High- and low-temperature pyrolysis profiles describe volatile organic compound emissions from western US wildfire fuels Atmospheric Chemistry and Physics DOI 10.5194/acp-18-9263-2018 3 July 2018 We found that on average 85 % of the VOC emissions from biomass burning across various fuels representative of the western US (including various coniferous and chaparral fuels) can be explained using only two emission profiles: (i) a high-temperature pyrolysis profile and (ii) a low-temperature pyrolysis profile. The high-temperature profile is quantitatively similar between different fuel types (r2 > 0.84), and likewise for the low-temperature profile. Read more
Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations Atmospheric Chemistry and Physics DOI 10.5194/acp-18-8409-2018 15 June 2018 We analyse simulations from the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion by anthropogenic chlorine and bromine. The simulations from 20 models project that global column ozone will return to 1980 values in 2047 (uncertainty range 2042–2052). Return dates in other regions vary depending on factors related to climate change and importance of chlorine and bromine. Column ozone in the tropics may continue to decline. Read more
Surface impacts of the Quasi Biennial Oscillation Atmospheric Chemistry and Physics DOI 10.5194/acp-18-8227-2018 13 June 2018 A major phenomenon in the stratosphere is the Quasi Biennial Oscillation (QBO). Although a feature of the equatorial stratosphere, its influence extends to surface weather at both equatorial and mid latitudes. Improved knowledge of mechanisms of influence should help to improve weather forecasts. In this paper, QBO impacts at the surface are characterized and dominant mechanisms explored. Three pathways are identified, referred to as the tropical, subtropical and polar routes. Read more
On ozone trend detection: using coupled chemistry–climate simulations to investigate early signs of total column ozone recovery Atmospheric Chemistry and Physics DOI 10.5194/acp-18-7625-2018 1 June 2018 2017 marks the 30th anniversary of the Montreal Protocol, which was implemented to protect the stratospheric ozone layer from the harmful effects of synthetic ozone depleting substances. Since the late 1990s atmospheric concentrations of these species have begun to decline, and as a result ozone concentrations are expected to increase. In this study we use an ensemble of chemistry–climate simulations to investigate recent ozone trends and search for early signs of ozone recovery. Read more
Contrails and their impact on shortwave radiation and photovoltaic power production – a regional model study Atmospheric Chemistry and Physics DOI 10.5194/acp-18-6393-2018 7 May 2018 A numerical model also used for operational weather forecast was applied to investigate the impact of contrails and contrail cirrus on the radiative fluxes at the earth’s surface. Accounting for contrails produced by aircraft enables the model to simulate high clouds that are otherwise missing. In a case study, we find that the effect of these extra clouds is to reduce the incoming shortwave radiation at the surface as well as the production of photovoltaic power by up to 10 %. Read more
Global evaluation and calibration of a passive air sampler for gaseous mercury Atmospheric Chemistry and Physics DOI 10.5194/acp-18-5905-2018 26 April 2018 A new passive air sampler for gaseous mercury was tested at 20 sites on four continents. These sites have in common that they use the state-of-the-art active air sampling technique for gaseous mercury on a continuous basis and therefore allow for an evaluation and calibration of the passive sampler. The sampler proved to work exceptionally well, with a precision and accuracy on par with the active instrument and better than what has previously been achieved with passive samplers. Read more
Novel pathway of SO2 oxidation in the atmosphere: reactions with monoterpene ozonolysis intermediates and secondary organic aerosol Atmospheric Chemistry and Physics DOI 10.5194/acp-18-5549-2018 24 April 2018 Synergistic effects between SOA formation and SO2 oxidation through Criegee chemistry and reactive uptake by organic peroxides were observed. The relative importance of these two pathways (Criegee vs. peroxide) varies with relative humidity. The latter SO2 loss mechanism to organic peroxides in SOA has not previously been identified. Our results suggest a new pathway of atmospheric SO2 oxidation, which may contribute to the missing mechanisms of high-sulfate production in the polluted areas. Read more
Using satellite measurements of N2O to remove dynamical variability from HCl measurements Atmospheric Chemistry and Physics DOI 10.5194/acp-18-5691-2018 24 April 2018 Detecting trends in short data sets of stratospheric molecules is difficult because of variability due to dynamical fluctuations. We suggest that one way around this difficulty is using the measurements of one molecule to remove dynamical variability from the measurements of another molecule. We illustrate this using Aura MLS measurements of N2O to help us sort out issues in the determination of trends in HCl. This shows that HCl is decreasing throughout the middle stratosphere as expected. Read more
Considering the future of anthropogenic gas-phase organic compound emissions and the increasing influence of non-combustion sources on urban air quality Atmospheric Chemistry and Physics DOI 10.5194/acp-18-5391-2018 20 April 2018 Following decades of successful regulatory policies focused on combustion-related sources (e.g. motor vehicles), emissions from non-combustion sources have become increasingly important for urban air quality. Using multiple approaches, we demonstrate that emissions from consumer, commercial, and industrial products and materials have become prominent contributors to the formation of photochemical smog (i.e. secondary organic particulate matter and ozone) and its associated health effects. Read more
Evaluation of stratospheric age of air from CF4, C2F6, C3F8, CHF3, HFC-125, HFC-227ea and SF6; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials Atmospheric Chemistry and Physics DOI 10.5194/acp-18-3369-2018 8 March 2018 Chemical species measured in stratospheric air can be used as proxies for stratospheric circulation changes which cannot be measured directly. A range of tracers is important to understand changing stratospheric dynamics. We demonstrate the suitability of PFCs and HFCs as tracers and support recent work that reduces the current stratospheric lifetime of SF6. Updates to policy-relevant parameters (e.g. stratospheric lifetime) linked to this change are provided for O3-depleting substances. HFC-125, HFC-227ea and SF6; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials">Read more
