Browsing by Author "Holland, Rayne"

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    Elucidating the effects of covid-19 lockdowns in the UK on the o3-nox-voc relationship
    (Multidisciplinary Digital Publishing Institute (MDPI), 2024) Shallcross, Dudley; Holland, Rayne; Seifert, Katya
    The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O3) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NOx (NO+NO2) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O3 fluctuations. Compared with pre-lockdown levels, NO and NO2 declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O3 levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO2] ratio for O3 concentration response. Analysis of the response of O3 concentrations to the NOx reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NOx-limited. This was in agreement with the [VOC]/[NOx] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NOx] ratios for the London Eltham (LE; suburban background) site indicated NOx-sensitivity, which may suggest the [VOC]/[NOx] ratio for O3 concentration response may have had a slight NOx-sensitive bias. Furthermore, O3 concentration response with [NO]/[NO2] and [VOC]/[NOx] were also investigated to determine their relevance and accuracy in identifying O3-NOx-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O3 during this period was primarily driven by shifts in oxidant (OX; NO2 + O3) equilibrium as a result of decreasing NO2, with increased O3 transported from Europe likely having some influence.
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    Investigating the variation of benzene and 1,3 butadiene in the UK during 2000–2020
    (MDPI, 2022) Holland, Rayne; Khan, M. Anwar H.; Shallcross, Dudley E.
    The concentrations of benzene and 1,3-butadiene in urban, suburban, and rural sites of the U.K. were investigated across 20 years (2000–2020) to assess the impacts of pollution control strategies. Given the known toxicity of these pollutants, it is necessary to investigate national long-term trends across a range of site types. We conclude that whilst legislative intervention has been successful in reducing benzene and 1,3-butadiene pollution from vehicular sources, previously overlooked sources must now be considered as they begin to dominate in contribution to ambient pollution. Benzene concentrations in urban areaswere found to be ~5-fold greater than those in rural areas,whilst 1,3-butadiene concentrations were up to ~10-fold greater.
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    Investigation of organic hydrotrioxide (roooh) formation from ro2 + oh reactions and their atmospheric impact using a chemical transport model, stochem-cri
    (Royal Society of Chemistry, 2025) Shallcross, Dudley E; Khan, Md Anwar Hossain; Holland, Rayne
    Incorporating the reactions of fifty peroxy radicals (RO2) with the hydroxyl radical (OH) into the global chemistry transport model, troposphere, affected the composition of the troposphere by changing the global burdens of NOx (−2.7 Gg, −0.5%), O3 (−2.3 Tg, −0.7%), CO (−3.2 Tg, −0.8%), HOx (+2.1 Gg, +7.7%), H2O2 (+0.5 Tg, +18.3%), RO2 (−8.0 Gg, −18.2%), RONO2 (−19.4 Gg, −4.7%), PAN (−0.1 Tg, −3.4%) HNO3 (−7.4 Gg, −1.3%) and ROOH (−96.9 Gg, −3.8%). The RO2 + OH addition reactions have a significant impact on HO2 mixing ratios in tropical regions with up to a 25% increase, resulting in increasing H2O2 mixing ratios by up to 50% over oceans. Globally, a significant amount of organic hydrotrioxides (ROOOH) (86.1 Tg per year) are produced from these reactions with CH3OOOH (67.5 Tg per year, 78%), isoprene-derived ROOOH (5.5 Tg per year, 6%) and monoterpene-derived ROOOH (4.2 Tg per year, 5%) being the most significant contributors. The tropospheric global burden of CH3OOOH is found to be 0.48 Gg. The highest mixing ratios of ROOOH, of up to 0.35 ppt, are found primarily in the oceans near the tropical land areas. The RO2 + OH reactions have a small, but noticeable, contribution to OH reactivity (∼5%) over tropical oceans. Additionally, these reactions have a significant impact on RO2 reactivity over tropical oceans where losses of the CH3O2 radical, isoprene derived peroxy radical (ISOPO2) and monoterpene derived peroxy radical (MONOTERPO2) by OH can contribute up to 25%, 15% and 50% to the total RO2 loss, respectively. The changes in RO2 reactivity influence the global abundances of organic alcohols (ROH) which are important species due to their crucial impact on air quality. The ROOOH generate secondary organic aerosol (SOA) of up to 0.05 μg m−3 which affects the Earth's radiation budget because of enhancing modelled organic aerosol by up to 5% and 2000% on land surfaces and the remote tropical oceans, respectively.