We present an estimation of the uptake coefficient (γ) and yield of nitryl chloride (ClNO2) (f) for the heterogeneous processing of dinitrogen pentoxide (N2O5) using simultaneous measurements of ...particle and trace gas composition at a semi-rural, non-coastal, mountain site in the summer of 2011. The yield of ClNO2 varied between (0.035±0.027) and (1.38±0.60) with a campaign average of (0.49±0.35). The large variability in f reflects the highly variable chloride content of particles at the site. Uptake coefficients were also highly variable with minimum, maximum and average γ values of 0.004, 0.11 and 0.028±0.029, respectively, with no significant correlation with particle composition, but a weak dependence on relative humidity. The uptake coefficients obtained are compared to existing parameterizations based on laboratory datasets and with other values obtained by analysis of field data.
The term open-air factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties and attributed this to Criegee ...intermediates formed in the reaction of ozone with alkenes. We have re-evaluated those early experiments applying the current state of knowledge of ozone–alkene reactions. Contrary to previous speculation, neither Criegee intermediates nor the HO radicals formed in their decomposition are directly responsible for the germicidal activity attributed to the OAF. We identify other potential candidates, which are formed in ozone–alkene reactions and have known (and likely) germicidal properties, but the compounds responsible for the OAF remain a mystery. There has been very little research into the OAF since the 1970s, and this effect seems to have been largely forgotten. In this opinion piece we remind the community of the germicidal open-air factor. Given the current global pandemic spread by an airborne pathogen, understanding the natural germicidal effects of ambient air, solving the mystery of the open-air factor and determining how this effect can be used to improve human welfare should be a high priority for the atmospheric science community.
The uptake of hydrochloric acid (HCl), ethanol
(C2H5OH), 1-butanol (1-C4H9OH), formic acid HC(O)OH and
trifluoroacetic (CF3C(O)OH) acid to growing ice surfaces was
investigated at temperatures ...between 194 and 228 K. HCl displayed extensive,
continuous uptake during ice growth, which was strongly dependent on the ice
growth velocity, the temperature of the ice surface and the gas phase
concentration of HCl. Trifluoroacetic acid was also observed to be trapped
in growing ice, albeit approximately an order of magnitude less efficiently
than HCl, whereas the adsorption and desorption kinetics of ethanol,
1-butanol, formic acid on ice were not measurably different to those for
non-growing ice, even at very high ice growth rates. We present a
parameterisation of the uptake coefficient for HCl on growing ice films
(γtrap) and compare the results to an existing framework that
describes the non-equilibrium trapping of trace gases on ice. The trapping
of HCl in growing ice crystals in the atmosphere is assessed and compared to
the gas and ice phase partitioning resulting from equilibrium surface
adsorption and solubility.
We present the first ambient measurements of a new marine emission methane sulfonamide (MSAM: CH5NO2S), along with dimethyl sulfide (DMS) and dimethyl sulfone (DMSO2) over the Arabian Sea. Two ...shipborne transects (W → E, E → W) were made during the AQABA (Air Quality and Climate Change in the Arabian Basin) measurement campaign. Molar mixing ratios in picomole of species per mole of air (throughout this paper abbreviated as ppt) of DMS were in the range of 300–500 ppt during the first traverse of the Arabian Sea (first leg) and 100–300 ppt on the second leg. On the first leg DMSO2 was always below 40 ppt and MSAM was close to the limit of detection. During the second leg DMSO2 was between 40 and 120 ppt and MSAM was mostly in the range of 20–50 ppt with maximum values of 60 ppt. An analysis of HYSPLIT back trajectories combined with calculations of the exposure of these trajectories to underlying chlorophyll in the surface water revealed that most MSAM originates from the Somalia upwelling region, known for its high biological activity. MSAM emissions can be as high as one-third of DMS emissions over the upwelling region. This new marine emission is of particular interest as it contains both sulfur and nitrogen, making it potentially relevant to marine nutrient cycling and marine atmospheric particle formation.
The effect of water vapour on the rate coefficient for the atmospherically important, termolecular reaction between OH and NO2 was determined in He–H2O (277, 291, and 332 K) and N2–H2O bath gases ...(292 K). Combining pulsed-laser photolytic generation of OH and its detection by laser-induced fluorescence (PLP-LIF) with in situ, optical measurement of both NO2 and H2O, we were able to show that (in contrast to previous investigations) the presence of H2O increases the rate coefficient significantly. We derive a rate coefficient for H2O bath gas at the low-pressure limit (k0H2O) of 15.9×10-30 cm6 molecule-2 s-1. This indicates that H2O is a more efficient collisional quencher (by a factor of ≈6) of the initially formed HO–NO2 association complex than N2, and it is a factor of ≈8 more efficient than O2. Ignoring the effect of water vapour will lead to an underestimation of the rate coefficient by up to 15 %, e.g. in the tropical boundary layer. Combining the new experimental results from this study with those from our previous paper in which we report rate coefficients obtained in N2 and O2 bath gases (Amedro et al., 2019), we derive a new parameterization for atmospheric modelling of the OH + NO2 reaction and use this in a chemical transport model (EMAC) to examine the impact of the new data on the global distribution of NO2, HNO3, and OH. Use of the new parameters (rather than those given in the IUPAC and NASA evaluations) results in significant changes in the HNO3/NO2 ratio and NOx concentrations (the sign of which depends on which evaluation is used as reference). The model predicts the presence of HOONO (formed along with HNO3 in the title reaction) in concentrations similar to those of HO2NO2 at the tropical tropopause.
The radical terminating, termolecular reaction between OH and NO2 exerts great influence on the NOy∕NOx ratio and O3 formation in the atmosphere. Evaluation panels (IUPAC and NASA) recommend rate ...coefficients for this reaction that disagree by as much as a factor of 1.6 at low temperature and pressure. In this work, the title reaction was studied by pulsed laser photolysis and laser-induced fluorescence over the pressure range 16–1200 mbar and temperature range 217–333 K in N2 bath gas, with experiments at 295 K (67–333 mbar) for O2. In situ measurement of NO2 using two optical absorption set-ups enabled generation of highly precise, accurate rate coefficients in the fall-off pressure range, appropriate for atmospheric conditions. We found, in agreement with previous work, that O2 bath gas has a lower collision efficiency than N2 with a relative collision efficiency to N2 of 0.74. Using the Troe-type formulation for termolecular reactions we present a new set of parameters with k0(N2) = 2.6×10-30 cm6 molecule−2 s−1, k0(O2) = 2.0×10-30 cm6 molecule−2 s−1, m=3.6, k∞=6.3×10-11 cm3 molecule−1 s−1, and Fc=0.39 and compare our results to previous studies in N2 and O2 bath gases.
Formaldehyde (HCHO), hydrogen peroxide (H2O2)
and organic hydroperoxides (ROOH) play a key role in atmospheric oxidation
processes. They act as sources and sinks for HOx radicals
(OH + HO2), with OH ...as the primary oxidant that governs the
atmospheric self-cleaning capacity. Measurements of these species allow
for evaluation of chemistry-transport models which need to account for
multifarious source distributions, transport, complex photochemical reaction
pathways and deposition processes of these species. HCHO is an intermediate
during the oxidation of volatile organic compounds (VOCs) and is an indicator of photochemical activity
and combustion-related emissions. In this study, we use in situ observations
of HCHO, H2O2 and ROOH in the marine boundary layer (MBL) to
evaluate results of the general circulation model EMAC (ECHAM5/MESSy2
Atmospheric Chemistry; European Center HAMburg, Modular Earth Submodel System). The dataset was obtained during the Air Quality and Climate Change in the Arabian Basin (AQABA) ship
campaign around the Arabian Peninsula in summer 2017. This region is
characterized by high levels of photochemical air pollution, humidity and
solar irradiation, especially in the areas around the Suez Canal and the
Arabian Gulf. High levels of air pollution with up to 12 ppbv HCHO, 2.3 ppbv
ROOH and relatively low levels of H2O2 (≤0.5 ppbv) were
detected over the Arabian Gulf. We find that EMAC failed to predict absolute
mixing ratios of HCHO and ROOH during high-pollution events over the Arabian
Gulf, while it reproduced HCHO on average within a factor of 2. Dry
deposition velocities were determined for HCHO and H2O2 at
night with 0.77±0.29 cm s−1 for HCHO and 1.03±0.52 cm s−1 for H2O2 over the Arabian Sea, which were
matched by EMAC. The photochemical budget of H2O2 revealed
elevated HOx radical concentrations in EMAC, which resulted in an
overestimation of H2O2 by more than a factor of 5 for the AQABA
dataset. The underestimated air pollution over the Arabian Gulf was related
to EMAC's coarse spatial resolution and missing anthropogenic emissions in
the model.
We present shipborne measurements of NOx (≡ NO + NO2) and NOy (≡ NOx+ gas- and
particle-phase organic and inorganic oxides of nitrogen) in summer 2017 as
part of the expedition “Air Quality and ...climate change in the Arabian BAsin” (AQABA). The NOx and NOz (≡ NOy-NOx)
measurements, made with a thermal dissociation cavity ring-down spectrometer
(TD-CRDS), were used to examine the chemical mechanisms involved in the
processing of primary NOx emissions and their influence on the NOy
budget in chemically distinct marine environments, including the
Mediterranean Sea, the Red Sea, and the Arabian Gulf, which were influenced
to varying extents by emissions from shipping and oil and gas production.
Complementing the TD-CRDS measurements, NO and NO2 data sets from a
chemiluminescence detector (CLD) were used in the analysis. In all regions,
we find that NOx is strongly connected to ship emissions, both via
direct emission of NO and via the formation of HONO and its subsequent
photolytic conversion to NO. The role of HONO was assessed by calculating
the NOx production rate from its photolysis. Mean NO2 lifetimes
were 3.9 h in the Mediterranean Sea, 4.0 h in the Arabian Gulf, and
5.0 h in the Red Sea area. The cumulative loss of NO2 during the
night (reaction with O3) was more important than daytime losses
(reaction with OH) over the Arabian Gulf (by a factor 2.8) and over the Red
Sea (factor 2.9), whereas over the Mediterranean Sea, where OH levels were
high, daytime losses dominated (factor 2.5). Regional ozone production
efficiencies (OPEs; calculated from the correlation between Ox and
NOz, where Ox= O3+ NO2) ranged from 10.5 ± 0.9 to 19.1 ± 1.1. This metric quantifies the relative strength of
photochemical O3 production from NOx compared to the competing
sequestering into NOz species. The largest values were found over the
Arabian Gulf, consistent with high levels of O3 found in that region
(10–90 percentiles range: 23–108 ppbv). The fractional contribution of
individual NOz species to NOy exhibited a large regional
variability, with HNO3 generally the dominant component (on average
33 % of NOy) with significant contributions from organic nitrates
(11 %) and particulate nitrates in the PM1 size range (8 %).
We report the characteristics and performance of a newly developed five-channel cavity ring-down spectrometer to detect NO3, N2O5, NO2, total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs). ...NO3 and NO2 are detected directly at 662 and 405nm, respectively. N2O5 is measured as NO3 after thermal decomposition at 383K. PNs and ANs are detected as NO2 after thermal decomposition at 448 and 648K. We describe details of the instrument construction and operation as well as the results of extensive laboratory experiments that quantify the chemical and optical interferences that lead to biases in the measured mixing ratios, in particular involving the reactions of organic radical fragments following thermal dissociation of PNs and ANs. Finally, we present data obtained during the first field deployment of the instrument in July 2015.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Polycyclic aromatic hydrocarbons (PAHs) and their alkylated
(RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives are air
pollutants. Many of these substances are long-lived, can undergo ...long-range
atmospheric transport and adversely affect human health upon exposure.
However, the occurrence and fate of these air pollutants have hardly been
studied in the marine atmosphere. In this study, we report the atmospheric
concentrations over the Mediterranean Sea, the Red Sea, the Arabian Sea, the
Gulf of Oman and the Arabian Gulf, determined during the AQABA (Air Quality
and Climate Change in the Arabian Basin) project, a comprehensive ship-borne
campaign in summer 2017. The average concentrations of ∑26PAHs,
∑19RPAHs, ∑11OPAHs and ∑17NPAHs, in the gas
and particulate phases, were 2.99 ± 3.35 ng m−3, 0.83 ± 0.87 ng m−3, 0.24 ± 0.25 ng m−3 and 4.34 ± 7.37 pg m−3, respectively. The Arabian Sea region was the cleanest for all
substance classes, with concentrations among the lowest ever reported. Over
the Mediterranean Sea, we found the highest average burden of ∑26PAHs and ∑11OPAHs, while the ∑17NPAHs were
most abundant over the Arabian Gulf (known also as the Persian Gulf).
1,4-Naphthoquinone (1,4-O2NAP) followed by 9-fluorenone and
9,10-anthraquinone were the most abundant studied OPAHs in most samples. The
NPAH composition pattern varied significantly across the regions, with
2-nitronaphthalene (2-NNAP) being the most abundant NPAH. According to
source apportionment investigations, the main sources of PAH derivatives in
the region were ship exhaust emissions, residual oil combustion and
continental pollution. All OPAHs and NPAHs except 2-nitrofluoranthene (2-NFLT), which were
frequently detected during the campaign, showed elevated concentrations in
fresh shipping emissions. In contrast, 2-NFLT and
2-nitropyrene (2-NPYR) were highly abundant in aged shipping emissions due
to secondary formation. Apart from 2-NFLT and 2-NPYR,
benz(a)anthracene-7,12-dione and 2-NNAP also had significant photochemical
sources. Another finding was that the highest concentrations of PAHs, OPAHs
and NPAHs were found in the sub-micrometre fraction of particulate matter
(PM1).
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