Urban Emission Patterns at a Semi-Arid Site in Lahore, Pakistan

摘要

The current research is an attempt to find out diurnal and monthly mean patterns of air pollutants, their interrelationships, and their dominant sources through hourly and monthly data analysis. Lahore is a semi-arid region with low rainfall, hot and humid summers, and cold dry winters. Annually, the highest air quality index (AQI) (132 to 185) is observed from November to February due to inversion at low wind speeds (<1.5 m/s monthly average), low temperature (15 degrees C to 21 degrees C monthly average), and low solar radiation (104 to 140 W m-2 monthly averages). AQI remained low (74 to 85) from June to August due to relatively heavy rain, relatively high wind speed (1.59 to 1.85 monthly averages), dispersion due to high temperatures, high solar radiation, and summer vacations to schools. With an analogous diurnal trend, the AQI remains stumpy in daytime. The high CO/NOx ratio indicates that mobile sources are dominant contributors to NOx; and the low SO2/NOx ratio indicates that point sources are dominant contributors to SO2. CO has a significant positive correlation with NO, NO2, NOx, CH4, SO2, and RH, and a negative correlation with O-3 and temperature. This explains why four-stroke petrol engines are common sources for CO, NO, NO2, and NOx. PM2.5 has a significant positive correlation with SO2, which explains why diesel engines are a common source for PM2.5 and SO2. O-3 has a significant negative correlation with NO, NO2, NOx, CH4, CO, and RH; and has a significant positive correlation with temperature and solar radiation.