The aim of this thesis is to quantify emissions of selected halogenated refrigerant Ozone Depleting Substances (ODSs) and to make an assessment of some important non-halogenated trace gases, that involve or affect atmospheric O3 chemistry, over megacity Lahore (Pakistan). Ozone Depleting Potential (ODP) and Global Warming Potential (GWP) weighted emissions of halogenated gases such as CFC 11, CFC 12, HCFC 141b and HFC 134a have been quantified in Lahore during 2005-2013. Additionally, anthropogenic emissions, spatial patterns, seasonal variabilities and trends have also been discussed for non-halogenated trace gases such as nitrogen dioxide (NO2), methane (CH4), carbon monoxide (CO), sulphur dioxide (SO2) and carbon dioxide (CO2) and ozone (O3) by using multi satellite and emission inventories data, and air masses trajectories analyses. To estimate ODP and GWP weighted emissions from Lahore, ODSs emissions have been quantified from production, repair/maintenance, and waste/disposal phases. During these phases the cumulative emissions of CFC 11, CFC 12, HCFC 141b and HFC 134a have been estimated to be 1.48 giga-grams which have contributed 293.3 tonnes of ODP (CFC 11-equivalent) and 1.87 mega-tonnes of GWP (CO2-equivalent). Significant declines in ODP (-8.4% yr-1) and GWP (-7.1% yr-1) have been observed during production phase for the period from 2005 to 2013 largely linked to the implementation of Montreal Protocol (1987) phase out programme. Emission Database for Global Atmospheric Research (EDGAR) based anthropogenic emissions of CH4 in Lahore have been recognized as the highest with 27% increase compared to the emissions from neighboring megacities Karachi, Delhi and Faisalabad during 2000-2008. SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) retrieved CH4 total column (TC) is found to be increasing at 4% over Lahore during 2003-2012. SCIAMCHY data also indicate a clear seasonality in CH4 TC with the highest column in August, whereas minimum column is observed in April. OMI observations identify Lahore and its surroundings as a prominent hotspot of tropospheric NO2 (tropo- NO2). A significant increase of 65% has been observed in tropo-NO2 column during 2004-2014. AIRS tropospheric CO (tropo-CO) observations indicate that Lahore has the second highest mean value of tropo-CO column in South Asia after megacity Delhi. An increase of 1.2 % is noted for tropo-CO column over Lahore during 2003-2012. July is found with the highest decadal increase of CO at 10.4% followed by August at 4.9%. It is observed that background CO has greater decrease rate of –0.84% yr–1 than the recent emissions at –0.56% yr–1. OMI Planetary Boundary Layer (PBL) SO2 observations over Lahore reveal 2.4% yr-1 increase in SO2 during 2005-2014 with the highest monthly mean peak in December. EDGAR anthropogenic CO2 emissions and AIRS mid-tropospheric CO2 concentration show increasing trends at 3.1% yr-1 (during 1990-2008) and 1.8 ppm yr-1 (during 2002-2012) respectively. Satellite data suggest that long-range transport of volcanic SO2 from Jabal Al-Tair (Yemen), Dalaffilla (Ethiopia), Nabro (Eritrea) and Mount Etna (Italy) volcanoes has played a significant role in PBL-SO2 enhancements over Lahore. Ozone Monitoring Instrument (OMI) TOC observations over Lahore show a minor increase at 1.1% yr-1 with the highest monthly mean value in April during 2004-2014. This rise is majorly linked to enhancements in ozone precursors and decline in chlorofluorocarbons (CFCs) emissions. This study identifies Lahore as a prominent hotspot of gaseous pollution at regional scale mainly associated with urbanization, industrialization, motorization, large scale crop-residue burning and power generation. The air masses trajectories analyses show that, apart from the transport of gaseous pollution between Lahore and the Indian states of Punjab, it can also be transported from northwestern areas near Pak-Afghan border, Nepal and Arabian Sea.