Trends in stabilisation of Criegee intermediates from alkene ozonolysis

Criegee Intermediates (CI), formed in the ozonolysis of alkenes, play a central role in tropospheric chemistry as an important source of radicals, with stabilised CI (SCI) able to participate in bimolecular reactions, affecting climate through the formation of inorganic and organic aerosol. However, total SCI yields have only been determined for a few alkene systems, while speciated SCI yields from asymmetrical alkenes are almost entirely unknown. Here we report for the first time a systematic experimental exploration of the stabilisation of CH2OO and (CH3)2COO CI, formed from ten alkene–ozone systems with a range of different sizes and structures, under atmospherically relevant conditions in the EUPHORE chamber. Experiments in the presence of excess SO2 (an SCI scavenger) determined total SCI yields from each alkene–ozone system. Comparison of primary carbonyl yields in the presence/absence of SO2 determined the stabilisation fraction of a given CI. The results show that the stabilisation of a given CI increases as the size of the carbonyl co-product increases. This is interpreted in terms of the nascent population of CI formed following decomposition of the primary ozonide (POZ) having a lower mean energy distribution when formed with a larger carbonyl co-product, as more of the energy from the POZ is taken by the carbonyl. These findings have significant implications for atmospheric modelling of alkene ozonolysis. Higher stabilisation of small CI formed from large alkenes is expected to lead to lower radical yields from CI decomposition, and higher SCI concentrations, increasing the importance of SCI bimolecular reactions

Kinetics of stabilised Criegee intermediates derived from alkene ozonolysis: reactions with SO2, H2O and decomposition under boundary layer conditions

The removal of SO2in the presence ofcis-but-2-ene and ozone exhibits a strong dependence on the water vapour concentration.</p

Interference from alkenes in chemiluminescent NOx measurements

Nitrogen oxides (NOx=NO + NO2) are critical intermediates in atmospheric chemistry and air pollution. NOx levels control the cycling and hence abundance of the primary atmospheric oxidants OH and NO3 and regulate the ozone production which results from the degradation of volatile organic compounds (VOCs) in the presence of sunlight. They are also atmospheric pollutants, and NO2 is commonly included in air quality objectives and regulations. NOx levels also affect the production of the nitrate component of secondary aerosol particles and other pollutants, such as the lachrymator peroxyacetyl nitrate (PAN). The accurate measurement of NO and NO2 is therefore crucial for air quality monitoring and understanding atmospheric composition. The most commonly used approach for the measurement of NO is the chemiluminescent detection of electronically excited NO2 (NO∗2) formed from the NO + O3 reaction within the NOx analyser. Alkenes, ubiquitous in the atmosphere from biogenic and anthropogenic sources, also react with ozone to produce chemiluminescence and thus may contribute to the measured NOx signal. Their ozonolysis reaction may also be sufficiently rapid that their abundance in conventional instrument background cycles, which also utilises the reaction with ozone, differs from that in the measurement cycle such that the background subtraction is incomplete, and an interference effect results. This interference has been noted previously, and indeed, the effect has been used to measure both alkenes and ozone in the atmosphere. Here we report the results of a systematic investigation of the response of a selection of commercial NOx monitors to a series of alkenes. These NOx monitors range from systems used for routine air quality monitoring to atmospheric research instrumentation. The species-investigated range was from short-chain alkenes, such as ethene, to the biogenic monoterpenes. Experiments were performed in the European PHOtoREactor (EUPHORE) to ensure common calibration and samples for the monitors and to unequivocally confirm the alkene levels present (via Fourier transform infrared spectroscopy - FTIR). The instrument interference responses ranged from negligible levels up to 11 %, depending upon the alkene present and conditions used (e.g. the presence of co-reactants and differing humidity). Such interferences may be of substantial importance for the interpretation of ambient NOx data, particularly for high VOC, low NOx environments such as forests or indoor environments where alkene abundance from personal care and cleaning products may be significant

Review of low-cost sensors for indoor air quality: Features and applications

Humans spend the majority of their time indoors, where they are potentially exposed to hazardous pollutants. Within this context, over the past few years, there has been an upsurge of low-cost sensors (LCS) for the measurement of indoor air pollutants, motivated both by recent technological advances and by increased awareness of indoor air quality (IAQ) and its potential negative health impacts. Although not meeting the performance requirements for reference regulatory-equivalent monitoring indoors, LCS can provide informative measurements, offering an opportunity for high-resolution monitoring, emission source identification, exposure mitigation and managing IAQ and energy efficiency, among others. This article discusses the strengths and limitations that LCS offer for applications in the field of IAQ monitoring; it provides an overview of existing sensor technologies and gives recommendations for different indoor applications, considering their performance in the complex indoor environment and discussing future trends

Gas-phase and particulate products from the atmospheric degradation of the organothiophosphorus insecticide chlorpyrifos-methyl

The phosphorothioate structure is highly present in several organophosphorus pesticides. However, there is insufficient information about its degradation process after the release to the atmosphere and the secondary pollutants formed. Herein, the atmospheric reaction of chlorpyrifos-methyl (o,o-dimethyl o-(3,5,6-trichloropyridin-2-yl) phosphorothioate), is described for semi-urban or rural locations. The photo-oxidation under low NOx conditions (5-55 ppbV) was reproduced in a large outdoor simulation chamber, observing a rapid degradation (lifetime<3.5 h). The formation of gaseous products and particulate matter (aerosol yield 2-8%) was monitored. The chemical composition of minor products (gaseous and particulate) was studied, identifying 15 multi-oxygenated derivatives. The most abundant products were ring-retaining molecules such as o,o-dimethyl o-(3,5,6-trichloropyridin-2-yl) phosphorothioate, dimethyl 3,5,6-trichloropyridin-2-yl phosphate, o-methyl o-(3,5,6-trichloropyridin-2-yl) hydrogen phosphorothioate, 3,5,6-trichloropyridin-2-yl dihydrogen phosphate, 3,5,6-trichloropyridin-2-ol, and 3,5,6-trichloropyridine-2,4-diol. An atmospheric degradation mechanism has been proposed based on an oxidation started with OH-nucleophilic attack to P=S bond. The results have been extrapolated to other organothiophosphorus molecules, such as malathion, parathion, diazinon and methidathion, among many others, to estimate their photo-oxidative degradation and the expected products.The authors wish to thank the EUPHORE staff and J.T.B. The authors wish to acknowledge Ministerio de Economia y Competitividad for IMPLACAVELES (CGL2013-49093-C2-1-R) and IMPESTAT (CGL2010-18474/CLI) projects, and Generalitat Valenciana for the DESESTRES- Prometeo II project. The Fundacion CEAM is partly supported by Generalitat Valenciana - Spain. EUPHORE instrumentation is partly funded by MINECO - Spain, through INNPLANTA Project: PCT-440000-2010-003 and the projects FEDER CEAM10-3E-1301 and CEAM10-3E-1302.Borrás García, EM.; Tortajada-Genaro, LA.; Ródenas, M.; Vera, T.; Coscollá, C.; Yusá, V.; Muñoz, A. (2015). Gas-phase and particulate products from the atmospheric degradation of the organothiophosphorus insecticide chlorpyrifos-methyl. Chemosphere. 138:888-894. https://doi.org/10.1016/j.chemosphere.2014.11.067S88889413

Assessment of COVID-19 Lockdown Impact on the Air Quality in Eastern Spain: PM and BTX in Urban, Suburban and Rural Sites Exposed to Different Emissions

In early 2020, the COVID-19 pandemic spread globally, and severe measures to control it were implemented. This study investigates the impact of the lockdown on the air quality of three provinces in the Valencia region, eastern Spain, in the years 2015&ndash;2020, focusing on particulate matter (PM). A thorough statistical analysis using different approaches is conducted. Hourly patterns are also assessed. In addition, the role of meteorological parameters on PM is explored. The results indicate an overall PM10 reduction of 16.5% when comparing the lockdown in 2020 and the 2015&ndash;2019 period, while PM2.5 increased by 3.1%. As expected, urban zones experienced higher reductions than suburban zones, which experienced a PM concentration increase. The impact of the drastic drops of benzene, toluene and xylene (77.4%, 58.0% and 61.8%, respectively) on the PM values observed in urban sites is discussed. Our study provides insights on the effect of activity changes over a wide region covering a variety of air quality stations, urban, suburban and rural, and different emission types. The results of this work are a valuable reference and suggest the need for considering different factors when establishing scientific air pollution control strategies

Assessment of COVID-19 Lockdown Impact on the Air Quality in Eastern Spain: PM and BTX in Urban, Suburban and Rural Sites Exposed to Different Emissions

In early 2020, the COVID-19 pandemic spread globally, and severe measures to control it were implemented. This study investigates the impact of the lockdown on the air quality of three provinces in the Valencia region, eastern Spain, in the years 2015–2020, focusing on particulate matter (PM). A thorough statistical analysis using different approaches is conducted. Hourly patterns are also assessed. In addition, the role of meteorological parameters on PM is explored. The results indicate an overall PM10 reduction of 16.5% when comparing the lockdown in 2020 and the 2015–2019 period, while PM2.5 increased by 3.1%. As expected, urban zones experienced higher reductions than suburban zones, which experienced a PM concentration increase. The impact of the drastic drops of benzene, toluene and xylene (77.4%, 58.0% and 61.8%, respectively) on the PM values observed in urban sites is discussed. Our study provides insights on the effect of activity changes over a wide region covering a variety of air quality stations, urban, suburban and rural, and different emission types. The results of this work are a valuable reference and suggest the need for considering different factors when establishing scientific air pollution control strategies

Gas-phase degradation of the herbicide ethalfluralin under atmospheric conditions

International audienceThe gas-phase degradation of ethalfluralin, N-ethyl-a,a,a-trifluoro-N-(2-methylallyl)-2,6-dinitro-p-toluidine,a widely used herbicide, was investigated under atmospheric conditions at the large outdoor Europeansimulation chamber (EUPHORE) in Valencia, Spain. The photolysis of ethalfluralin was investigatedunder solar radiation and the mean photolysis rate coefficient was determined: J(ethalfluralin)= (1.3 ± 0.2) 103 s1 (JNO2 = 8 103 s1). The rate coefficients for the reactions of hydroxyl radicalsand ozone with ethalfluralin in the dark were also measured under atmospheric conditions usingthe relative rate and the absolute rate technique, respectively. The rate coefficients values for the reactionsof kOH(ethalfluralin) = (3.5 ± 0.9) 1011 cm3 molecule1 s1, and kO3(ethalfluralin)= (1.6 ± 0.4) 1017 cm3 molecule1 s1 were determined at 300 ± 5 K and atmospheric pressure.The results show that removal of ethalfluralin from the atmosphere by reactions with OH radicals(s 4 h) or ozone (s 25 h) is slow compared to loss by photolysis. The available kinetic data suggestthat the gas-phase tropospheric degradation of ethalfluralin will be controlled mainly by photolysisand provide an estimate for the tropospheric lifetime of approximately 12 min. The atmospheric implicationsof using ethalfluralin as a herbicide are discussed

Studies on the atmospheric fate of propachlor (2-chloro-N-isopropylacetanilide) in the gas-phase

International audienceThe gas-phase degradation of propachlor (2-chloro-N-isopropylacetanilide), a widely used herbicide, was investigated under atmospheric conditions at the large outdoor European simulation chamber (EUPHORE) in Valencia, Spain. The rate coefficient for the reaction of hydroxyl radicals with propachlor was measured using a conventional relative rate technique. A value of the rate coefficient for the reaction of OH radicals with propachlor, kOH(propachlor) = (1.5 ± 0.3) × 10−11 cm3 molecule−1 s−1 was determined at 300 ± 5 K and atmospheric pressure. Rate coefficient data for the reaction of OH radicals with N,N-diisopropylaniline and N-methylacetanilide, which have structural similarities to propachlor, were also obtained using the relative rate method, kOH(N,N-diisopropylaniline) = (4.4 ± 0.5) × 10−11 cm3 molecule−1 s−1 and kOH(N-methylacetanilde) = (2.7 ± 0.2) × 10−11 cm3 molecule−1 s−1, respectively. The rate coefficients for photolysis of propachlor, J(propachlor) < 2.0 × 10−5 s−1, and reaction of ozone with propachlor, kO3kO3(propachlor) < 1.5 × 10−19 cm3 molecule−1 s−1, under atmospheric conditions were also determined. The available kinetic data suggest that the gas-phase tropospheric degradation of propachlor will be mainly controlled by reaction with OH and possibly NO3 radicals, and provide the basis of an estimate for the propachlor tropospheric lifetime of approximately 20 h. The atmospheric implications of the use of this species as a herbicide are discussed