An Estimation of the Levels of Stabilized Criegee Intermediates in the UK Urban and Rural Atmosphere Using the Steady-State Approximation and the Potential Effects of These Intermediates on Tropospheric Oxidation Cycles

Abstract

Levels of the stabilized Criegee Intermediate (sCI), produced via the ozonolysis of unsaturated volatile organic compounds (VOCs), were estimated at two London urban sites (Marylebone Road and Eltham) and one rural site (Harwell) in the UK over the period of 1998–2012. The steady‐state approximation was applied to data obtained from the NETCEN (National Environmental Technology Centre) database, and the levels of annual average sCI were estimated to be in the range of 30–3000 molecules cm−3 for UK sites. A consistent diurnal cycle of sCI concentration is estimated for the UK sites with increasing levels during daylight hours, peaking just after midday. The seasonal pattern of sCI shows higher levels in spring with peaks around May due to the higher levels of O3. The ozone weekend effect resulted in higher sCI in UK urban areas during weekend. The sCI data were modeled using the information provided by the Air Quality Improvement Research Program (AQIRP) and found that the modeled production was five‐ to six‐fold higher than our estimated data, and therefore the estimated sCI concentrations in this study are thought to be lower estimates only. Compared with nighttime, 1.3‐ to 1.8‐fold higher sCI exists under daytime conditions. Using the levels of sCI estimated at Marylebone Road, globally the oxidation rates of NO2 + sCI (22.4 Gg/yr) and SO2 + sCI (37.6 Gg/yr) in urban areas can increase their effect in the troposphere and potentially further alter the oxidizing capacity of the troposphere. Further investigations of modeled sCI show that CH3CHOO (64%) and CH2OO (13%) are dominant among all contributing sCI at the UK sites.

Investigating the Tropospheric Chemistry of Acetic Acid Using the Global 3‐D Chemistry Transport Model, STOCHEM‐CRI

“…A limited number of olefins producing CH 3 COOH through Criegee intermediate, CH 3 CHOO formation, are used in the model because of the lack of their emission inventories. Khan, Morris, et al () found the most abundant Criegee to be CH 3 CHOO (73%) among all other Criegee Intermediates in the UK urban environment. The dominating precursors of CH 3 CHOO were found in their study to be 2‐methyl‐2‐butene (49%), trans‐2‐butene (17%), cis‐2‐butene (11%), trans‐2‐pentene (5%), propene (5%), cis‐2‐pentene (2%), 4‐methyl‐trans‐2‐pentene (2%), 3‐methyl‐trans‐2‐pentene (2%), 3‐methyl‐cis‐2‐pentene (3%), and trans‐2‐hexene (1%).…”

Criegee intermediates and their impacts on the troposphere

“…Figure 7. The hourly, monthly, and daily estimated sCI concentrations in the two urban sites and one rural site of UK (Adapted from Khan et al 105 ). The error bars represents ± 1 SD of the whole data series.…”

Unimolecular decay strongly limits the atmospheric impact of Criegee intermediates

“…The modeling studies currently available in the literature [17][18][19][20][21][22]54,65 did not have access to sufficiently detailed information, and of necessity adopted identical rate coefficients for very diverse families of SCI, resulting in large uncertainties and large variations across the SCI concentration predictions. Based on the rate coefficients obtained above for unimolecular reactions and reaction with H 2 O and (H 2 O) 2 , combined with sitespecific ozonolysis rates from literature, and field measurement data [33][34][35][36] on the relevant VOC, O 3 , NO 2 , SO 2 , carboxylic acid, and H 2 O concentrations, the speciated steady-state SCI concentration can then be estimated.…”

“…The production rates and the contribution in the total SCI formation are given for sites with mostly biogenic emissions (Amazonia and Sierra Nevada combined), and for a site with mostly anthropogenic emission (Mexico city stark contrast to early estimates that predicted up to 800% increase in SO 2 oxidation in some regions, but are in line with more recent modeling estimates. 18,22 Further studies are needed to investigate the subsequent impact of SCI-induced H 2 SO 4 formation on the nucleation rates or aerosol chemistry in these regions. Fig.…”

“…Several studies tried to estimate the SCI concentration and/or its impact on aerosol formation, by modeling or by examining related processes, but lack of data limits their reliability. [17][18][19][20][21][22] In this work, we theoretically examine over 200 CI reactions, spanning a large range of substitutions: H-atoms, linear and branched aliphatic groups, b-and g-unsaturated substituents, as well as oxo-and OH-substituents (see Fig. 2).…”