Contribution of source emissions in the air pollution modeling - a WRF/Chem case study

Document Type : Research

Authors

1 Atmospheric Science and Meteorological Research Center (ASMERC)

2 ASMERC

3 Associate Professor of Atmospheric Science and Meteorological Research Center (ASMERC)

Abstract

Between 16 and 21 December 2017, several megacities in Iran, such as Tehran, Tabriz,, and Isfahan experienced a considerable increase in air pollutants. In this article, using the HTAP_v2 global emissions data, and by the WRF/Chem modeling system, the concentration time series of some important gaseous criteria pollutants, including NO2, SO2, and CO have been simulated. The variations of the time series of the pollutants and the comparisons of the results in Tehran with the measurement data showed that although the WRF/Chem simulations in Tehran presented considerable over-estimations, but the model’s performance with regard to the time variations of the concentrations of the gaseous agents over the polluted episode is acceptable, and therefore, could be considered in the operational air quality systems. Since emission data are not available for many metropolitan areas over Iran, the HTAP_v2 global dataset could be used as the emissions data with reliable accuracy for the numerical air quality models. Sea surface pressure during 16 to 21 of December 2017 indicates the settling of high pressure systems from north east of Iran, which gradually intensifies over north-west and central parts of Iran, about 4 hpa. In other words, it increases from 1024 hpa in 16 December to 1028 hpa in 21 December. Variations of surface humidity over the study period are not significant. Dew point deficit over the north-west is about 2 and over the central parts of Iran is about 7 °C. Furthermore, 10 m wind speed does not show considerable variation and is generally less than 10 knots. Using the ECMWF meteorological reanalysis data as the initial and boundary conditions, the model WRF/Chem has been run with two domains. Quantitative comparisons between the WRF/Chem results and the measurements show a considerable overestimation for Tehran. Considering the increase of the pollutants over the beginning and the middle of simulation period and its decreasing over the end of the simulation period, the temporal variations of the model results, especially for Tehran, present a good agreement with regard to the variations of the pollutants for this episode. Regarding the WRF/Chem results which have been run by the HTAP global emission data, these dataset are accurate enough to be used in the regional models. Therefore, for the mesoscale simulations (less than 1000 km), the HTAP global dataset provide reliable and valid emissions data which are highly valuable especially for those regions and urban areas without any local measured emissions data. Although the WRF/Chem model is a regional model, the model’s grid points could be set with a high spatial resolution to simulate the urban air pollutants. Since the model WRF/Chem in this study has shown a good performance in the estimation of the variations in the air pollutant concentrations over the urban areas, this capability could be used to set up operational air quality models for the urban areas, as an air quality warning and advisory system. If there are national emissions data, they could be used instead of the global emissions to reach more accurate model results in air quality modeling.

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