Abstract
This paper discussed the urban heat island (UHI) intensity and local air quality by using observational data of project of the System of Air Quality Forecasting and Research (SAFAR) over Delhi during the month of May and December 2013. It is found that UHI magnitudes ~2.2°C and ~1.5°C are formed at the evening traffic hours during May and December respectively. Also, intensity of UHI < 0°C over daytime is referred as Urban Cool Island (UCI) during May and December. The diurnal PM2.5 concentration shows a bimodal pattern with peaks at morning and evening traffic hours during May and December. The planetary boundary layer height (PBLH) values show higher in magnitude during the daytime and lower in magnitude during the night-time. Whereas, the Ground Heat Flux values are lower during the daytime and higher during the night-time. The wind speed shows lower values during the UHI and higher magnitudes during the UCI formation hours. Concentration of PM2.5 and wind speed shows a strong negative correlation during May (r = -0.56, p = 0.002) and December (r = -0.57, p = 0.001) at C V Raman (CVR) site, however, high values in the concentration of PM2.5 during the low wind speed favour the condition for the formation of UCI. The regression analysis indicated that PM2.5 plays a significant role in the daytime cooling and nighttime warming over the urban areas during the low wind speed condition.
Highlights
The urban heat island (UHI) effect is defined as the temperature difference between an urban and the surrounding rural regions
Many studies have mentioned that the association between the UHI phenomenon and air pollution with the favourable conditions such as high temperature, low wind speed, low relative-humidity and cloudless, which are important for UHI development, triggers air pollution episodes [4] [5]
In this study we mainly focus on the hourly Meteorological data of air temperatures and surface concentrations of PM2.5, collected during the December 2013 and 2015 from the two stations, first Sir C V Raman (CVR) Industrial Training Institute (28.73 ̊N, 77.20 ̊E), which is located at north from the center of the city
Summary
The urban heat island (UHI) effect is defined as the temperature difference between an urban and the surrounding rural regions. The structures on ground level, such as walls and roof facets, irrigated gardens, non-irrigated green spaces, lawns and paved areas among others, capture solar radiation to different extents. These natural and man-made structures continuously absorb and store this radiation in the form of heat energy from sunrise till late afternoon. PBLH has been used as a key in weather, climate, and air quality models to determine turbulence mixing, vertical diffusion, convective transport, and atmospheric pollutant deposition [10] [11] As this is one of the critical physical parameters in atmospheric environmental evaluation, studying PBLH’s association with ground level PM2.5 concentration is very important for air pollution and environment quality monitoring. Some earlier studies qualitatively suggest that the UHI may originate from shadow effects in the urban canyon [16], the daytime energy storage in the urban, attenuate the net radiation due to aerosols [17], or the difference in land cover and the available soil moisture altering the surface energy balance
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