Spatio-Temporal Variations of Lower Tropospheric Pollutants and Their Relationship With Meteorological Factors in Karachi, Pakistan

Abstract

Purpose: Karachi is the third most populous city globally, inhabiting over 20 million people. Its air quality is hardly ever comprehended despite ever-increasing vehicular and industrial emissions. The present paper investigates the outdoor concentrations of 10 air pollutants, viz. NO, NO2, NOx, SO2, CO, O3, CH4, methane carbon, non-methane hydrocarbons, and total hydrocarbons at three sites of the city and their relationship with meteorological parameters. Method: All ten air pollutants were measured continuously for 24 hours at all three city sites by the Air Quality Monitoring Station, equipped with the Horiba AP-370 series, which has a built-in calibration solenoid valve for calibration simply by connecting the calibration gas. The meteorological parameters were measured simultaneously by the device installed outside the station. The data were then transferred to a computer for analysis. Results: The results demonstrate that these pollutants severely affected the city’s air quality. The annual mean concentrations of both NO2 and SO2 exceeded the WHO guidelines at some sites. The city experiences varied concentrations of major air pollutants because three fuels, viz. diesel, gasoline, and compressed natural gas operate the motor vehicles in this conurbation. The study also correlates the air pollutants with each other and with meteorological factors. All three nitrogen oxides are related to each other at all three sites, with SO2 at Defense Housing Authority, CO at North Nazimabad, and meteorological factors at Sohrab Goth and Defense Housing Authority. Conclusion: The higher air pollution in the city is due to the adoption of lenient vehicular emission standards. Stringent emission standards cannot be adopted because of the non-availability of low or zero sulfur fuel. Moreover, ineffective regulation of exiting standards also contributes to higher vehicular emissions in the city.