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Zongbo Shi, my colleague, has collated and analysed data for a lot of cities around the world, for ozone, nitrogen oxides and particulate matter, during the lockdown period. Additionally, we didnd BC was most robustly associated with adverse health outcomes such as lung inammation, among different air pollution components, under a scenario of air pollution reduction during the Beijing Olympics. M. Rami Alfarra, William J. Bloss, Chak Chan, Ying Chen, Shahzad Gani, Yiqun Han, Roy M. Harrison, M. Anwar H. Khan, Saewung Kim, James Lee, Christian Pfrang, Ulrich P oschl, Zongbo Shi, Peter Styring, Dominik van Pinxteren, Timothy J. Wallington and Tong Zhu DOI: 10.1039/D1FD90012A Shahzad Gani opened discussion of the paper by Ying Chen: You hypothesize abouttheozone concentrationsincreasing astheNO x levelreduces. [Extracted from the article]

In contrast to the instability of (H 2 SO 4) 1 (NH 3) 1 clusters, the moderate evaporation of (H 2 SO 4) 1 (DMA) 1 1,2 indicates that H 2 SO 4 can form particles efficiently even with a low DMA concentration (e.g., <5 ppt). Because a negatively charged [(HSO 4) 1 (NH 3) 1 ] cluster is more stable than a neutral (H 2 SO 4) 1 (NH 3) 1 cluster, H 2 SO 4 -NH 3 nucleation usually occurs via the ion-induced mechanism. 3 Aer this correction, the rates for this experiment are consistent with a kinetic model, indicating that sulfuric acid-dimethylamine nucleation occurs at the kinetic limit under a high dimethylamine concentration. Previous laboratory studies that reported the dependency of the nucleation rate on the dimethylamine (DMA) concentrationatlowDMAconcentrationsindicateamoderateevaporationrate. [Extracted from the article]

Sources identied include gas-phase reactions, heterogeneous processes (dark and photo-enhanced, on ground and aerosol surfaces), combustion emissions (road traffic, biomass burning, wildres),biogenic sources(soil bacteria,biocrusts), potential ocean surface sources, andcondensedphasephotolysis (e.g.ofnitrate aerosol). Adam Milsom returned to the discussion of the paper by Guo Li by communicating: The phase state of an aerosol can affect key aerosol multiphase processes such as chemical reaction and water uptake. Danah Alshammari, William Bloss, Ying Chen, Judith C. Chow, Shahzad Gani, Roy Harrison, Dawei Hu, Guo Li, Gordon McFiggans, Adam Milsom, Andrea M. Oyarz ' un Aravena, Christian Pfrang, Zongbo Shi, Deepchandra Srivastava, Peter Styring, Hang Su, John G. Watson and Jingsha Xu DOI: 10.1039/D1FD90015C Ying Chen opened the discussion of the paper by Guo Li: I have a question regardingyouroutdoorchamber. For the inorganic particles, the aerosol concentrations are estimated by the anion concentrations, in equilibrium with the measured NH 3 (g). [Extracted from the article]

Discussions FaradayDiscussions This journal is © The Royal Society of Chemistry 2021 Faraday Discuss.,2021, 226,191-206 | 203 Sue Grimmond continued the discussion of the paper by Jessica Slater: In a follow-up to other questions asked in this session. Letmeprefacethatbysayingthatinthe UK, in the summer at the time of therst lockdown, we saw huge reductions in FaradayDiscussions Discussions 192 | Faraday Discuss.,2021, 226,191-206 This journal is © The Royal Society of Chemistry 2021 NO 2, mostly as a result of diesel traffic volumes falling. Sue Grimmond answered: Tall buildings profoundly affect circulation both betweenthebuildings(i.e.,theurbancanopylayer,UCLinFig.1inourpaper)and FaradayDiscussions Discussions 196 | Faraday Discuss.,2021, 226,191-206 This journal is © The Royal Society of Chemistry 2021 forsomedistanceabovebuildings(i.e.theroughnesssub-layer,RSL,Fig.1inour paper). FaradayDiscussions Discussions 194 | Faraday Discuss.,2021, 226,191-206 This journal is © The Royal Society of Chemistry 2021 Deepchandra Srivastava asked Jian Zhen Yu and Peter Brimblecombe: From the source apportionment studies performed during lockdown, it is evident that thereisasignicantreductionintheprimaryspeciesconcentration,butopposite tothis,anincreasehasbeenobservedforthesecondaryfractions. [Extracted from the article]

Timothy Wallington responded: As tailpipe PM emissions have decreased, non-exhaust PM emissions have become relatively more important. Therefore, in thenextve years,electrical vehicle adoption might causeadrastic increase in the contribution of these emissions (i.e., non-exhaust emissions) to the OC mass which may counterbalance the signican't reduction of tailpipe contribution that was achieved during the same period. Abdulmalik H. Altuwayjiri, William J. Bloss, Roy M. Harrison, Lyudmila Mihaylova, Luisa T. Molina, Andrea M. Oyarz ' un Aravena, Christian Pfrang, Jamie Schauer, Jessica Slater, Deepchandra Srivastava, Peter Styring, Timothy J. Wallington, Peng Wang and John G. Watson DOI: 10.1039/D1FD90013G Christian Pfrang opened discussion of the introductory lecture by Luisa Molina by communicating: Many thanks for your excellent introductory lecture (DOI: 10.1039/d0fd00123f). Although the restrictions were not directly targeting local ambient emissions, numerous studies have reported a signican't reductioninPM 2.5 aswellasgaseouspollutantlevels(e.g.,carbonmonoxide(CO), nitrogen oxides (NO x), and benzene (C 6 H 6)), during the COVID-19 pandemic across polluted cities (e.g., New York, Milan, and Beijing), due to the drastic decline in anthropogenic emissions. [Extracted from the article]

Wintertime urban air pollution in many global megacities is characterised by episodic rapid increase in particulate matter concentrations associated with elevated relative humidity – so-called haze episodes, which have become characteristic of cities such as Beijing. Atmospheric chemistry within haze combines gas- and condensed-phase chemical processes, leading to the growth in secondary species such as sulphate aerosols. Here, we integrate observations of reactive gas phase species (HONO, OH, NOx) and time-resolved aerosol composition, to explore observational constraints on the mechanisms responsible for sulphate growth during the onset of haze events. We show that HONO abundance is dominated by established fast gas-phase photochemistry, but the consideration of the additional formation potentially associated with condensed-phase oxidation of S species by aqueous NO2 leading to NO2− production and hence HONO release, improves agreement between observed and calculated gas-phase HONO levels. This conclusion is highly dependent upon aerosol pH, ionic strength and particularly the parameterisation employed for S(IV) oxidation kinetics, for which an upper limit is derived. [ABSTRACT FROM AUTHOR]

The article discusses a discussion offering views of several chemists in 2016 Faraday Discussions meeting of Great Britain's Royal Society of Chemistry on topics including chemical complexity of the urban atmosphere, less reactive molecule with ozone, and general products of chemical reactions.

The article discusses a discussion offering views of several chemists in 2016 Faraday Discussions meeting of Great Britain's Royal Society of Chemistry on topics including importance of emissions from the cooking sector and residential heating, wood combustion and primary osteoarthritis.

The article discusses a discussion offering views of several chemists in 2016 Faraday Discussions meeting of Great Britain's Royal Society of Chemistry on topics including timescales of mixing and of chemistry, nitrogen oxide levels, and chemiluminescence.

A substantial body of recent literature has shown that boundary layer HONO levels are higher than can be explained by simple, established gas-phase chemistry, to an extent that implies that additional HONO sources represent a major, or the dominant, precursor to OH radicals in such environments. This conclusion may be reached by analysis of point observations of (for example) OH, NO and HONO, alongside photochemical parameters; however both NO and HONO have non-negligible atmospheric lifetimes, so these approaches may be problematic if substantial spatial heterogeneity exists. We report a new dataset of HONO, NOx and HOx observations recorded at an urban background location, which support the existence of additional HONO sources as determined elsewhere. We qualitatively evaluate the possible impacts of local heterogeneity using a series of idealised numerical model simulations, building upon the work of Lee et al. (J. Geophys. Res., 2013, DOI: 10.1002/2013JD020341). The simulations illustrate the time required for photostationary state approaches to yield accurate results following substantial perturbations in the HOx/NOx/NOy chemistry, and the scope for bias to an inferred HONO source from NOx and VOC emissions in either a positive or negative sense, depending upon the air mass age following emission. To assess the extent to which these impacts may be present in actual measurements, we present exploratory spatially resolved measurements of HONO and NOx abundance obtained using a mobile instrumented laboratory. Measurements of the spatial variability of HONO in urban, suburban and rural environments show pronounced changes in abundance are found in proximity to major roads within urban areas, indicating that photo-stationary steady state (PSS) analyses in such areas are likely to be problematic. The measurements also show areas of very homogeneous HONO and NOx abundance in rural, and some suburban, regions, where the PSS approach is likely to be valid. Implications for future exploration of HONO production mechanisms are discussed. [ABSTRACT FROM AUTHOR]

The removal of SO2 in the presence of alkene–ozone systems has been studied for ethene, cis-but-2-ene, trans-but-2-ene and 2,3-dimethyl-but-2-ene, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity for all four alkene–ozone systems confirming a significant reaction for stabilised Criegee intermediates (SCI) with H2O. The observed SO2 removal kinetics are consistent with relative rate constants, k(SCI + H2O)/k(SCI + SO2), of 3.3 (±1.1) × 10−5 for CH2OO, 26 (±10) × 10−5 for CH3CHOO derived from cis-but-2-ene, 33 (±10) × 10−5 for CH3CHOO derived from trans-but-2-ene, and 8.7 (±2.5) × 10−5 for (CH3)2COO derived from 2,3-dimethyl-but-2-ene. The relative rate constants for k(SCI decomposition)/k(SCI + SO2) are −2.3 (±3.5) × 1011 cm−3 for CH2OO, 13 (±43) × 1011 cm−3 for CH3CHOO derived from cis-but-2-ene, −14 (±31) × 1011 cm−3 for CH3CHOO derived from trans-but-2-ene and 63 (±14) × 1011 cm−3 for (CH3)2COO. Uncertainties are ±2σ and represent combined systematic and precision components. These values are derived following the approximation that a single SCI is present for each system; a more comprehensive interpretation, explicitly considering the differing reactivity for syn- and anti-SCI conformers, is also presented. This yields values of 3.5 (±3.1) × 10−4 for k(SCI + H2O)/k(SCI + SO2) of anti-CH3CHOO and 1.2 (±1.1) × 1013 for k(SCI decomposition)/k(SCI + SO2) of syn-CH3CHOO. The reaction of the water dimer with CH2OO is also considered, with a derived value for k(CH2OO + (H2O)2)/k(CH2OO + SO2) of 1.4 (±1.8) × 10−2. The observed SO2 removal rate constants, which technically represent upper limits, are consistent with decomposition being a significant, structure dependent, sink in the atmosphere for syn-SCI. [ABSTRACT FROM AUTHOR]

Formation of the NO3 radical was observed following photolysis of the CH2I2 + O2 system at 248 nm under ambient atmospheric boundary layer conditions (∼760 Torr and 297 K) in the presence of NO2. The Criegee intermediate (CI) CH2OO is believed to be responsible for the NO3 production. The potential of such reactions to enhance the rate of NO3 production in the atmosphere is discussed. [ABSTRACT FROM AUTHOR]

The gas-phase reactions of ozone with alkenes can be significant sources of free radicals (OH, HO2and RO2) in the Earth''s atmosphere. In this study the total radical production and degradation products from ethene ozonolysis have been measured, under conditions relevant to the troposphere, during a series of detailed simulation chamber experiments. Experiments were carried out in the European photoreactor EUPHORE (Valencia, Spain), utilising various instrumentation including a chemical-ionisation-reaction time-of-flight mass-spectrometer (CIR-TOF-MS) measuring volatile organic compounds/oxygenated volatile organic compounds (VOCs/OVOCs), a laser induced fluorescence (LIF) system for measuring HO2radical products and a peroxy radical chemical amplification (PERCA) instrument measuring HO2+ ΣRO2. The ethene + ozone reaction system was investigated with and without an OH radical scavenger, in order to suppress side reactions. Radical concentrations were measured under dry and humid conditions and interpreted through detailed chemical chamber box modelling, incorporating the Master Chemical Mechanism (MCMv3.1) degradation scheme for ethene, which was updated to include a more explicit representation of the ethene–ozone reaction mechanism.The rate coefficient for the ethene + ozone reaction was measured to be (1.45 ± 0.25) × 10−18cm3molecules−1s−1at 298 K, and a stabilised Criegee intermediate yield of 0.54 ± 0.12 was determined from excess CO scavenger experiments. An OH radical yield of 0.17 ± 0.09 was determined using a cyclohexane scavenger approach, by monitoring the formation of the OH-initiated cyclohexane oxidation products and HO2. The results highlight the importance of knowing the [HO2] (particularly under alkene limited conditions and high [O3]) and scavenger chemistry when deriving radical yields. An averaged HO2yield of 0.27 ± 0.07 was determined by LIF/model fitting. The observed yields are interpreted in terms of branching ratios for each channel within the postulated ethene ozonolysis mechanism. [ABSTRACT FROM AUTHOR]

The removal of SO2 in the presence of alkene-ozone systems has been studied for ethene, cis-but-2-ene, trans-but-2-ene and 2,3-dimethyl-but-2-ene, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity for all four alkene-ozone systems confirming a significant reaction for stabilised Criegee intermediates (SCI) with H2O. The observed SO2 removal kinetics are consistent with relative rate constants, k(SCI + H2O)/k(SCI + SO2), of 3.3 (±1.1) × 10(-5) for CH2OO, 26 (±10) × 10(-5) for CH3CHOO derived from cis-but-2-ene, 33 (±10) × 10(-5) for CH3CHOO derived from trans-but-2-ene, and 8.7 (±2.5) × 10(-5) for (CH3)2COO derived from 2,3-dimethyl-but-2-ene. The relative rate constants for k(SCI decomposition)/k(SCI + SO2) are -2.3 (±3.5) × 10(11) cm(-3) for CH2OO, 13 (±43) × 10(11) cm(-3) for CH3CHOO derived from cis-but-2-ene, -14 (±31) × 10(11) cm(-3) for CH3CHOO derived from trans-but-2-ene and 63 (±14) × 10(11) cm(-3) for (CH3)2COO. Uncertainties are ±2σ and represent combined systematic and precision components. These values are derived following the approximation that a single SCI is present for each system; a more comprehensive interpretation, explicitly considering the differing reactivity for syn- and anti-SCI conformers, is also presented. This yields values of 3.5 (±3.1) × 10(-4) for k(SCI + H2O)/k(SCI + SO2) of anti-CH3CHOO and 1.2 (±1.1) × 10(13) for k(SCI decomposition)/k(SCI + SO2) of syn-CH3CHOO. The reaction of the water dimer with CH2OO is also considered, with a derived value for k(CH2OO + (H2O)2)/k(CH2OO + SO2) of 1.4 (±1.8) × 10(-2). The observed SO2 removal rate constants, which technically represent upper limits, are consistent with decomposition being a significant, structure dependent, sink in the atmosphere for syn-SCI.

Formation of the NO3 radical was observed following photolysis of the CH2I2 + O2 system at 248 nm under ambient atmospheric boundary layer conditions (~760 Torr and 297 K) in the presence of NO2. The Criegee intermediate (CI) CH2OO is believed to be responsible for the NO3 production. The potential of such reactions to enhance the rate of NO3 production in the atmosphere is discussed.

A tuneable, high pulse-repetition-frequency, solid state Nd:YAG pumped titanium sapphire laser capable of generating radiation for the detection of OH, HO2, NO and IO radicals in the atmosphere by laser induced fluorescence (LIF) has been developed. The integration of the laser system operating at 308 nm into a field measurement apparatus for the simultaneous detection of hydroxyl and hydroperoxy radicals is described, with detection limits of 3.1 x 10(5) molecule cm(-3) (0.012 pptv in the boundary layer) and 2.6 x 10(6) molecule cm(-3) (0.09 pptv) achieved for OH and HO2 respectively (30 s signal integration, 30 s background integration, signal-to-noise ratio = 1). The system has been field tested and offers several advantages over copper vapour laser pumped dye laser systems for the detection of atmospheric OH and HO2 radicals by LIF, with benefits of greater tuning range and ease of use coupled with reduced power consumption, instrument footprint and warm-up time. NO has been detected in the atmosphere at approximately 1 ppbv by single photon LIF using the Alpha 2Sigma+ <-- Chi 2Pi1/2 (0,0) transition at 226 nm, with absolute concentrations in good agreement with simultaneous measurements made using a chemiluminescence analyser. With some improvements in performance, particularly with regard to laser power, the theoretical detection limit for NO is projected to be approximately 2 x 10(6) molecule cm(-3) (0.08 pptv). Whilst operating at 445 nm, the laser system has been used to readily detect the IO radical in the laboratory, and although it is difficult to project the sensitivity in the field, an estimate of the detection limit is < 1 x 10(5) molecule cm(-3) (< 0.004 pptv), well below previously measured atmospheric concentrations of IO.