Suppression of surface ozone by an aerosol-inhibited photochemical ozone regime

TY - JOUR

T1 - Suppression of surface ozone by an aerosol-inhibited photochemical ozone regime

AU - Ivatt, Peter David

AU - Evans, Mathew John

AU - Lewis, Alastair

N1 - © The Author(s) 2022

PY - 2022/7/7

Y1 - 2022/7/7

N2 - Atmospheric ozone (O3) is a pollutant produced through chemical chain reactions where volatile organic compounds (VOCs), carbon monoxide and methane are oxidized in the presence of oxides of nitrogen (NOx). For decades, the controlling chain termination step has been used to separate regions into either ‘NOx limited’ (peroxyl-radical self-reactions dominate) or ‘VOC limited’ (hydroxyl radical (OH) + nitrogen dioxide (NO2) reaction dominates). The controlling regime would then guide poli- cies for reducing emissions and so O3 concentrations. Using a chemical transport model, we show that a third ‘aerosol inhib- ited’ regime exists, where reactive uptake of hydroperoxyl radicals (HO2) onto aerosol particles dominates. In 1970, 2% of the Northern Hemisphere population lived in an aerosol-inhibited regime, but by 2014 this had increased to 21%; 60% more than lived in a VOC-limited regime. Aerosol-inhibited chemistry suppressed surface O3 concentrations in North America and Europe in the 1970s and is currently suppressing surface O3 over Asia. This third photochemical O3 regime leads to potential trade-off tensions between reducing particle pollution in Asia (a key current health policy and priority) and increasing surface O3, should O3 precursors emissions not be reduced in tandem.

AB - Atmospheric ozone (O3) is a pollutant produced through chemical chain reactions where volatile organic compounds (VOCs), carbon monoxide and methane are oxidized in the presence of oxides of nitrogen (NOx). For decades, the controlling chain termination step has been used to separate regions into either ‘NOx limited’ (peroxyl-radical self-reactions dominate) or ‘VOC limited’ (hydroxyl radical (OH) + nitrogen dioxide (NO2) reaction dominates). The controlling regime would then guide poli- cies for reducing emissions and so O3 concentrations. Using a chemical transport model, we show that a third ‘aerosol inhib- ited’ regime exists, where reactive uptake of hydroperoxyl radicals (HO2) onto aerosol particles dominates. In 1970, 2% of the Northern Hemisphere population lived in an aerosol-inhibited regime, but by 2014 this had increased to 21%; 60% more than lived in a VOC-limited regime. Aerosol-inhibited chemistry suppressed surface O3 concentrations in North America and Europe in the 1970s and is currently suppressing surface O3 over Asia. This third photochemical O3 regime leads to potential trade-off tensions between reducing particle pollution in Asia (a key current health policy and priority) and increasing surface O3, should O3 precursors emissions not be reduced in tandem.

U2 - 10.1038/s41561-022-00972-9

DO - 10.1038/s41561-022-00972-9

M3 - Article

SN - 1752-0894

VL - 15

SP - 536

EP - 540

JO - Nature Geoscience

JF - Nature Geoscience

ER -