Abstract
Ozone (O3), alkyl nitrates (RONO2), and other photochemical products were formed in the atmosphere downwind from the Deepwater Horizon (DWH) oil spill by photochemical reactions of evaporating hydrocarbons with NOx (=NO + NO2) emissions from spill response activities. Reactive nitrogen species and volatile organic compounds (VOCs) were measured from an instrumented aircraft during daytime flights in the marine boundary layer downwind from the area of surfacing oil. A unique VOC mixture, where alkanes dominated the hydroxyl radical (OH) loss rate, was emitted into a clean marine environment, enabling a focused examination of O3 and RONO2 formation processes. In the atmospheric plume from DWH, the OH loss rate, an indicator of potential O3 formation, was large and dominated by alkanes with between 5 and 10 carbons per molecule (C5–C10). Observations showed that NOx was oxidized very rapidly with a 0.8 h lifetime, producing primarily C6–C10 RONO2 that accounted for 78% of the reactive nitrogen enhancements in the atmospheric plume 2.5 h downwind from DWH. Both observations and calculations of RONO2 and O3 production rates show that alkane oxidation dominated O3 formation chemistry in the plume. Rapid and nearly complete oxidation of NOx to RONO2 effectively terminated O3 production, with O3 formation yields of 6.0 ± 0.5 ppbv O3 per ppbv of NOx oxidized. VOC mixing ratios were in large excess of NOx, and additional NOx would have formed additional O3 in this plume. Analysis of measurements of VOCs, O3, and reactive nitrogen species and calculations of O3 and RONO2 production rates demonstrate that NOx‐VOC chemistry in the DWH plume is explained by known mechanisms.
Highlights
[2] Tropospheric ozone (O3) production caused by photochemical reactions between NOx (=NO + NO2) and volatile organic compounds (VOCs) has been studied extensively in urban, industrial, and rural environments [National Research Council Committee on Tropospheric Ozone Formation and Measurement, 1991]
Speciated VOCs and RONO2 were determined by gas chromatography with flame ionization or mass spectrometric analysis of 72 whole air samples collected in stainless steel canisters on each flight [Colman et al, 2001]
Eight RONO2 compounds with between one and five carbon atoms per molecule were measured with Æ10% accuracy, and in a few samples the sum of C6–C8 RONO2 were estimated with approximately Æ50% uncertainty
Summary
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D09305, doi:10.1029/2011JD017150, 2012. Ozone and alkyl nitrate formation from the Deepwater Horizon oil spill atmospheric emissions. [1] Ozone (O3), alkyl nitrates (RONO2), and other photochemical products were formed in the atmosphere downwind from the Deepwater Horizon (DWH) oil spill by photochemical reactions of evaporating hydrocarbons with NOx (=NO + NO2) emissions from spill response activities. Observations showed that NOx was oxidized very rapidly with a 0.8 h lifetime, producing primarily C6–C10 RONO2 that accounted for 78% of the reactive nitrogen enhancements in the atmospheric plume 2.5 h downwind from DWH. Both observations and calculations of RONO2 and O3 production rates show that alkane oxidation dominated O3 formation chemistry in the plume.
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