The United States experienced a sharp increase in unconventional natural gas (UNG) development due to the technological development of hydraulic fracturing ("fracking"). The objective of this study is to investigate the effect of unconventional natural gas development activities on local air quality as observed at an active Marcellus Shale well pad at the Marcellus Shale Energy and Environment Laboratory (MSEEL) in Morgantown, Western Virginia, USA. Using an ambient air monitoring laboratory, continuous sampling started in September 2015 during horizontal drilling and ended in February 2016 when wells were in production. High resolution data were collected for the following air quality contaminants: volatile organic compounds (VOCs), ozone (O), methane (CH), nitrogen oxides (NO and NO), carbon dioxide, (CO), as well as typical meteorological parameters (wind speed/direction, temperature, relative humidity, and barometric pressure). Positive Matrix Factorization (PMF), a multivariate factor analysis tool, was used to identify possible sources of these pollutants (factor profiles) and determine the contribution of those sources to the air quality at the site. The results of the PMF analysis for well pad development phases indicate that there are three potential factor profiles impacting air quality at the site: natural gas, regional transport/photochemistry, and engine emissions. There is a significant contribution of pollutants during horizontal drilling stage to natural gas factor. The model outcomes show that there is an increasing contribution to engine emission factor over different well pad drilling through production phases. Moreover, model results suggest that the major contributions to the regional transport/photochemistry factor occurred during horizontal drilling and drillout stages.