Bromine measurements in ozone depleted air over the Arctic Ocean

In situ measurements of ozone, photochemically active bromine compounds, and other trace gases over the Arctic Ocean in April 2008 are used to examine the chemistry and geographical extent of ozone depletion in the arctic marine boundary layer (MBL). Data were obtained from the NOAA WP-3D aircraft during the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study and the NASA DC-8 aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) study. Fast (1 s) and sensitive (detection limits at the low pptv level) measurements of BrCl and BrO were obtained from three different chemical ionization mass spectrometer (CIMS) instruments, and soluble bromide was measured with a mist chamber. The CIMS instruments also detected Br2. Subsequent laboratory studies showed that HOBr rapidly converts to Br2 on the Teflon instrument inlets. This detected Br2 is identified as active bromine and represents a lower limit of the sum HOBr + Br2. The measured active bromine is shown to likely be HOBr during daytime flights in the arctic. In the MBL over the Arctic Ocean, soluble bromide and active bromine were consistently elevated and ozone was depleted. Ozone depletion and active bromine enhancement were confined to the MBL that was capped by a temperature inversion at 200–500 m altitude. In ozone-depleted air, BrO rarely exceeded 10 pptv and was always substantially lower than soluble bromide that was as high as 40 pptv. BrCl was rarely enhanced above the 2 pptv detection limit, either in the MBL, over Alaska, or in the arctic free troposphere

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

Widespread efforts to abate ozone (O3) smog have significantly reduced emissions of nitrogen oxides (NOx) over the past 2 decades in the Southeast US, a place heavily influenced by both anthropogenic and biogenic emissions. How reactive nitrogen speciation responds to the reduction in NOx emissions in this region remains to be elucidated. Here we exploit aircraft measurements from ICARTT (July–August 2004), SENEX (June–July 2013), and SEAC4RS (August–September 2013) and long-term ground measurement networks alongside a global chemistry–climate model to examine decadal changes in summertime reactive oxidized nitrogen (RON) and ozone over the Southeast US. We show that our model can reproduce the mean vertical profiles of major RON species and the total (NOy) in both 2004 and 2013. Among the major RON species, nitric acid (HNO3) is dominant (∼ 42–45%), followed by NOx (31%), total peroxy nitrates (ΣPNs; 14%), and total alkyl nitrates (ΣANs; 9–12%) on a regional scale. We find that most RON species, including NOx, ΣPNs, and HNO3, decline proportionally with decreasing NOx emissions in this region, leading to a similar decline in NOy. This linear response might be in part due to the nearly constant summertime supply of biogenic VOC emissions in this region. Our model captures the observed relative change in RON and surface ozone from 2004 to 2013. Model sensitivity tests indicate that further reductions of NOxemissions will lead to a continued decline in surface ozone and less frequent high-ozone events

Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift

Ethane is the second most abundant atmospheric hydrocarbon, exerts a strong influence on tropospheric ozone, and reduces the atmosphere’s oxidative capacity. Global observations showed declining ethane abundances from 1984 to 2010, while a regional measurement indicated increasing levels since 2009, with the reason for this subject to speculation. The Bakken shale is an oil and gas‐producing formation centered in North Dakota that experienced a rapid increase in production beginning in 2010. We use airborne data collected over the North Dakota portion of the Bakken shale in 2014 to calculate ethane emissions of 0.23 ± 0.07 (2σ) Tg/yr, equivalent to 1–3% of total global sources. Emissions of this magnitude impact air quality via concurrent increases in tropospheric ozone. This recently developed large ethane source from one location illustrates the key role of shale oil and gas production in rising global ethane levels.Key PointsThe Bakken shale in North Dakota accounted for 1–3% total global ethane emissions in 2014These findings highlight the importance of shale production in global atmospheric ethane shiftThese emissions impact air quality and influence interpretations of recent global methane changesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142509/1/grl54333.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142509/2/grl54333-sup-0001-2016GL068703-SI.pd

Methyl, ethyl, and propyl nitrates: global distribution and impacts on reactive nitrogen in remote marine environments

Alkyl nitrates (RONO2) are important components of tropospheric reactive nitrogen that serve as reservoirs for nitrogen oxides (NOx ≡ NO + NO2). Here we implement a new simulation of atmospheric methyl, ethyl, and propyl nitrate chemistry in a global chemical transport model (GEOS‐Chem). We show that the model can reproduce the spatial and seasonal variability seen in a 20‐year ensemble of airborne observations. Methyl nitrate accounts for 17 Gg N globally, with maxima over the tropical Pacific and Southern Ocean. Propyl nitrate is enhanced in continental boundary layers, but its global impact (6 Gg N) is limited by a short lifetime (8 days, versus 26 days for methyl nitrate and 14 days for ethyl nitrate) that inhibits long‐range transport. Ethyl nitrate has the smallest impact of the three species (4 Gg N). We find that methyl nitrate is the dominant form of reactive nitrogen (NOy) in the Southern Ocean marine boundary layer, where its addition to the model corrects a large NOy underestimate in austral winter relative to recent aircraft data. RONO2 serve as a small net NOx source to the marine troposphere, except in the northern mid‐latitudes where the continental outflow is enriched in precursors that promote NOx loss via RONO2 formation. Recent growth in NOx emissions from East Asia has enhanced the role of RONO2 as a source of NOx to the remote free troposphere. This relationship implies projected future NOx emissions growth across the southern hemisphere may further enhance the importance of RONO2 as a NOx reservoir

Quantifying atmospheric methane emissions from oil and natural gas production in the Bakken shale region of North Dakota

We present in situ airborne measurements of methane (CH4) and ethane (C2H6) taken aboard a NOAA DHC‐6 Twin Otter research aircraft in May 2014 over the Williston Basin in northwestern North Dakota, a region of rapidly growing oil and natural gas production. The Williston Basin is best known for the Bakken shale formation, from which a significant increase in oil and gas extraction has occurred since 2009. We derive a CH4 emission rate from this region using airborne data by calculating the CH4 enhancement flux through the planetary boundary layer downwind of the region. We calculate CH4 emissions of (36 ± 13), (27 ± 13), (27 ± 12), (27 ± 12), and (25 ± 10) × 103 kg/h from five transects on 3 days in May 2014 downwind of the Bakken shale region of North Dakota. The average emission, (28 ± 5) × 103 kg/h, extrapolates to 0.25 ± 0.05 Tg/yr, which is significantly lower than a previous estimate of CH4 emissions from northwestern North Dakota and southeastern Saskatchewan using satellite remote sensing data. We attribute the majority of CH4 emissions in the region to oil and gas operations in the Bakken based on the similarity between atmospheric C2H6 to CH4 enhancement ratios and the composition of raw natural gas withdrawn from the region.Key PointsCH4 emissions from the Bakken region of North Dakota quantifiedFirst emission estimate using in situ CH4 measurementsCH4 sources dominated by oil‐ and gas‐related activitiesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122415/1/jgrd52986.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122415/2/jgrd52986_am.pd