We present an instrument for the measurement of total ozone
reactivity – the reciprocal of the chemical lifetime of ozone
(O3) – in the troposphere. The Total Ozone Reactivity
System (TORS) was ...developed with the objective to study the role of
biogenic volatile organic compounds (BVOCs) as chemical sinks of
tropospheric ozone. The instrument was extensively characterized and
tested in the laboratory using individual BVOCs and small plants
(lemon thyme, Thymus citriodorus) in a Teflon bag and proved
able to measure reactivities corresponding to >4.5×10-5
s−1 (at 5 min averaging time), with an estimated total
uncertainty of ∼32%. Such reactivities correspond to >20 ppb of α-pinene or >150 ppb of isoprene in
isolation – larger than typical ambient levels but observable in
environmental chamber and enclosure experiments as well as in
BVOC-rich environments. The functionality of TORS was demonstrated
in quasi-ambient conditions with a deployment in a horticultural
glasshouse containing a range of aromatic plants. The measurements
of total ozone reactivity made in the glasshouse showed a clear
diurnal pattern, following the emissions of BVOCs, and are consistent
with mixing ratios of tens of parts per billion of monoterpenes and several
parts per billion of sesquiterpenes.
The organic content of shale has become of commercial interest as a source of hydrocarbons, owing to the development of hydraulic fracturing (“fracking”). While the main focus is on the extraction of ...methane, shale also contains significant amounts of non-methane hydrocarbons (NMHCs). We describe the first real-time observations of the release of NMHCs from a fractured shale. Samples from the Bowland-Hodder formation (England) were analyzed under different conditions using mass spectrometry, with the objective of understanding the dynamic process of gas release upon fracturing of the shale. A wide range of NMHCs (alkanes, cycloalkanes, aromatics, and bicyclic hydrocarbons) are released at parts per million or parts per billion level with temperature- and humidity-dependent release rates, which can be rationalized in terms of the physicochemical characteristics of different hydrocarbon classes. Our results indicate that higher energy inputs (i.e., temperatures) significantly increase the amount of NMHCs released from shale, while humidity tends to suppress it; additionally, a large fraction of the gas is released within the first hour after the shale has been fractured. These findings suggest that other hydrocarbons of commercial interest may be extracted from shale and open the possibility to optimize the “fracking” process, improving gas yields and reducing environmental impacts.
We used a one-dimensional model to simulate the chemical evolution of air masses in the tropical Atlantic Ocean, with a focus on halogen chemistry. The model results were compared to the observations ...of inorganic halogen species made in this region. The model could largely reproduce the measurements of most chlorine species, especially under unpolluted conditions, but overestimated sea salt chloride, BrCl, and bromine species. Agreement with the measurements could be improved by taking into account the reactivity with aldehydes and the effects of dimethyl sulfide (DMS) and Saharan dust on aerosol pH; a hypothetical HOX → X– aqueous-phase reaction could also improve the agreement with measured Cl2 and HOCl, especially under semipolluted conditions. The results also showed that halogens speciation and concentrations are very sensitive to cloud processing. The model was used to calculate the impact of the observed levels of halogens: Cl atoms accounted for 5.4–11.6% of total methane sinks and halogens (mostly bromine and iodine) accounted for 35–40% of total ozone destruction.
Nitrogen oxides (NO and NO2, collectively NOX) derived from vehicle exhausts are critical pollutants with significant implications for urban air quality and human and environmental health. In this ...study, we investigate trends in measured ambient nitrogen dioxide (NO2) and NOx mixing ratios at urban traffic - dominated monitoring sites in the UK for the period 2009–2016. We apply an oxidant analysis approach alongside a number of assumptions to the ambient data to determine trends in the inferred primary NO2/NOx ratio, and examine evidence for enhanced vehicle “cold start” effects upon these inferred emissions. Ambient NO2 and NOX mixing ratios have experienced an overall decrease of 17.2% and 11.3% respectively for the locations considered over this time period. The inferred primary NO2/NOx ratio for the majority of the study locations is found to have fallen by 29% (from 0.175 to 0.125) as a monthly mean from 2009 to 2016, with a statistically significant median decrease of 0.32 percentage points per year. However, during cold weather (temperatures less than or equal to 5 OC), the inferred primary NO2/NOx ratio averaged across all locations, when compared with normal conditions (temperatures higher than 5 OC) increased from 0.062 (±0.004) to 0.102 (±0.001) (64.5% higher) and from 0.056 (±0.004) to 0.098 (±0.001) (75% higher) for cold morning and evening rush hours, with substantially greater increases at some sites. This “cold start” result suggests that the combination of recent vehicle driving history and ambient weather conditions, in conjunction with technological constraints on the operating temperature range of emission control systems in some vehicles, affects NOx emissions and hence has a detrimental impact upon air quality in urban environments. Increased cold start emissions imply an increased NO2 - derived health burden from air pollution, under certain meteorological conditions, assessment of which should consider changes in vehicle use as a result of weather, and hence altered personal exposure.
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•A methodology is developed to assess enhanced “cold-start” primary NO2 emissions from vehicles.•Ambient mixing ratios of NO2 and NOx measured at UK urban traffic sites have fallen over the period from 2009 to 2016.•Inferred primary NO2/NOx ratio experiences a statistically significant decrease from 17.5% to 12.5% between 2009 and 2016.•Inferred cold-start primary NO2 vehicle emissions are significantly higher than those found under warmer conditions.•Inferred cold-start primary NO2 vehicle emissions have measurable impacts upon urban air quality in the UK.
The nitrate radical, NO3, and dinitrogen pentoxide, N2O5, are key reactive nocturnal nitrogen oxides in the troposphere. The daytime impact of NO3 and N2O5, however, is restricted by photochemical ...recycling of NO3 to NO2 and O3. In this paper, we report daytime measurements of N2O5 on board the NOAA research vessel Ronald H. Brown in the Gulf of Maine during the New England Air Quality Study–Intercontinental Transport and Chemical Transformation (NEAQS‐ITCT) campaign in the summer of 2004. Daytime N2O5 mixing ratios of up to 4 pptv were observed, consistent with predictions from a steady state analysis. Predicted and observed NO3 mixing ratios were below the instrumental detection limit of ∼1 pptv; the average calculated concentration was 0.09 pptv. Important impacts of daytime NO3 and N2O5 in the marine boundary layer included increased rates of VOC oxidation (in particular dimethyl sulfide) and enhanced NOx to HNO3 conversion, both of which scaled with the available NOx. Smaller effects of daytime NO3 and N2O5 included chemical destruction of O3 and a shift of the NO2:NO ratio. Because the rates of heterogeneous conversion of N2O5 and NO3 to HNO3 scale with the surface area available for uptake, the importance of daytime fog is discussed.
Vehicle use, as driver or passenger, is a key transport mode and important microenvironment for personal exposure to air pollutants. Here, the air pollution exposure of vehicle occupants, relative to ...external, ambient levels was explored under different vehicle ventilation settings and driving routes in an urban area. Four vehicles were driven on a consistent route encompassing three contrasting road types, measuring simultaneous within-vehicle and ambient levels of particulate matter (PM10, PM2.5, PM1), ultrafine particles number (UFP), lung surface deposited area (LSDA), nitric oxide (NO) and nitrogen dioxide (NO2). For the majority of ventilation settings available, the inside/outside (I/OVEH) ratio for PM10, PM2.5, PM1, UFP, LSDA and NO2 concentrations was below 1, with the exception of NO, for which the ratio was independent of ventilation settings, within uncertainty. The lowest within-vehicle exposure for particles and gases was observed under the conditions of windows closed, recirculation and air conditioning on. Vehicle occupants are exposed to and inhale more air pollution when traveling on urban roads, followed by ring-roads and sub-urban roads. However, through reduced within-vehicle concentrations and reduced physical activity and hence breathing rate, they inhale less air pollution than people cycling/walking on the same routes. Within-vehicle air pollution exposure displays significant dependence upon both the ventilation setting and route selected. Vehicle occupants can, therefore, modify their personal exposure through these choices. Finally, vehicle occupants inhale more mass of NO2 than PM2.5 with a trip-average inhalation dose ratio of 6.4 (NO2 dose/PM2.5 dose). These results may have significant health impacts upon highly exposed groups such as professional drivers.
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•Investigation of within-vehicle cabin NOx and particle exposure of occupants.•Exposure variation with outside air quality, ventilation settings and route choice.•Overall median inside/outside vehicle air pollutants exposure: PM2.5: 0.76, NO2: 0.98•Exposure reduction for optimal ventilation settings: PM2.5 by 49%, NO2 by 34%.•Median inhalation NO2/PM2.5 dose ratio: urban: 4.6, sub-urban: 7.6, ring road: 6.9
Mixing ratios of dimethyl sulfide (DMS) and its nighttime oxidant, the nitrate radical (NO3), were measured in the summertime marine boundary layer (MBL) of the Gulf of Maine during the New England ...Air Quality Study–International Transport and Chemical Transformation campaign in 2004. DMS fluxes from the ocean were derived from simultaneous measurements of the wind speed and DMS in seawater. Day and night DMS oxidation rates were determined from modeled OH and measured NO3 concentrations. The average DMS lifetime with respect to oxidation by OH at noon was 13.5 ± 3.4 (1σ) h, while at night, DMS lifetimes with respect to NO3 oxidation varied by sampling region from 11 min to 28 h. Oxidation by photochemically generated halogen species likely also played a role during the day, although the nature and extent of the halogen species is more difficult to predict due to lack of halogen measurements. Closure of the DMS budget in the MBL required a vertical entrainment velocity of ∼0.4 cm s−1. This study suggests that entrainment of DMS out of the MBL competes with daytime oxidation and that the presence of pollution in the form of NOx and O3 in near‐coastal regions at night results in nearly complete DMS oxidation within the MBL via reaction with NO3, with a much smaller contribution from entrainment. One potential implication of near‐complete DMS oxidation within the MBL is a reduction of the amount of sulfur available for aerosol formation and growth at higher altitudes in the atmosphere.
Which published papers have transformed our understanding of the chemical processes in the troposphere and shaped the field of atmospheric chemistry? By way of expert solicitation and interactive ...peer review, this paper explores the influence of the ideas in peer-reviewed articles based on input from our community of atmospheric scientists. We explore how these papers have shaped the development of the field of atmospheric chemistry and identify the major landmarks in the field of atmospheric chemistry through the lens of those papers' impact on science, legislation and environmental events. We also explore the ways in which one can identify the papers that have most impacted the field and discuss the advantages and disadvantages of the various approaches. Our work highlights the difficulty of creating a simple list, and we explore the reasons for this difficulty. The paper also provides a history of the development of our understanding of tropospheric chemistry and points some ways for the future.
Carbonyl sulfide (OCS), the most abundant sulfur gas in
the Earth's atmosphere, is a greenhouse gas, a precursor to stratospheric
sulfate aerosol, and a proxy for terrestrial CO2 uptake. Estimates of
...important OCS sources and sinks still have significant uncertainties and the
global budget is not considered closed. One particularly uncertain source
term, the OCS production during the atmospheric oxidation of dimethyl
sulfide (DMS) emitted by the oceans, is addressed by a series of experiments
in the atmospheric simulation chamber SAPHIR in conditions comparable to the
remote marine atmosphere. DMS oxidation was initiated with OH and/or Cl
radicals and DMS, OCS, and several oxidation products and intermediates were
measured, including hydroperoxymethyl thioformate (HPMTF), which was recently
found to play a key role in DMS oxidation in the marine atmosphere. One
important finding is that the onset of HPMTF and OCS formation occurred
faster than expected from the current chemical mechanisms. In agreement with
other recent studies, OCS yields between 9 % and 12 % were observed in our
experiments. Such yields are substantially higher than the 0.7 % yield
measured in laboratory experiments in the 1990s, which is generally used to
estimate the indirect OCS source from DMS in global budget estimates.
However, we do not expect the higher yields found in our experiments to
directly translate into a substantially higher OCS source from DMS oxidation
in the real atmosphere, where conditions are highly variable, and, as pointed
out in recent work, heterogeneous HPMTF loss is expected to effectively
limit OCS production via this pathway. Together with other experimental
studies, our results will be helpful to further elucidate the DMS oxidation
chemical mechanism and in particular the paths leading to OCS formation.
Methanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also ...contributes to aerosol mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation, climate change impact and regional transport. Here, we applied a validated quantification method to determine the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and North Atlantic Ocean, between 55 °N and 68 °N (26th May to June 23, 2022). With this method, the concentrations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that the average MSA concentration was 0.025 ± 0.03 μg m−3, ranging from <0.01 to 0.32 μg m−3. The lowest MSA level was found towards the northern leg of the cruise (near Sisimut (67 °N)) with air masses from sea ice over the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked in the afternoon, about one hour later than that of peak of solar radiation, which suggests that photochemical process is an important mechanism for the conversion of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a temperature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we found that the MSA/nss-SO4 ratio is around 0.22-0.25 in the remote northern marine atmosphere.
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•A validated quantification method was employed to determine the particulate MSA mass concentration by HR-TOF-AMS.•The OH-initiated pathway is an important mechanism for the conversion of DMS into MSA above the remote ocean.•Mass ratio of MSA to nss-SO4 presents temperature dependence during the whole cruise.
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