Natural gas production is associated with emissions of several trace gases, some of them classified as air toxics. While volatile organic compounds (VOCs) have received much attention, hydrogen ...sulfide (H2S) can also be of concern due to the known health impacts of exposure to this hazardous air pollutant. Here, we present quantitative, fast time-response measurements of H2S using proton-transfer-reaction mass-spectrometry (PTR-MS) instruments. An ultra-light-weight PTR-MS (ULW-PTR-MS) in a mobile laboratory was operated for measurements of VOCs and H2S in a gas and oil field during the Uintah Basin Winter Ozone Study (UBWOS) 2012 campaign. Measurements of VOCs and H2S by a PTR-MS were also made at the Horse Pool ground site in the Uintah Basin during UBWOS 2013. The H2S measurement by PTR-MS is strongly humidity dependent because the proton affinity of H2S is only slightly higher than that of water. The H2S sensitivity of PTR-MS ranged between 0.6-1.4 ncps ppbv-1 during UBWOS 2013. We compare the humidity dependence determined in the laboratory with in-field calibrations and determine the H2S mixing ratios for the mobile and ground measurements. The PTR-MS measurements at Horse Pool are evaluated by comparison with simultaneous H2S measurements using a PTR time-of-flight MS (PTR-ToF-MS) and a Picarro cavity ring down spectroscopy (CRDS) instrument for H2S / CH4. On average 0.6 plus or minus 0.3 ppbv H2S was present at Horse Pool during UBWOS 2013. The correlation between H2S and methane enhancements suggests that the source of H2S is associated with oil and gas extraction in the basin. Significant H2S mixing ratios of up to 9 ppmv downwind of storage tanks were observed during the mobile measurements. This study suggests that H2S emissions associated with oil and gas production can lead to short-term high levels close to point sources, and elevated background levels away from those sources. In addition, our work has demonstrated that PTR-MS can make reliable measurements of H2S at levels below 1 ppbv.
Severe type I plasminogen (PLG) deficiency has been causally linked to a rare chronic inflammatory disease of the mucous membranes that may be life threatening. Here we report clinical ...manifestations, PLG plasma levels, and molecular genetic status of the PLG gene of 50 patients. The most common clinical manifestations among these patients were ligneous conjunctivitis (80%) and ligneous gingivitis (34%), followed by less common manifestations such as ligneous vaginitis (8%), and involvement of the respiratory tract (16%), the ears (14%), or the gastrointestinal tract (2%). Four patients showed congenital occlusive hydrocephalus, 2 with Dandy-Walker malformation of cerebellum. Venous thrombosis was not observed. In all patients, plasma PLG levels were markedly reduced. In 38 patients, distinct mutations in the PLG gene were identified. The most common genetic alteration was a K19E mutation found in 34% of patients. Transient in vitro expression of PLG mutants R134K, delK212, R216H, P285T, P285A, T319_N320insN, and R776H in transfected COS-7 cells revealed significantly impaired secretion and increased degradation of PLG. These results demonstrate impaired secretion of mutant PLG proteins as a common molecular pathomechanism in type I PLG deficiency.
Aerosol indirect radiative forcing (IRF), which characterizes how aerosols alter cloud formation and properties, is very sensitive to the preindustrial (PI) aerosol burden. Dimethyl sulfide (DMS), ...emitted from the ocean, is a dominant natural precursor of non-sea-salt sulfate in the PI and pristine present-day (PD) atmospheres. Here we revisit the atmospheric oxidation chemistry of DMS, particularly under pristine conditions, and its impact on aerosol IRF. Based on previous laboratory studies, we expand the simplified DMS oxidation scheme used in the Community Atmospheric Model version 6 with chemistry (CAM6-chem) to capture the OH-addition pathway and the H-abstraction pathway and the associated isomerization branch. These additional oxidation channels of DMS produce several stable intermediate compounds, e.g., methanesulfonic acid (MSA) and hydroperoxymethyl thioformate (HPMTF), delay the formation of sulfate, and,
hence, alter the spatial distribution of sulfate aerosol and radiative
impacts. The expanded scheme improves the agreement between modeled and
observed concentrations of DMS, MSA, HPMTF, and sulfate over most marine
regions, based on the NASA Atmospheric Tomography (ATom), the Aerosol and
Cloud Experiments in the Eastern North Atlantic (ACE-ENA), and the
Variability of the American Monsoon Systems (VAMOS)
Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx)
measurements. We find that the global HPMTF burden and the burden of sulfate produced from DMS oxidation are relatively insensitive to the
assumed isomerization rate, but the burden of HPMTF is very sensitive to a
potential additional cloud loss. We find that global sulfate burden under PI and PD emissions increase to 412 Gg S (+29 %) and 582 Gg S (+8.8 %), respectively, compared to the standard simplified DMS oxidation scheme. The resulting annual mean global PD direct radiative effect of DMS-derived sulfate alone is −0.11 W m−2. The enhanced PI sulfate produced via the gas-phase chemistry updates alone dampens the aerosol IRF as anticipated (−2.2 W m−2 in standard versus −1.7 W m−2, with updated gas-phase chemistry). However, high clouds in the tropics and low clouds in the Southern Ocean appear particularly sensitive to the additional aqueous-phase pathways, counteracting this change (−2.3 W m−2). This study confirms
the sensitivity of aerosol IRF to the PI aerosol loading and the
need to better understand the processes controlling aerosol formation in the PI atmosphere and the cloud response to these changes.
We analyze an expanded data set of oxygenated volatile organic compounds (OVOCs) in air measured by several instruments at a surface site in Pasadena near Los Angeles during the National Oceanic and ...Atmospheric Administration California Nexus study in 2010. The contributions of emissions, chemical formation, and removal are quantified for each OVOC using CO as a tracer of emissions and the OH exposure of the sampled air masses calculated from hydrocarbon ratios. The method for separating emissions from chemical formation is evaluated using output for Pasadena from the Weather Research and Forecasting‐Chemistry model. The model is analyzed by the same method as the measurement data, and the emission ratios versus CO calculated from the model output agree for ketones with the inventory used in the model but overestimate aldehydes by ~70%. In contrast with the measurements, nighttime formation of OVOCs is significant in the model and is attributed to overestimated precursor emissions and overestimated rate coefficients for the reactions of the precursors with ozone and NO3. Most measured aldehydes correlated strongly with CO at night, suggesting a contribution from motor vehicle emissions. However, the emission ratios of most aldehydes versus CO are higher than those reported in motor vehicle emissions and the aldehyde sources remain unclear. Formation of several OVOCs is investigated in terms of the removal of specific precursors. Direct emissions of alcohols and aldehydes contribute significantly to OH reactivity throughout the day, and these emissions should be accurately represented in models describing ozone formation.
Plain Language Summary
We report new measurements of volatile organic compounds (VOCs) in ambient air in the Los Angeles basin. Chemical reactions between VOCs and nitrogen oxides form ozone and fine particles, two important pollutants in Los Angeles smog. It is therefore important to understand VOC emission sources. In this work, we derive the composition of VOC emissions using ambient measurements at Pasadena in 2010. The study is complicated due to rapid chemical reactions that can form and remove VOCs in between the time of emission and measurement. After correcting for this chemistry, it is shown that emissions of many oxygen‐containing VOCs are important for the formation of ozone.
Key Points
An extensive and expanded data set of oxygenated VOCs in ambient air in the Los Angeles basin is analyzed
The composition of directly emitted oxygenated VOCs is determined after accounting for the effects of their chemical formation and removal
Aldehydes are important for urban photochemistry, but their sources remain poorly understood
Formaldehyde (HCHO) is one of the most abundant non-methane volatile organic compounds (VOCs) emitted by fires. HCHO also undergoes chemical
production and loss as a fire plume ages, and it can be an ...important oxidant precursor. In this study, we disentangle the processes controlling HCHO
by examining its evolution in wildfire plumes sampled by the NASA DC-8 during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ) field campaign. In 9 of the 12 analyzed plumes,
dilution-normalized HCHO increases with physical age (range 1–6 h). The balance of HCHO loss (mainly via photolysis) and production (via
OH-initiated VOC oxidation) seems to control the sign and magnitude of this trend. Plume-average OH concentrations, calculated from VOC decays,
range from −0.5 (± 0.5) × 106 to 5.3 (± 0.7) × 106 cm−3. The production and loss rates of
dilution-normalized HCHO seem to decrease with plume age. Plume-to-plume variability in dilution-normalized secondary HCHO production correlates
with OH abundance rather than normalized OH reactivity, suggesting that OH is the main driver of fire-to-fire variability in HCHO secondary
production. Analysis suggests an effective HCHO yield of 0.33 (± 0.05) per VOC molecule oxidized for the 12 wildfire plumes. This finding can
help connect space-based HCHO observations to the oxidizing capacity of the atmosphere and to VOC emissions.
Total OH reactivity was measured during the California Research at the Nexus of Air Quality and Climate Change field campaign at the Pasadena ground site using a turbulent flow tube reactor with ...laser‐induced fluorescence detection of the OH radical. Collocated measurements of volatile organic compounds (VOCs), inorganic species, and meteorological parameters were made and used to calculate the total OH reactivity, which was then compared to the measured values. An analysis of the OH reactivity measurements finds that although the measured reactivity correlated well with the calculated reactivity, the measurements were consistently greater than the calculations for all times during the day, with an average missing OH reactivity of 8–10 s−1, accounting for approximately 40% of the measured total OH reactivity. An analysis of correlations with both anthropogenic tracers of combustion and oxygenated VOCs as well as air trajectories during the campaign suggest that the missing OH reactivity was likely due to a combination of both unmeasured local emissions and unmeasured oxidation products transported to the site. Approximately 50% of the missing OH reactivity may have been due to emissions of unmeasured volatile chemical products, such as pesticides, cleaning agents, and personal care products.
Key Points
Total OH reactivity measured during the CalNex‐LA field campaign was consistently greater than that calculated from measured OH sinks
An analysis suggests that the missing reactivity is likely due to both unmeasured local emissions and unmeasured oxidation products
Approximately 50% of the missing OH reactivity may have been due to emissions of unmeasured volatile chemical products
Earth's atmosphere oxidizes the greenhouse gas methane and other gases, thus determining their lifetimes and oxidation products. Much of this oxidation occurs in the remote, relatively clean free ...troposphere above the planetary boundary layer, where the oxidation chemistry is thought to be much simpler and better understood than it is in urban regions or forests. The NASA airborne Atmospheric Tomography study (ATom) was designed to produce cross sections of the detailed atmospheric composition in the remote atmosphere over the Pacific and Atlantic Oceans during four seasons. As part of the extensive ATom data set, measurements of the atmosphere's primary oxidant, hydroxyl (OH), and hydroperoxyl (HO2) are compared to a photochemical box model to test the oxidation chemistry. Generally, observed and modeled median OH and HO2 agree to within combined uncertainties at the 2σ confidence level, which is ~±40%. For some seasons, this agreement is within ~±20% below 6-km altitude. While this test finds no significant differences, OH observations increasingly exceeded modeled values at altitudes above 8 km, becoming ~35% greater, which is near the combined uncertainties. Measurement uncertainty and possible unknown measurement errors complicate tests for unknown chemistry or incorrect reaction rate coefficients that would substantially affect the OH and HO2 abundances. Future analysis of detailed comparisons may yield additional discrepancies that are masked in the median values.
Ethanol made from corn now constitutes approximately 10% of the fuel used in gasoline vehicles in the U.S. The ethanol is produced in over 200 fuel ethanol refineries across the nation. We report ...airborne measurements downwind from Decatur, Illinois, where the third largest fuel ethanol refinery in the U.S. is located. Estimated emissions are compared with the total point source emissions in Decatur according to the 2011 National Emissions Inventory (NEI‐2011), in which the fuel ethanol refinery represents 68.0% of sulfur dioxide (SO2), 50.5% of nitrogen oxides (NOx = NO + NO2), 67.2% of volatile organic compounds (VOCs), and 95.9% of ethanol emissions. Emissions of SO2 and NOx from Decatur agreed with NEI‐2011, but emissions of several VOCs were underestimated by factors of 5 (total VOCs) to 30 (ethanol). By combining the NEI‐2011 with fuel ethanol production numbers from the Renewable Fuels Association, we calculate emission intensities, defined as the emissions per ethanol mass produced. Emission intensities of SO2 and NOx are higher for plants that use coal as an energy source, including the refinery in Decatur. By comparing with fuel‐based emission factors, we find that fuel ethanol refineries have lower NOx, similar VOC, and higher SO2 emissions than from the use of this fuel in vehicles. The VOC emissions from refining could be higher than from vehicles, if the underestimated emissions in NEI‐2011 downwind from Decatur extend to other fuel ethanol refineries. Finally, chemical transformations of the emissions from Decatur were observed, including formation of new particles, nitric acid, peroxyacyl nitrates, aldehydes, ozone, and sulfate aerosol.
Key Points
Emissions from the third largest fuel ethanol refinery in the U.S. were measured
Emissions of NOx and SO2 agreed with the NEI‐2011 emission inventory
Emissions of VOCs were underestimated by the NEI‐2011 inventory
The nocturnal conversion of dinitrogen pentoxide (N2O5) to nitryl chloride (ClNO2) on chloride‐containing aerosol can be a regionally important NOx (= NO + NO2) recycling and halogen activation ...pathway that affects oxidant photochemistry the following day. Here we present a comprehensive measurement data set acquired at Pasadena, California, during the CalNex‐LA campaign 2010 that included measurements of odd nitrogen and its major components (NOy = NOx + NO3 + 2N2O5 + ClNO2 + HNO3 + HONO + peroxyacyl, alkyl, and aerosol nitrates) and aerosol size distribution and composition. Nitryl chloride was present during every night of the study (median mixing ratio at sunrise 800 pptv) and was usually a more significant nocturnal NOx and odd oxygen (Ox = O3 + NO2 + 3N2O5 + ClNO2) reservoir species than N2O5 (whose concentrations were calculated from its equilibrium with NO2 and NO3). At sunrise, ClNO2 accounted for 21% of NOz (=NOy − NOx), 4% of NOy, and 2.5% of Ox, respectively (median values). Kinetic parameters for the N2O5 to ClNO2 conversion were estimated by relating ClNO2 concentrations to their time‐integrated heterogeneous production from N2O5 and were highly variable between nights. Production of ClNO2 required conversion of N2O5 on submicron aerosol with average yield (φ) and N2O5 reactive uptake probability (γ) of γφ = 0.008 (maximum 0.04), scaled with submicron aerosol chloride content, and was suppressed by aerosol organic matter and liquid water content. Not all of the observed variability of ClNO2 production efficiency could be rationalized using current literature parameterizations.
Key Points
We present field measurements of ClNO2 during Calnex‐LA 2010.ClNO2 was a more significant nocturnal NOx and Ox reservoir than N2O5.Rates of N2O5 to ClNO2 conversion varied between nights.
Bromine activation (the production of Br in an elevated oxidation state) promotes ozone destruction and mercury removal in the global troposphere and commonly occurs in both springtime polar boundary ...layers, often accompanied by nearly complete ozone destruction. The chemistry and budget of active bromine compounds (e.g., Br2, BrCl, BrO, HOBr) reflect the cycling of Br and affect its environmental impact. Cyanogen bromide (BrCN) has recently been measured by iodide ion high-resolution time-of-flight mass spectrometry (I- CIMS), and trifluoro methoxide ion time-of-flight mass spectrometry (CF3O- CIMS) during the NASA Atmospheric Tomography Mission second, third, and fourth deployments (NASA ATom), and could be a previously unquantified participant in active Br chemistry. BrCN mixing ratios ranged from below the detection limit (1.5 pptv) up to as high as 36 pptv (10 s average) and enhancements were almost exclusively confined to the polar boundary layers in the Arctic winter and in both polar regions during spring and fall. The coincidence of BrCN with active Br chemistry (often observable BrO, BrCl and O3 loss) and high CHBr3/CH2Br2 ratios imply that much of the observed BrCN is from atmospheric Br chemistry rather than a biogenic source. Likely BrCN formation pathways involve the heterogeneous reactions of active Br (Br2, HOBr) with reduced nitrogen compounds, for example hydrogen cyanide (HCN/CN-), on snow, ice, or particle surfaces. Competitive reaction calculations of HOBr reactions with Cl-/Br- and HCN/CN- in solution, as well as box model calculations with bromine chemistry, confirm the viability of this formation channel and show a distinct pH dependence, with BrCN formation favored at higher pH values. Gas-phase loss processes of BrCN due to reaction with radical species are likely quite slow and photolysis is known to be relatively slow (BrCN lifetime of ∼ 4 months in midlatitude summer). These features, and the lack of BrCN enhancements above the polar boundary layer, imply that surface reactions must be the major loss processes. The fate of BrCN determines whether BrCN production fuels or terminates bromine activation. BrCN reactions with other halogens (Br-, HOCl, HOBr) may perpetuate the active Br cycle; however, preliminary laboratory experiments showed that BrCN did not react with aqueous bromide ion (< 0.1 %) to reform Br2. Liquid-phase reactions of BrCN are more likely to convert Br to bromide (Br-) or form a C–Br bonded organic species, as these are the known condensed-phase reactions of BrCN and would therefore constitute a loss of atmospheric active Br. Thus, further study of the chemistry of BrCN will be important for diagnosing polar Br cycling.
PDF
