Abstract
The sensitivities of meteorological and chemical predictions to urban effects over four major North American cities are investigated using the high-resolution (2.5-km) Environment and Climate Change Canada’s air quality model with the Town Energy Balance (TEB) scheme. Comparisons between the model simulation results with and without the TEB effect show that urbanization has great impacts on surface heat fluxes, vertical diffusivity, air temperature, humidity, atmospheric boundary layer height, land-lake circulation, air pollutants concentrations and Air Quality Health Index. The impacts have strong diurnal variabilities, and are very different in summer and winter. While the diurnal variations of the impacts share some similarities over each city, the magnitudes can be very different. The underlying mechanisms of the impacts are investigated. The TEB impacts on the predictions of meteorological and air pollutants over Toronto are evaluated against ground-based observations. The results show that the TEB scheme leads to a great improvement in biases and root-mean-square deviations in temperature and humidity predictions in downtown, uptown and suburban areas in the early morning and nighttime. The scheme also leads to a big improvement of predictions of NOx, PM2.5 and ground-level ozone in the downtown, uptown and industrial areas in the early morning and nighttime.
Highlights
Rapid urbanization around the world leads to significant changes in urban settings [1,2].The residential, industrial and commercial buildings and paved streets in urban areas significantly change the urban land use and land cover, and consequentially change the radiation balance, thermal distribution, and aerodynamics in urban areas [3,4,5]
While the results in preceding sections show robust responses of both meteorological and chemical fields to the Town Energy Balance (TEB) scheme in urban areas, and the features of the responses can be interpreted by analytical results, these impacts still need to be evaluated against observations to justify the improvements by the TEB scheme
Observations used for the evaluation are from Mesonet Automated Land Stations Observations, a high-resolution monitoring system across Southern Ontario developed by the Environment and Climate Change Canada (ECCC) by adding compact stations, 10 ATMOS stations, and three standard automated MSC Auto8 stations to the existing observation networks during the Pan, and Para-pan American Games period in 2015
Summary
Rapid urbanization around the world leads to significant changes in urban settings [1,2]. The waste heat produced by heating or cooling buildings and by vehicles modifies the urban surface energy balance These changes in urban settings, along with the daily anthropogenic activities in urban areas, impose great impacts on urban meteorology and air quality [6]. In spite of the challenges mentioned above, the growing needs for accurate predictions of urban meteorology and air quality for the comfort, safety and health of urban dwellers, along with the advent of powerful supercomputers and the advanced geographic information systems, have motivated numerous studies on the urbanization impact on the urban meteorological and chemical environment In these studies, the urbanized high resolution numerical models have been widely employed to simulate the complicated physical, dynamical and chemical interactions between urban canopy and the atmosphere in the UBL [21,22,23,24,25,26,27,28,29].
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