Source Apportionment of the Air Quality on Sable Island
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Air pollution can have varying health and environmental impacts which are not limited to the point of release, making it important to identify and quantify sources of air pollution and their fate and transport globally. Most studies are conducted in urban areas with few studies taking place at sea or near oil and gas (O&G) production facilities, resulting in a paucity of data. This study aims to examine the different sources of air pollution affecting the air quality on Sable Island, a remote marine site, with the aim of better understanding the impacts of emissions from nearby offshore O&G activities and continental outflow. Air pollution data obtained from Sable Island between May 7th and October 30th of 2013 was used to perform statistical analysis, source apportionment, and meteorological analysis. The models used to identify and quantify sources of air pollution included the National Oceanic and Atmospheric Administration (NOAA) HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the United States Environmental Protection Agency (USEPA) Positive Matrix Factorization (PMF) model v 22.214.171.124. The air pollutants measured and their temporal resolution were non-methane hydrocarbons (NMHCs), black carbon (BC), hydrogen sulfide (H2S), mono-nitrogen oxides (NOx), nitrogen oxide (NO), nitrogen dioxide (NO2), ozone (O3), particulate matter with a median aerodynamic diamer less than or equal to 2.5 microns (PM2.5), and sulphur dioxide (SO2). NMHCs and BC measurements were averaged every 5 minutes while the remaining data was averaged hourly. The average concentration of O3 (30.4 ppb) was below the annual average concentration of O3 in ambient air in Canada which was 33 ppb in 2011 (Environment Canada, 2013) while all of the average and maximum concentrations for pollutants governed by The Air Quality Regulations from Nova Scotia Environment (including O3) fell below maximum permissible levels. The mean values (min:max) for NMHC, BC, PM2.5, SO2, H2S, O3, NO, NOx, and NO2 were 0.034 ppm (0.0 : 1.13), 0.092 µg/m3 (0.0 : 13), 14.1 µg/m3 (0 : 43), 0.168 ppb (0.0 : 3), 0.361ppb (0.0 : 13.7), 30.4 ppb (8.24 : 61.1), 2.17 ppb (0.0 : 3.5), 1.12 ppb (0.0 : 28.7), 0.998 ppb (0.0 : 14.6). During this study, a new gas production facility came on line on July 22nd 2013. Significant differences (P<0.05) between concentrations of BC, PM2.5, SO2, H2S, O3, NO, NOx, and NO2 were seen after July 22nd 2013. The median values and upper percentiles for BC, PM2.5, NO, and NOx show decreases after July 22nd, while those for SO2, H2S, and NO2 show increases. Due to the strong correlation of SO2 and H2S with offshore oil and gas activities found through PMF modelling and a spearman rank order correlation this implies the new off-shore gas production did have an impact on the air quality on Sable Island. The PMF model run identified 4 factors contributing to the air quality on Sable Island but source contributions could not be determined due to insufficient PM2.5 and VOC speciation data. Long range transport, off-gassing from offshore O&G activities (with contributions from phytoplankton blooms), flaring, and on-site combustion were the sources associated with these 4 factors. It was recommended that sampling on Sable Island continue as further characterization of the air quality would be beneficial to more fully understanding sources and sinks of air pollution on the island and the surrounding Scotian Shelf.