Impacts of Arctic oil field NO_<i>x</i> emissions on downwind bromine chemistry: insights from 5 years of MAX-DOAS observations

Oil and gas production is a substantial source of nitrogen oxides to the atmosphere, with significant impacts particularly in remote regions without other large local NO_<i>x</i> sources. In the Arctic, these emissions impact regional halogen and HO_<i>x</i> chemistry, altering the oxidation of atmospheric pollutants. In this work we utilize Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) NO₂ and BrO measurements at Utqiaġvik, Alaska, from 2012 to 2016. During the spring months when atmospheric bromine chemistry is most prevalent, we find 8% of observations are impacted by observed NO₂ differential slant column densities (dSCDs) over 5 × 10¹⁵ molecules per cm², which we classify as polluted. Of this fraction, approximately half can be attributed to sources outside the immediate vicinity of Utqiaġvik. During these polluted times, observed BrO lower tropospheric column densities (LT-VCDs) are 60% lower on average than those retrieved during non-polluted times. During times when the local wind direction corresponds with a large collection of oil and gas extraction facilities approximately 300 km southeast of Utqiaġvik, observed BrO LT-VCDs were 30% lower than clean air times. These observations show that current oil and gas operations in the Arctic are impacting the natural atmospheric photochemical processes.