Browsing by Author "Shallcross, Dudley E"

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    Electrical environment can be altered at 1 km distances from high voltage power lines.
    (Institute of Physics, 2024) Matthews, James C.; Shallcross, Dudley E
    High voltage powerlines emit electrical charges into the atmosphere which can then attach to aerosols. This space charge above ground can be measured directly using ion spectrometers or indirectly through perturbations of the Earth's potential gradient using field mills. Several publications are reviewed to find evidence of aerosol charging at a distance from power lines. Field measurements of charge state near to high voltage power lines selected due to their high emissions of ions measured a small positive enhancement of electrical charge on aerosols at distances greater than 300 m, corresponding to a transit time of up to 400 s A quasi one-dimensional model of ion-aerosol interactions from a high voltage powerlines found that the addition of new ions to an aerosol population will result in those ions transferring charge to the aerosol which would then remain the dominant carrier of charge several hundred meters downwind. 10-min PG measurements from a fixed site measuring in 2008 compared measurements when the site was downwind of a 275 kV powerline to times with no wind and found evidence of space charge overhead through greater fields and variability at distances over 800 m These studies combined show evidence that the electrical environment near to power lines can be altered beyond 1 km from AC high voltage power lines, with excess charges likely to be concentrated on aerosol.
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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.
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    Particle number concentration measurements on public transport in Bangkok, Thailand
    (Multidisciplinary Digital Publishing Institute (MDPI), 2023) Shallcross, Dudley E; Matthews, James C; Chalida, Chompoobut; Navasumrit, Panida
    Traffic is a major source of particulate pollution in large cities, and particulate matter (PM) level in Bangkok often exceeds the World Health Organisation limits. While PM2.5 and PM10 are both measured in Bangkok regularly, the sub-micron range of PM, of specific interest in regard to possible adverse health effects, is very limited. In the study, particle number concentration (PNC) was measured on public transport in Bangkok. A travel route through Bangkok using the state railway, the mass rapid transport underground system, the Bangkok Mass Transit System (BTS) Skytrain and public buses on the road network, with walking routes between, was taken whilst measuring particle levels with a hand-held concentration particle counter. The route was repeated 19 times covering different seasons during either morning or evening rush hours.