Carbonyl sulfide (OCS) and carbon disulfide (CS2) are
volatile sulfur gases that are naturally formed in seawater and exchanged
with the atmosphere. OCS is the most abundant sulfur gas in the ...atmosphere,
and CS2 is its most important precursor. They have attracted increased interest due
to their direct (OCS) or indirect (CS2 via oxidation to OCS)
contribution to the stratospheric sulfate aerosol layer. Furthermore, OCS
serves as a proxy to constrain terrestrial CO2 uptake by vegetation.
Oceanic emissions of both gases contribute a major part to their atmospheric
concentration. Here we present a database of previously published and
unpublished (mainly shipborne) measurements in seawater and the marine
boundary layer for both gases, available at https://doi.org/10.1594/PANGAEA.905430 (Lennartz et
al., 2019). The database contains original measurements as well as data
digitalized from figures in publications from 42 measurement campaigns, i.e.,
cruises or time series stations, ranging from 1982 to 2019. OCS data cover
all ocean basins except for the Arctic Ocean, as well as all months of the
year, while the CS2 dataset shows large gaps in spatial and temporal
coverage. Concentrations are consistent across different sampling and
analysis techniques for OCS. The database is intended to support the
identification of global spatial and temporal patterns and to facilitate the
evaluation of model simulations.
During the Deepwater Horizon (DWH) oil spill, a wide range of gas and aerosol species were measured from an aircraft around, downwind, and away from the DWH site. Additional hydrocarbon measurements ...were made from ships in the vicinity. Aerosol particles of respirable sizes were on occasions a significant air quality issue for populated areas along the Gulf Coast. Yields of organic aerosol particles and emission factors for other atmospheric pollutants were derived for the sources from the spill, recovery, and cleanup efforts. Evaporation and subsequent secondary chemistry produced organic particulate matter with a mass yield of 8 ± 4% of the oil mixture reaching the water surface. Approximately 4% by mass of oil burned on the surface was emitted as soot particles. These yields can be used to estimate the effects on air quality for similar events as well as for this spill at other times without these data. Whereas emission of soot from burning surface oil was large during the episodic burns, the mass flux of secondary organic aerosol to the atmosphere was substantially larger overall. We use a regional air quality model to show that some observed enhancements in organic aerosol concentration along the Gulf Coast were likely due to the DWH spill. In the presence of evaporating hydrocarbons from the oil, NO ₓ emissions from the recovery and cleanup operations produced ozone.
The Stratosphere–Troposphere Analyses of Regional Transport 2008 (START08) experiment investigated a number of important processes in the extratropical upper troposphere and lower stratosphere (UTLS) ...using the National Science Foundation (NSF)–NCAR Gulfstream V (GV) research aircraft. The main objective was to examine the chemical structure of the extratropical UTLS in relation to dynamical processes spanning a range of scales. The campaign was conducted during April–June 2008 from Broomfield, Colorado. A total of 18 research flights sampled an extensive geographical region of North America (25°–65°N, 80°–120°W) and a wide range of meteorological conditions. The airborne in situ instruments measured a comprehensive suite of chemical constituents and microphysical variables from the boundary layer to the lower stratosphere, with flights specifically designed to target key transport processes in the extratropical UTLS. The flights successfully investigated stratosphere–troposphere exchange (STE) processes, including the intrusion of tropospheric air into the stratosphere in association with the secondary tropopause and the intrusion of stratospheric air deep into the troposphere. The flights also sampled the influence of convective transport and lightning on the upper troposphere as well as the distribution of gravity waves associated with multiple sources, including fronts and topography. The aircraft observations are complemented by satellite observations and modeling. The measurements will be used to improve the representation of UTLS chemical gradients and transport in Chemistry–Climate models (CCMs). This article provides an overview of the experiment design and selected observational highlights.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300-700 hPa). Here, using data collected during aircraft ...sampling of the TWP in winter 2014, we find strong, positive correlations of O3 with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O3 and that low H2O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.
Intrusions of air from the tropical upper troposphere into the extratropical stratosphere above the subtropical jet potentially have a significant impact on the composition of the lowermost ...stratosphere (the stratospheric part of the “middle world”). We present an analysis of tropospheric intrusion events observed during the Stratosphere‐Troposphere Analyses of Regional Transport 2008 (START08) experiment using kinematic and chemical diagnostics. The transport processes operating during each event are discussed using high‐resolution model analyses and backward trajectory calculations. Each intrusion observed during START08 can be related to a Rossby wavebreaking event over the Pacific Ocean. Trajectory analysis shows that the intruding air masses can be traced back to the tropical upper troposphere and lower stratosphere. In situ chemical observations of the tropospheric intrusions are used to estimate the mixing time scales of the observed intrusions through use of a simple box model and trace species with different photochemical lifetimes. We estimate that the time scale for an intrusion to mix with the background stratospheric air is 5 to 6 days. Detailed analysis of small‐scale features with tropospheric characteristics observed in the stratosphere suggests frequent irreversible transport associated with tropospheric intrusions. Trace gas distributions and correlations are consistent with the dynamics of the high‐resolution NCEP GFS analyses, suggesting that these features are captured by the GFS assimilation and forecast system. A global analysis of intrusion events observed during the START08 time period (April–June 2008) is also given.
This paper presents determinations of reactive uptake coefficients for N2O5, γ(N2O5), on aerosols from nighttime aircraft measurements of ozone, nitrogen oxides, and aerosol surface area on the NOAA ...P‐3 during Second Texas Air Quality Study (TexAQS II). Determinations based on both the steady state approximation for NO3 and N2O5 and a plume modeling approach yielded γ(N2O5) substantially smaller than current parameterizations used for atmospheric modeling and generally in the range 0.5–6 × 10−3. Dependence of γ(N2O5) on variables such as relative humidity and aerosol composition was not apparent in the determinations, although there was considerable scatter in the data. Determinations were also inconsistent with current parameterizations of the rate coefficient for homogenous hydrolysis of N2O5 by water vapor, which may be as much as a factor of 10 too large. Nocturnal halogen activation via conversion of N2O5 to ClNO2 on chloride aerosol was not determinable from these data, although limits based on laboratory parameterizations and maximum nonrefractory aerosol chloride content showed that this chemistry could have been comparable to direct production of HNO3 in some cases.
We infer surface fluxes of bromoform (CHBr3) and
dibromoform (CH2Br2) from aircraft observations over the western
Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric
chemistry ...model and a maximum a posteriori inverse model. Using GEOS-Chem (GC) as
an intermediary, we find that the distribution of a priori ocean
emissions of these gases are reasonably consistent with observed atmospheric
mole fractions of CHBr3 (r=0.62) and CH2Br2
(r=0.38). These a priori emissions result in a positive model bias
in CHBr3 peaking in the marine boundary layer, but reproduce
observed values of CH2Br2 with no significant bias by virtue of
its longer atmospheric lifetime. Using GEOS-Chem, we find that observed
variations in atmospheric CHBr3 are determined equally by sources
over the western Pacific and those outside the study region, but observed
variations in CH2Br2 are determined mainly by sources outside
the western Pacific. Numerical closed-loop experiments show that the spatial
and temporal distribution of boundary layer aircraft data have the potential
to substantially improve current knowledge of these fluxes, with improvements
related to data density. Using the aircraft data, we estimate aggregated
regional fluxes of 3.6±0.3×108 and 0.7±0.1×108 g month−1 for CHBr3 and CH2Br2 over
130–155∘E and 0–12∘ N, respectively, which represent
reductions of 20 %–40 % of the prior inventories by Ordóñez
et al. (2012) and substantial spatial deviations from different a
priori inventories. We find no evidence to support a robust linear
relationship between CHBr3 and CH2Br2 oceanic
emissions, as used by previous studies. We find that over regions with dense
observation coverage, our choice of a priori inventory does not
significantly impact our reported a posteriori flux estimates.
A chemical ionization mass spectrometer was used to measure BrO and HOBr+Br2 over the Tropical West Pacific Ocean within the altitude range of 1 to 15km, during the CONvective TRansport of Active ...Species in the Tropics (CONTRAST) campaign in 2014. Isolated episodes of elevated BrO (up to 6.6pptv) and/or HOBr+Br2 (up to 7.3pptv) were observed in the tropical free troposphere (TFT) and were associated with biomass burning. However, most of the time we did not observe significant BrO or HOBr+Br2 in the TFT and the tropical tropopause layer (TTL) above our limits of detection (LOD). The 1min average LOD for BrO ranged from 0.6 to 1.6pptv and for HOBr+Br2 ranged from 1.3 to 3.5pptv. During one flight, BrO observations from the TTL to the extratropical lowermost stratosphere were used to infer a profile of inorganic bromine (Bry). Based on this profile, we estimated the product gas injection of bromine species into the stratosphere to be 2pptv. Analysis of Bry partitioning further indicates that BrO levels are likely very low in the TFT environment and that future studies should target the measurement of HBr or atomic Br. Key Points BrO observations throughout the tropics from 1 to 15km were typically below a limit of detection of 1pptv and were compatible with zero BrO and HOBr were observed at significant levels in biomass burning plumes in the tropical free troposphere Model calculations indicate that BrO is a minor constituent of Bry in the tropics and highlight the importance of measuring HBr in the future
The stratospheric inorganic bromine (Bry) burden arising from the degradation of brominated very short-lived organic substances (VSLorg) and its partitioning between reactive and reservoir species is ...needed for a comprehensive assessment of the ozone depletion potential of brominated trace gases. Here we present modeled inorganic bromine abundances over the Pacific tropical tropopause based on aircraft observations of VSLorg from two campaigns of the Airborne Tropical TRopopause EXperiment (ATTREX 2013, carried out over the eastern Pacific, and ATTREX 2014, carried out over the western Pacific) and chemistry-climate simulations (along ATTREX flight tracks) using the specific meteorology prevailing. Using the Community Atmosphere Model with Chemistry (CAM-Chem) we model that BrO and Br are the daytime dominant species. Integrated across all ATTREX flights, BrO represents ∼ 43 and 48 % of daytime Bry abundance at 17 km over the western and eastern Pacific, respectively. The results also show zones where Br / BrO > 1 depending on the solar zenith angle (SZA), ozone concentration, and temperature. On the other hand, BrCl and BrONO2 were found to be the dominant nighttime species with ∼ 61 and 56 % of abundance at 17 km over the western and eastern Pacific, respectively. The western-to-eastern differences in the partitioning of inorganic bromine are explained by different abundances of ozone (O3), nitrogen dioxide (NO2), total inorganic chlorine (Cly), and the efficiency of heterogeneous reactions of bromine reservoirs (mostly BrONO2 and HBr) occurring on ice crystals.
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 vs. 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 midlatitudes 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.
Plain Language Summary
Nitrogen in the atmosphere has many impacts on atmospheric chemistry, including affecting how polluted the air is. Many nitrogen‐containing gases are released over polluted areas and are quickly broken down—staying far away from remote areas like the ocean. In this paper, we investigate a group of nitrogen gases (called alkyl nitrates) that break down more slowly and so stay in the atmosphere long enough to be transported to the otherwise pollution‐free remote Pacific Ocean. These gases are also created naturally in the ocean and then make their way into the atmosphere, changing the atmospheric chemistry over the ocean. We use 20 years of measurements collected from aircraft, combined with a computer model, to determine the abundance and impacts of alkyl nitrates. We find that the smallest alkyl nitrates are particularly important over the Southern Ocean, where there are few other sources of nitrogen. We show that alkyl nitrates are playing an increasingly important role over the remote oceans because of recent growth in East Asian air pollution. This relationship implies that these gases may have a stronger influence on atmospheric chemistry over remote ocean areas in future if anticipated pollution growth in Africa, South America, and Southeast Asia is realised.
Key Points
Model including air‐sea exchange reproduces observed alkyl nitrates from 20 years of airborne data
Methyl nitrate is the dominant form of reactive nitrogen in the tropical Pacific and Southern Ocean
Alkyl nitrates serve as a small but growing source of nitrogen oxides to the remote troposphere
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