Characteristics and Sources of Organic Aerosol Near Oil and Natural Gas Drilling Operations

The Bakken Air Quality Study (BAQS) was conducted in the winters of 2013 and 2014 to investigate the air quality impacts from oil and natural gas extraction in the Bakken formation region where the use of horizontal drilling and hydraulic fracturing has increased significantly in the last decade.  During BAQS, comprehensive aerosol composition measurements revealed regional episodes of elevated aerosol concentrations dominated by inorganic species ammonium sulfate and ammonium nitrate.  These elevated aerosol episodes are correlated with periods of stagnation and VOC markers of oil and natural gas operations, suggesting that local oil and gas emissions impact aerosol concentrations.  Organic aerosol, comprising an average 31% of the total submicron aerosol, has a smaller but still significant contribution to high aerosol episodes and will be investigated in this study.  Organic aerosol measurements were made during the second BAQS study using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer.  Positive matrix factorization (PMF) analysis of the organic aerosol identified a low volatility oxidized organic aerosol factor (LV-OOA) and a hydrocarbon-like organic aerosol (HOA), making up 80% and 20% of the total organic aerosol, respectively.  HOA is correlated with nitrogen oxides and light hydrocarbons which indicate their source is likely local oil and gas related activities.  LV-OOA is correlated with ammonium nitrate, whose concentrations are enhanced during periods of light wind speeds and stagnation within the region of oil and gas development.  The oxidation and sources of the LV-OOA is investigated further using elemental ratios, meteorological variables and other aerosol and gas measurements.  Calculations of reconstructed aerosol scattering indicate that organic aerosol is a significant component to scattering.  The role of organic aerosol to the observed wintertime haze events is also discussed.