MONITORING FORMALDEHYDE CONCENTRATION OVER ISLAMABAD USING GROUND BASED AND SATELLITE OBSERVATIONS

Abstract

In Pakistan as well as in many other countries, traffic is one of the most important source of high pollution levels in cities and thereby also high exposure of the population in the ambient environment. Formaldehyde is an intermediate product in the oxidation pathways of nonmethane hydrocarbons emitted by anthropogenic and biogenic activities. This study is designed to monitor the HCHO concentrations over Islamabad, Pakistan. Mini MAX-DOAS (Multi Axis – Differential Optical Absorption Spectroscopy) instrument was used to perform ground-based measurements at IESE (Institute of Environmental Sciences and Engineering), NUST (National University of Sciences and Technology), Islamabad (33.6416° N, 72.9835° E) Pakistan. The spectra were acquired for a period of six months i.e. October 2013-March 2014. Analysis was performed to retrieve HCHO Differential Slant Column Densities (DSCD). Tropospheric vertical column densities (VCD) of HCHO over Islamabad were derived from measured DSCD by using geometric air mass factor approach. Mean Tropospheric HCHO VCDs were found to be 4.32 × 1016 molecules/cm2 . Satellite observations from Ozone Monitoring Instrument (OMI) were used for comparison with the ground based observations from Mini MAX-DOAS. Tropospheric HCHO VCDs derived from ground-based mini MAX-DOAS measurement showed a good agreement with the satellite observations over Islamabad, Pakistan. However, satellite observations underestimate the concentration of HCHO by 1 degree. Further, wind data was used to find out the possible pollution corridor in NUST. Kashmir highway and Golra Moar were the main pathways for pollution.