Effects of urban land expansion on the regional meteorology and air quality of eastern China
Rapid urbanization throughout eastern China is imposing an irreversible effect on local climate and air quality. In this paper, we examine the response of a range of meteorological and air quality indicators to urbanization. Our study uses the Weather Research and Forecasting model coupled with chem...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/8597/2015/acp-15-8597-2015.pdf |
| Summary: | Rapid urbanization throughout eastern China is
imposing an irreversible effect on local climate and air quality. In this
paper, we examine the response of a range of meteorological and air quality
indicators to urbanization. Our study uses the Weather Research and
Forecasting model coupled with chemistry (WRF/Chem) to simulate the climate
and air quality impacts of four hypothetical urbanization scenarios with
fixed surface pollutant emissions during the month of July from 2008 to 2012.
An improved integrated process rate (IPR) analysis scheme is implemented in
WRF/Chem to investigate the mechanisms behind the forcing–response
relationship at the process level. For all years, as urban land area expands,
concentrations of CO, elemental carbon (EC), and particulate matter with
aerodynamic diameter less than 2.5 microns (PM<sub>2.5</sub>) tend to decrease near
the surface (below ~ 500 m), but increase at higher altitudes
(1–3 km), resulting in a reduced vertical concentration gradient. On the
other hand, the O<sub>3</sub> burden, averaged over all newly urbanized grid cells,
consistently increases from the surface to a height of about 4 km.
Sensitivity tests show that the responses of pollutant concentrations to the
spatial extent of urbanization are nearly linear near the surface, but
nonlinear at higher altitudes. Over eastern China, each 10 % increase in
nearby urban land coverage on average leads to a decrease of approximately
2 % in surface concentrations for CO, EC, and PM<sub>2.5</sub>, while for
O<sub>3</sub> an increase of about 1 % is simulated. At 800 hPa, pollutants'
concentrations tend to increase even more rapidly with
an increase in nearby urban land coverage. This
indicates that as large tracts of new urban land emerge, the influence of
urban expansion on meteorology and air pollution would be significantly
amplified. IPR analysis reveals the contribution of individual atmospheric
processes to pollutants' concentration changes. It indicates that, for
primary pollutants, the enhanced sink (source) caused by turbulent mixing and
vertical advection in the lower (upper) atmosphere could be a key factor in
changes to simulated vertical profiles. The evolution of secondary pollutants
is further influenced by the upward relocation of precursors that impact
gas-phase chemistry for O<sub>3</sub> and aerosol processes for PM<sub>2.5</sub>. Our
study indicates that dense urbanization has a moderate dilution effect on
surface primary airborne contaminants, but may intensify severe haze and
ozone pollution if local emissions are not well controlled. |
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| ISSN: | 1680-7316 1680-7324 |