Investigation of organic hydrotrioxide (ROOOH) formation from RO2 + OH reactions and their atmospheric impact using a chemical transport model, STOCHEM-CRI†

Abstract

Incorporating the reactions of fifty peroxy radicals (RO₂) with the hydroxyl radical (OH) into the global chemistry transport model, STOCHEM-CRI, affected the composition of the troposphere by changing the global burdens of NO_x (−2.7 Gg, −0.5%), O₃ (−2.3 Tg, −0.7%), CO (−3.2 Tg, −0.8%), HO_x (+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.