporal profiles of these species are changing. In some cases, increasing, while in others decreasing, both in space and time. Due to these complexities, our current understanding, especially for huge megacities and intensely urban areas is still quite limited.

Two recent papers have estimated the global and regional emissions of BC using advanced statistical and computational methods. One used a Kalman Filter, including data from AERONET, NOAA, and other ground-based sources, to estimate global emissions of 17.8+/-5.6 Tg BC/year (with the increase largest in East and Southeast Asia, regions with rapid urban, industrial, and economic expansion). The second used remotely sensed measurements from MISR and a variance maximizing technique, uniquely quantifying fire and urban sources in Southeast Asia, as well as their large year-to-year variability over the past 15 years, leading to increases from 10% to 150%. These emissions, when run a state-of-the art modelling system of chemistry, physics, transport, removal, radiation, and climate, match 140 ground stations and satellites better in both space and time.

New work now incorporates both new measurements from additional sources, to constrain OC and Nitrate, including satellite and surface measurements. This new approach is shown to be identify new source regions of emissions, many of which were previously non-urbanized. In addition, the use of new models run under conditions including both missing local sources from regions such as the expanded urban areas in Southeast Asia, Guangxi, Guangdong, and Fujian, and advanced chemical and aerosol routines, allow for a comprehensive analysis to be performed. The impacts of transport of species, both on the Regional and Continental scale are included. It is shown to be important for identification of the peaks found throughout populated areas both in this part of the world, as well as in areas as far away as Korea and Taiwan.

Results specific to Southern China and East Asia demonstrate the additional importance of the climate, as both inter- and intra-annual variations are identified. Such knowledge can allow us to better understand the consequences and impacts of the rapid ongoing urbanization occurring in these regions, and allow for better planning to curtail the impacts of such changes as we move into the future.