[1] A comprehensive suite of volatile organic compounds (VOCs) was measured at the semirural Boulder Atmospheric Observatory (BAO) in northeast Colorado during the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign during the winter of 2011. A signature of elevated nonmethane hydrocarbon (NMHC) mixing ratios was observed throughout the campaign. The C 2 -C 5 alkane mixing ratios were an order of magnitude greater than the regional background. Light alkane mixing ratios were similar to those at urban sites impacted by petrochemical industry emissions with ethane and propane reaching maximums of over 100 ppbv. The mean (± standard deviation) calculated total OH reactivity (7.0 ± 5.0 s À1 ) was also similar to urban sites. Analysis of VOC wind direction dependence, emission ratios with tracer compounds, and vertical profiles up to 250 m implicated regional natural gas production activities as the source of the elevated VOCs to the northeast of BAO and urban combustion emissions as the major VOC source to the south of BAO. Elevated acetonitrile and dimethyl sulfide mixing ratios were also associated with natural gas emissions. Fluxes of natural gas associated NMHCs were determined to estimate regional emission rates which ranged from 40 ± 14 Gg yr À1 for propane to 0.03 ± 0.01 Gg yr À1 for n-nonane. These emissions have the potential to impact downwind air quality as natural gas associated NMHCs comprised ≈24% of the calculated OH reactivity. The measurements described here provide a baseline for determining the efficacy of future policies designed to control emissions from natural gas production activities.Citation: Swarthout, R. F., R. S. Russo, Y. Zhou, A. H. Hart, and B. C. Sive (2013), Volatile organic compound distributions during the NACHTT campaign at the Boulder Atmospheric Observatory: Influence of urban and natural gas sources,

[1] Heterogeneous N 2 O 5 uptake onto aerosol is the primary nocturnal path for removal of NO x (= NO + NO 2 ) from the atmosphere and can also result in halogen activation through production of ClNO 2 . The N 2 O 5 uptake coefficient has been the subject of numerous laboratory studies; however, only a few studies have determined the uptake coefficient from ambient measurements, and none has been focused on winter conditions, when the portion of NO x removed by N 2 O 5 uptake is the largest. In this work, N 2 O 5 uptake coefficients are determined from ambient wintertime measurements of N 2 O 5 and related species at the Boulder Atmospheric Observatory in Weld County, CO, a location that is highly impacted by urban pollution from Denver, as well as emissions from agricultural activities and oil and gas extraction. A box model is used to analyze the nocturnal nitrate radical chemistry and predict the N 2 O 5 concentration. The uptake coefficient in the model is iterated until the predicted N 2 O 5 concentration matches the measured concentration. The results suggest that during winter, the most important influence that might suppress N 2 O 5 uptake is aerosol nitrate but that this effect does not suppress uptake coefficients enough to limit the rate of NO x loss through N 2 O 5 hydrolysis. N 2 O 5 hydrolysis was found to dominate the nocturnal chemistry during this study consuming~80% of nocturnal gas phase nitrate radical production. Typically, less than 15% of the total nitrate radical production remained in the form of nocturnal species at sunrise when they are photolyzed and reform NO 2 . , et al. (2013), N 2 O 5 uptake coefficients and nocturnal NO 2 removal rates determined from ambient wintertime measurements, J. Geophys. Res. Atmos., 118,[9331][9332][9333][9334][9335][9336][9337][9338][9339][9340][9341][9342][9343][9344][9345][9346][9347][9348][9349][9350]

[1] Short-lived halocarbon tracers were used to investigate marine influences on air quality in a coastal region of New England. Atmospheric measurements made at the University of New Hampshire's Observing Station at Thompson Farm (TF) in Durham, New Hampshire, indicate that relatively large amounts of halocarbons are emitted from local estuarine and coastal oceanic regions. Bromine-containing halocarbons of interest in this work include bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ). The mean mixing ratios of CHBr 3 and CH 2 Br 2 from 11 January to 5 March 2002 were 2.6 pptv and 1.6 pptv, and from 1 June to 31 August 2002 mean mixing ratios were 5.9 pptv and 1.4 pptv, respectively. The mean mixing ratio of CHBr 3 was not only highest during summer, but both CHBr 3 and CH 2 Br 2 exhibited large variability in their atmospheric mixing ratios during this season. We attribute the greater variability to increased production combined with faster atmospheric removal rates. Other seasonal characteristics of CHBr 3 and CH 2 Br 2 in the atmosphere, as well as the impact of local meteorology on their distributions at this coastal site, are discussed. Tetrachloroethene (C 2 Cl 4 ) and trichloroethene (C 2 HCl 3 ) were used to identify time periods influenced by urban emissions. Additionally, measurements of CHBr 3, CH 2 Br 2, C 2 Cl 4 , methyl iodide (CH 3 I), and ethyl iodide (C 2 H 5 I) were made at TF and five sites throughout the nearby Great Bay estuarine area between 18 and 19 August 2003. These measurements were used to elucidate the effect of the tidal cycle on the distributions of these gases. The mean mixing ratios of CHBr 3 , CH 2 Br 2 , CH 3 I, and C 2 H 5 I were $82%, 46%, 14%, and 17% higher, respectively, near the coast compared to inland sites, providing evidence for a marine source of short-lived halocarbons at TF. Correlation between the tidal cycle and atmospheric concentrations of marine tracers on the night of 18 August 2003 showed that the highest values for the brominated species occurred $2-3 hours after high tide. Emission fluxes of CHBr 3 , CH 2 Br 2 , CH 3 I, and C 2 H 5 I on this night were estimated to be 26 ± 57, 4.7 ± 5.4, 5.9 ± 4.6, and 0.065 ± 0.20 nmol m À2 h À1 , respectively. Finally, the anthropogenic source strength of CHBr 3 was calculated to determine its impact on atmospheric levels observed in this region. Although our results indicate that anthropogenic contributions could potentially range from 15 to 60% of the total dissolved CHBr 3 in the Great Bay, based on the observed ratio of CH 2 Br 2 /CHBr 3 and surface seawater measurements in the Gulf of Maine, it appears unlikely that anthropogenic activities are a significant source of CHBr 3 in the region.

We characterize the chemical composition of Asian continental outflow observed during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) mission during February–April 2001 in the western Pacific using data collected on the NASA DC‐8 aircraft. A significant anthropogenic impact was present in the free troposphere and as far east as 150°E longitude reflecting rapid uplift and transport of continental emissions. Five‐day backward trajectories were utilized to identify five principal Asian source regions of outflow: central, coastal, north‐northwest (NNW), southeast (SE), and west‐southwest (WSW). The maximum mixing ratios for several species, such as CO, C2Cl4, CH3Cl, and hydrocarbons, were more than a factor of 2 larger in the boundary layer of the central and coastal regions due to industrial activity in East Asia. CO was well correlated with C2H2, C2H6, C2Cl4, and CH3Cl at low altitudes in these two regions (r2 ∼ 0.77–0.97). The NNW, WSW, and SE regions were impacted by anthropogenic sources above the boundary layer presumably due to the longer transport distances of air masses to the western Pacific. Frontal and convective lifting of continental emissions was most likely responsible for the high altitude outflow in these three regions. Photochemical processing was influential in each source region resulting in enhanced mixing ratios of O3, PAN, HNO3, H2O2, and CH3OOH. The air masses encountered in all five regions were composed of a complex mixture of photochemically aged air with more recent emissions mixed into the outflow as indicated by enhanced hydrocarbon ratios (C2H2/CO ≥ 3 and C3H8/C2H6 ≥ 0.2). Combustion, industrial activities, and the burning of biofuels and biomass all contributed to the chemical composition of air masses from each source region as demonstrated by the use of C2H2, C2Cl4, and CH3Cl as atmospheric tracers. Mixing ratios of O3, CO, C2H2, C2H6, SO2, and C2Cl4 were compared for the TRACE‐P and PEM‐West B missions. In the more northern regions, O3, CO, and SO2 were higher at low altitudes during TRACE‐P. In general, mixing ratios were fairly similar between the two missions in the southern regions. A comparison between CO/CO2, CO/CH4, C2H6/C3H8, NOx/SO2, and NOy/(SO2 + nss‐SO4) ratios for the five source regions and for the 2000 Asian emissions summary showed very close agreement indicating that Asian emissions were well represented by the TRACE‐P data and the emissions inventory.

The Marcellus Shale is the largest natural gas deposit in the U.S. and rapid development of this resource has raised concerns about regional air pollution. A field campaign was conducted in the southwestern Pennsylvania region of the Marcellus Shale to investigate the impact of unconventional natural gas (UNG) production operations on regional air quality. Whole air samples were collected throughout an 8050 km(2) grid surrounding Pittsburgh and analyzed for methane, carbon dioxide, and C1-C10 volatile organic compounds (VOCs). Elevated mixing ratios of methane and C2-C8 alkanes were observed in areas with the highest density of UNG wells. Source apportionment was used to identify characteristic emission ratios for UNG sources, and results indicated that UNG emissions were responsible for the majority of mixing ratios of C2-C8 alkanes, but accounted for a small proportion of alkene and aromatic compounds. The VOC emissions from UNG operations accounted for 17 ± 19% of the regional kinetic hydroxyl radical reactivity of nonbiogenic VOCs suggesting that natural gas emissions may affect compliance with federal ozone standards. A first approximation of methane emissions from the study area of 10.0 ± 5.2 kg s(-1) provides a baseline for determining the efficacy of regulatory emission control efforts.