Domestic cooking is a source of indoor air pollutants, including volatile organic compounds (VOCs), which can impact on indoor air quality. However, the real-time VOC emissions from cooking are not well characterised, and similarly, the resulting secondary chemistry is poorly understood. Here, selected-ion flow-tube mass spectrometry (SIFT-MS) was used to monitor the real-time VOC emissions during the cooking of a scripted chicken and vegetable stir-fry meal, in a room scale, semi-realistic environment. The VOC emissions were dominated by alcohols (70% of total emission), but also contained a range of aldehydes (14%) and terpenes (5%), largely attributable to the heating of oil and the preparation and heating of spices, respectively. The direct cooking-related VOC emissions were then simulated using the Indoor Chemical Model in Python (INCHEM-Py), to investigate the resulting secondary chemistry. Modelling revealed that VOC concentrations were dominated by direct emissions, with only a small contribution from secondary products, though the secondary species were longer lived than the directly emitted species. Following cooking, hydroxyl radical concentrations reduced by 86%, while organic peroxy radical levels increased by over 700%, later forming secondary organic nitrates, peroxyacylnitrates (PANs) and formaldehyde. Monoterpene emissions were shown to drive the formation of secondary formaldehyde, albeit to produce relatively modest concentrations (average of 60 ppt). Sensitivity analysis of the simulation conditions revealed that increasing the outdoor concentrations of ozone and NOx species (2.9× and 9×, respectively) resulted in the greatest increase in secondary product formation indoors (≈400%, 200% and 600% increase in organic nitrates, PANs and formaldehyde production, respectively). Given the fact that climate change is likely to result in increased ozone concentrations in the future, and that increased window-opening in response to rising temperatures is also likely, higher concentrations of indoor oxidants are likely in homes in the future. This work, therefore, suggests that cooking could be a more important source of secondary pollutants indoors in the future.

Indoor AirVolume 30, Issue 3 p. 373-376 EDITORIALFree Access The past, present, and future of indoor air chemistry Gabriel Bekö, Corresponding Author Gabriel Bekö gab@byg.dtu.dk orcid.org/0000-0001-6107-8336 International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark Correspondence Gabriel Bekö, Technical University of Denmark, Nils Koppels Allé 402, 2800 Kgs. Lyngby, Denmark. Email: gab@byg.dtu.dkSearch for more papers by this authorNicola Carslaw, Nicola Carslaw orcid.org/0000-0002-5290-4779 Department of Environment and Geography, University of York, York, UKSearch for more papers by this authorPatrik Fauser, Patrik Fauser Department of Environmental Science, Århus University, Roskilde, DenmarkSearch for more papers by this authorVioleta Kauneliene, Violeta Kauneliene Faculty of Chemical Technology, Kaunas University of Technology, Kaunas, LithuaniaSearch for more papers by this authorSascha Nehr, Sascha Nehr European University of Applied Sciences, Brühl, GermanySearch for more papers by this authorGavin Phillips, Gavin Phillips Faculty of Science and Engineering, University of Chester, Chester, UKSearch for more papers by this authorDikaia Saraga, Dikaia Saraga National Center for Scientific Research "Demokritos", Athens, GreeceSearch for more papers by this authorCoralie Schoemaecker, Coralie Schoemaecker orcid.org/0000-0001-7016-9432 Physicochimie des Processus de Combustion et de l’Atmosphère, Université Lille, Lille, FranceSearch for more papers by this authorAneta Wierzbicka, Aneta Wierzbicka Devision of Ergonomics and Aerosol Technology, Lund University, Lund, SwedenSearch for more papers by this authorXavier Querol, Xavier Querol Institute of Environmental Assessment and Water Research, Barcelona, SpainSearch for more papers by this author Gabriel Bekö, Corresponding Author Gabriel Bekö gab@byg.dtu.dk orcid.org/0000-0001-6107-8336 International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark Correspondence Gabriel Bekö, Technical University of Denmark, Nils Koppels Allé 402, 2800 Kgs. Lyngby, Denmark. Email: gab@byg.dtu.dkSearch for more papers by this authorNicola Carslaw, Nicola Carslaw orcid.org/0000-0002-5290-4779 Department of Environment and Geography, University of York, York, UKSearch for more papers by this authorPatrik Fauser, Patrik Fauser Department of Environmental Science, Århus University, Roskilde, DenmarkSearch for more papers by this authorVioleta Kauneliene, Violeta Kauneliene Faculty of Chemical Technology, Kaunas University of Technology, Kaunas, LithuaniaSearch for more papers by this authorSascha Nehr, Sascha Nehr European University of Applied Sciences, Brühl, GermanySearch for more papers by this authorGavin Phillips, Gavin Phillips Faculty of Science and Engineering, University of Chester, Chester, UKSearch for more papers by this authorDikaia Saraga, Dikaia Saraga National Center for Scientific Research "Demokritos", Athens, GreeceSearch for more papers by this authorCoralie Schoemaecker, Coralie Schoemaecker orcid.org/0000-0001-7016-9432 Physicochimie des Processus de Combustion et de l’Atmosphère, Université Lille, Lille, FranceSearch for more papers by this authorAneta Wierzbicka, Aneta Wierzbicka Devision of Ergonomics and Aerosol Technology, Lund University, Lund, SwedenSearch for more papers by this authorXavier Querol, Xavier Querol Institute of Environmental Assessment and Water Research, Barcelona, SpainSearch for more papers by this author First published: 25 April 2020 https://doi.org/10.1111/ina.12634AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat “In developed countries, we spend 80%-90% of our time indoors” is the opening sentence for most grant applications and publications in our field. But has this well-worn truism lost its impact? We know that the majority of our exposure to air pollution occurs indoors, so why has indoor air quality not received the attention it deserves and how do we as a community better communicate this message? Recently, there has been increasing interest from experts from a wide range of backgrounds, including outdoor air quality scientists. They have enhanced our community, sparking a rapid evolution in the measurement technology used indoors, and the number, diversity, and novelty of findings. The INDoor AIR POLLution NETwork (INDAIRPOLLNET) was recently supported by the European Cooperation in Science and Technology (COST), following submission of a proposal that began with the sentence highlighted above. It consists of ~200 participants from 38 countries, comprising both scientists and practitioners in chemistry, biology, aerosol characterization, toxicology, exposure, emissions and chemical risk assessments, material design, building physics, civil engineering, and standardization. Over a four-year period, INDAIRPOLLNET will address the current state of indoor air pollution, with emphasis on indoor air chemistry (IAC), including the associated research needs, challenges, and ways to address them. A liaison with the International Organization for Standardization (ISO) will facilitate the transfer of this scientific knowledge to practice. Increasing climate change awareness is driving rigorous energy efficiency measures with buildings becoming more airtight, though adverse health effects can be associated with lower ventilation rates.1 Air pollutant concentrations are often higher indoors than outdoors, particularly following activities such as cleaning, cooking, and smoking.2 More than two million healthy life years are lost across Europe because of indoor air pollution, including indoor exposure to outdoor pollutants, indoor combustion sources, moisture, and emissions from building materials and consumer products.3 There are vast differences in building types and uses, occupant behavior, geographic locations, ventilation systems, and indoor and outdoor sources. Chemical processes indoors and their relation to those occurring outdoors must be well-understood, in order to extrapolate results to a wider range of buildings and locations than in the relatively few, in which measurements have been made. In its first year, INDAIRPOLLNET used seven subgroups to mine recent literature to summarize what existing measurement and model studies reveal about IAC. The research priorities from the subgroups are now presented. 1 CHEMICAL TRANSFORMATIONS Indoor chemical processes have been identified by reviewing laboratory, field, and modeling studies both indoors and, where relevant, outdoors. The relative importance of chemical processes indoors differs to outdoors because of higher surface-to-volume ratios, and differences in pollutant sources and dispersion, light characteristics, and temperature and humidity profiles.4, 5 The following priorities were identified: Assess the potential for indoor chemistry in the gas-phase, with emphasis on the following: Role of photolysis (via attenuated solar and artificial light sources), Comparison of the relative importance of OH, Cl, NO3, and O3 as oxidants, the conditions where each dominates and routes to formation, Contribution of different reaction pathways to the formation of secondary products, and Competition between chemical reactions and ventilation rate. Advance knowledge on the abundance of organic trace constituents in indoor air and the identification of new constituents through total OH reactivity measurements compared with measurable individual trace gas measurements. Investigate the impact of solid- and liquid-phase processes indoors (eg, reactivity in the liquid-phase indoors, including acid–base chemistry). Parameterize heterogeneous processes (production yields of secondary species such as aldehydes and HONO) for representative indoor surfaces and in real environments. 2 BUILDING MATERIALS, HOUSEHOLD PRODUCTS, AND OCCUPANT BEHAVIOR Building and household products (eg, wood-based building materials, paints, varnishes, cleaning and personal care products, air fresheners, combustion appliances, electronic appliances, furniture, carpets, and toys) as well as occupant activities (eg, cooking, smoking, and cleaning) can contribute significantly to indoor air pollution. A comparison of 13 labeling schemes for construction products worldwide has identified 15 lists of target compounds, with 611 individual chemicals occurring on at least one of the lists.6 Indoor surfaces may act as both sources and sinks of gas-phase air pollutants; there is increasing interest in secondary pollutant emissions following surface interactions indoors.5, 7 The following are the identified research priorities: Improve the characterization of pollutant emissions, deposition, and chemical transformations on various indoor surfaces for the identification and development of building and furnishing materials for better indoor air quality. Design field studies with a particular focus on the role of semivolatile organic compounds (SVOCs) and their reaction products in surface chemistry and related health effects. Disentangle the role played by humidity (potential impact on aqueous chemistry) versus reactive species (eg, chlorine) in surface reactivity. Study the impact of building construction, location, and operation on IAC. 3 OCCUPANTS Humans emit a range of organic compounds from sweat and sebaceous secretions from skin, breath, and intestinal gases. The compounds associated with the presence of humans contribute 40%-57% of the volatile organic compound (VOC) concentrations indoors in daytime.8, 9 Studies on occupant-related chemical transformations have mainly focused on ozonolysis of squalene, a major skin oil constituent.10 The following research priorities were identified: Investigate the personal and environmental factors that influence human emissions (eg, diet, stress level, personal hygiene, age, sex, health condition, activity level, personal care products, clothing, and its laundering). Study the inter- and intrapersonal variability and the influence of prior exposure on human dermal and oral emissions and their reactive capacity. Perform real-time measurements of OH, NO3, Criegee intermediates, and other short-lived, highly reactive species in occupied and unoccupied indoor environments. Investigate the influence of occupancy on indoor surfaces as well as on the composition of airborne particles. 4 MICROBIAL ACTIVITY Microbial life is ubiquitous within buildings11 and is a frequent cause of indoor air quality problems and health effects.12 Microbial colonies such as molds produce a wide variety of VOCs through their metabolisms, which encompass a range of functional moieties.13 The behavior of analogous microbes in the ambient atmosphere suggests that their indoor counterparts are chemically and photochemically active and are likely to affect chemistries both in the gas-phase and on surfaces, including on aerosols. Future research priorities include the following: Determine the relative VOC load from microbial activity and the impact on IAC in an “ordinary dwelling” compared to a “problem dwelling” with similar occupancy. Determine the influence of species variety indoors and of the balance between the building biome and the occupant biome on indoor air chemistry. Investigate the levels of toxic volatile emissions resulting from microbial processing of widely used building materials. Coordinate a network of well-characterized test facilities with a minimum set of controlled variables in conjunction with a coupled indoor chemistry/dynamic model framework, in order to address the potential variability due to geographic differences in species, indoor environments, and emission factors. Individually study microbial activity by the use of standardized coupons whereby known quantities of microbes are introduced into well-characterized realistic environments and the marginal effects of the microbial activity are measured. 5 PARTICLES Airborne particles form an integral part of IAC, as dynamic changes between gas-phase and particle-phase take place continuously.14 Particles in indoor air are influenced by both physical and chemical processes, which change their physical characteristics, chemical composition, and concentrations.15 Recent studies based on real-time aerosol mass spectrometry have brought novel understanding of chemical transformations taking place indoors. Future studies are recommended in the following domains: Study the factors influencing SVOC uptake on particles (eg, chemical composition, number size distribution, surface area, and environmental parameters). Determine size-resolved particle- and gas-phase chemical emission factors and mass spectra/signatures for specific indoor sources under controlled laboratory settings with parallel use of proton-transfer-reaction mass spectrometry and aerosol mass spectrometry. Assess the oxidative reactivity of particles from specific sources and mixtures under laboratory conditions and compare with measurements in occupied real indoor environments. Study the change in physicochemical characteristics of particles upon infiltration and the transformations that occur when outdoor and indoor air pollutants in the gas- and particle-phase interact. 6 SOURCE APPORTIONMENT Receptor models apportion the measured mass of an atmospheric pollutant at a given site (receptor), to its emission sources by using multivariate analysis to solve a mass balance equation.16 Positive matrix factorization (PMF), chemical mass balance (CMB), and principal component analysis (PCA) are among the receptor models most frequently used. While the major sources of indoor air pollution have been identified, few studies have attempted to estimate the contribution of specific sources using such techniques, mainly because the presence of both indoor and outdoor sources, building-related mechanisms (eg, ventilation and infiltration), as well as outdoor meteorology and long-range transport of pollutants makes source apportionment challenging. Key research areas that warrant attention are as follows: The influence of IAC on source apportionment model applications, including the validity of assumptions and relevant constraints (eg, unstable source profiles over time). The dependence of receptor modeling applications on available decay rates, air exchange rates, and penetration factors. Improved estimates of the outdoor contribution in source apportionment of indoor pollutants. Perform source apportionment studies based on datasets obtained with real-time measurements with very short time resolution (eg, aerosol mass spectrometer and PTR-MS). Define basic guidelines for source apportionment in indoor environments and address reliability issues of online source apportionments based on low-cost sensor networks. 7 MODELING Indoor air pollutant measurement techniques are still unable to measure many pollutants at sufficient temporal frequency and with the required specificity in a wide enough range of buildings, to provide a broad and representative understanding of chemistry indoors. The development and use of indoor air models is, therefore, a substantial requirement for understanding IAC.17 Indoor air chemistry models need to include the important sources and sinks of pollutants within a building envelope, such as chemical reactions, material emissions and surface interactions, human activity, exchange of pollutants with outdoors, or transport of pollutants within/between different zones of a building. A number of challenges for modeling studies have been identified: Field experiments in real buildings, especially those with real-time measurements and real/simulated activities, are necessary to validate and improve models. Models often assume well-mixed air in buildings, when spatial variation within zones should be considered. Indoor air chemistry models typically use chemical mechanisms originally constructed for modeling outdoor chemistry and may lack appropriate degradation schemes. Current models typically include estimated photolysis rate indoors (although some measurements have become available recently18, 19) and often fail to consider the propagation of light from the windows throughout the indoor space. Modelers and experimentalists must work together; models help design experiments, and the experimental results can be used to improve models. The field of indoor air chemistry is moving forward rapidly, accelerated to a great extent by the Alfred P. Sloan Foundation's Chemistry of Indoor Environment program (whose Web site's homepage vividly flashes the “90%-sentence”). From the laboratory to the field, from test houses to climate chambers, and from extraordinary campaigns such as HOMEChem20 to modeling efforts such as the international MOCCIE consortium, invaluable data about indoor air chemistry and physics are being swiftly generated. Indoor air chemistry occupies an increasing share in the programs of the Indoor Air conference series and at meetings such as the recent joint conference of The International Societies of Exposure Science (ISES) and Indoor Air Quality and Climate (ISIAQ) in Kaunas, Lithuania. But as it often is the case in science, new answers generate new questions and we seem to have lots of them. Such new questions are to be welcomed. As Albert Einstein noted, “To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.” As we continue to address the unknowns of indoor air chemistry and allow our scientific curiosity to generate further insights, we should remember that we ultimately strive not only for understanding, but especially for healthier indoor environments. ACKNOWLEDGMENTS We thank those participants of INDAIRPOLLNET's Working Group 1, who actively contributed to the work, which resulted in this editorial. These participants are Elena Gomez Alvarez, Noel J. Aquilina, Steigvile Bycenkiene, Nuno Canha, Regina Duarte, Emer Duffy, Sebastien Dusanter, Renata Kovacevic, Mila Ródenas García, Pawel Misztal, Aleksandar Petrovski, Ana Maria Scutaru, Milena Jovasevic-Stojanovic, Kristina Plauškaitė-Šukienė, Teresa Vera, and Lenka Wimmerová. The authors gratefully acknowledge the support of the European Cooperation in Science and Technology (COST). REFERENCES 1Sundell J, Levin H, Nazaroff WW, et al. Ventilation rates and health: multidisciplinary review of the scientific literature. Indoor Air. 2011; 21: 191- 204. 2Nazaroff WW, Goldstein AH. Indoor chemistry: research opportunities and challenges. Indoor Air. 2015; 25: 357- 361. 3de Oliveira FE, Jantunen M, Carrer P, Seppänen O, Harrison P, Kephalopoulos S. EnVIE, Coordination action on indoor air quality and health effects. Final activity report; 2009. https://paginas.fe.up.pt/~envie/finalreports.html. Accessed October 22, 2019. 4Nehr S, Hosen E, Tanabe S-I. Emerging developments in the standardized chemical characterization of indoor air quality. Environ Int. 2017; 98: 233- 237. 5Weschler CJ, Carslaw N. Indoor chemistry. Environ Sci Technol. 2018; 52: 2419- 2428. 6Brown VM, Crump DR, Harrison PTC. Assessing and controlling risks from the emission of organic chemicals from construction products into indoor environments. Environ Sci Process Impacts. 2013; 15(12): 2164- 2171. 7Kruza M, Lewis AC, Morrison GC, Carslaw N. Impact of surface ozone interactions on indoor air chemistry: a modeling study. Indoor Air. 2017; 27: 1001- 1011. 8Liu S, Li R, Wild RJ, et al. Contribution of human-related sources to indoor volatile organic compounds in a university classroom. Indoor Air. 2016; 26: 925- 938. 9Tang X, Misztal PK, Nazaroff WW, Goldstein AH. Volatile organic compound emissions from humans indoors. Environ Sci Technol. 2016; 50: 12686- 12694. 10Weschler CJ. Roles of the human occupant in indoor chemistry. Indoor Air. 2016; 26: 6- 24. 11Kelley ST, Gilbert JA. Studying the microbiology of the indoor environment. Genome Biol. 2013; 14(2): 1- 9. 12Claeson AS, Nordin S, Sunesson A-L. Effects on perceived air quality and symptoms of exposure to microbially produced metabolites and compounds emitted from damp building materials. Indoor Air. 2009; 19(2): 102- 112. 13Misztal PK, Lymperopoulou DS, Adams RI, et al. Emission factors of microbial volatile organic compounds from environmental bacteria and fungi. Environ Sci Technol. 2018; 52(15): 8272- 8282. 14Lucattini L, Poma G, Covaci A, de Boer J, Lamoree MH, Leonards PEG. A review of semi-volatile organic compounds (SVOCs) in the indoor environment: occurrence in consumer products, indoor air and dust. Chemosphere. 2018; 201: 466- 482. 15Morawska L, Afshari A, Bae GN, et al. Indoor aerosols: from personal exposure to risk assessment – review. Indoor Air. 2013; 23: 462- 487. 16Belis CA, Larsen BR, Amato F, et al. European guide on air pollution source apportionment with receptor models. European Commission, Joint Research Centre, Institute for Environment and Sustainability. ISBN: 978-92-79-32513-7; 2014. http://dx.publications.europa.eu/10.2788/9307. Accessed October 22, 2019. 17Morrison GC, Carslaw N, Waring M. A modelling enterprise for chemistry of indoor environments (CIE). Indoor Air. 2017; 27: 1033- 1038. 18Kowal SF, Allen SR, Kahan TF. Wavelength-resolved photon fluxes of indoor light sources: Implications for HOx production. Environ Sci Technol. 2017; 51: 10423- 10430. 19Blocquet M, Guo F, Mendez M, et al. Impact of the spectral and spatial properties of natural light on indoor gas-phase chemistry: experimental and modeling study. Indoor Air. 2018; 28(3): 426- 440. 20Farmer DK, Vance ME, Abbatt JPD, et al. Overview of HOMEChem: house observations of microbial and environmental chemistry. Environ Sci Process Impacts. 2019; 21: 1280- 1300. Volume30, Issue3May 2020Pages 373-376 ReferencesRelatedInformation

We present a chemical ionization quadrupole mass spectrometer (CI-QMS) with a radio-frequency (RF) discharge ion source through N2∕CH3I as a source of primary ions. In addition to the expected detection of PAN, peracetic acid (PAA) and ClNO2 through well-established ion–molecule reactions with I− and its water cluster, the instrument is also sensitive to SO2, HCl and acetic acid (CH3C(O)OH) through additional ion chemistry unique to our ion source. We present ionization schemes for detection of SO2, HCl and acetic acid along with illustrative datasets from three different field campaigns underlining the potential of the CI-QMS with an RF discharge ion source as an alternative to 210Po. The additional sensitivity to SO2 and HCl makes the CI-QMS suitable for investigating the role of sulfur and chlorine chemistry in the polluted marine and coastal boundary layer.

Unlike many oxidised atmospheric trace gases, which have numerous production pathways, peroxyacetic acid (PAA) and PAN are formed almost exclusively in gas-phase reactions involving the hydroperoxy radical (HO2), the acetyl peroxy radical (CH3C(O)O2) and NO2 and are not believed to be directly emitted in significant amounts by vegetation. As the self-reaction of HO2 is the main photochemical route to hydrogen peroxide (H2O2), simultaneous observation of PAA, PAN and H2O2 can provide insight into the HO2 budget. We present an analysis of observations taken during a summertime campaign in a boreal forest that, in addition to natural conditions, was temporarily impacted by two biomass-burning plumes. The observations were analysed using an expression based on a steady-state assumption using relative PAA-to-PAN mixing ratios to derive HO2 concentrations. The steady-state approach generated HO2 concentrations that were generally in reasonable agreement with measurements but sometimes overestimated those observed by factors of 2 or more. We also used a chemically simple, constrained box model to analyse the formation and reaction of radicals that define the observed mixing ratios of PAA and H2O2. After nudging the simulation towards observations by adding extra, photochemical sources of HO2 and CH3C(O)O2, the box model replicated the observations of PAA, H2O2, ROOH and OH throughout the campaign, including the biomass-burning-influenced episodes during which significantly higher levels of many oxidized trace gases were observed. A dominant fraction of CH3O2 radical generation was found to arise via reactions of the CH3C(O)O2 radical. The model indicates that organic peroxy radicals were present at night in high concentrations that sometimes exceeded those predicted for daytime, and initially divergent measured and modelled HO2 concentrations and daily concentration profiles are reconciled when organic peroxy radicals are detected (as HO2) at an efficiency of 35 %. Organic peroxy radicals are found to play an important role in the recycling of OH radicals subsequent to their loss via reactions with volatile organic compounds.

The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX-2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe.The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx, hydrocarbons, peroxides, and other major HOx (OH + HO2) sources and sinks in a low-NOx environment (< 100 pptv of NO). The model simulations for OH agreed to within 10 % with in situ OH observations. Model simulations for HO2 agreed to within 17 % of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38 % at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpene-generated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans.

SupplementFigure S1.Photo: N2 emission observed between and around the pointed tungsten tips of the electrodes of the RF discharge source.Right: The emission spectrum was recorded with an Ocean-Optics USB-4000 spectrometer with optical fibre at various high-voltages.The strongest features (not fully resolved using the low-resolution (  1.5 nm) spectrograph) can be assigned to transitions from the ground vibrational level of the electronically excited N2 (C 3 u) state to the B 3 g state.

We analysed the extensive dataset from the HUMPPA-COPEC 2010 and the HOPE 2012 field campaigns in the boreal forest and rural environments of Finland and Germany, respectively, and estimated the abundance of stabilised Criegee intermediates (SCIs) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the aforementioned campaigns is caused at least partially by SCIs. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. Just like SCIs, the background OH concentration can be removed through the addition of sulfur dioxide. SCIs also add to the previously underestimated production rate of sulfuric acid. An average estimate of the SCI concentration of ∼ 5.0 × 104 molecules cm−3 (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCIs, though, over the boreal forest, significant for the conversion of SO2 into H2SO4. The large uncertainties in these calculations, owing to the many unknowns in the chemistry of Criegee intermediates, emphasise the need to better understand these processes and their potential effect on the self-cleaning capacity of the atmosphere.

During the summertime CYPHEX campaign (CYprus PHotochemical EXperiment 2014) in the eastern Mediterranean, multiple volatile organic compounds (VOCs) were measured from a 650 m hilltop site in western Cyprus (34° 57′ N/32° 23′ E). Periodic shifts in the northerly Etesian winds resulted in the site being alternately impacted by photochemically processed emissions from western (Spain, France, Italy) and eastern (Turkey, Greece) Europe. Furthermore, the site was situated within the residual layer/free troposphere during some nights which were characterized by high ozone and low relative humidity levels. In this study we examine the temporal variation of VOCs at the site. The sparse Mediterranean scrub vegetation generated diel cycles in the reactive biogenic hydrocarbon isoprene, from very low values at night to a diurnal median level of 80–100 pptv. In contrast, the oxygenated volatile organic compounds (OVOCs) methanol and acetone exhibited weak diel cycles and were approximately an order of magnitude higher in mixing ratio (ca. 2.5–3 ppbv median level by day, range: ca. 1–8 ppbv) than the locally emitted isoprene and aromatic compounds such as benzene and toluene. Acetic acid was present at mixing ratios between 0.05 and 4 ppbv with a median level of ca. 1.2 ppbv during the daytime. When data points directly affected by the residual layer/free troposphere were excluded, the acid followed a pronounced diel cycle, which was influenced by various local effects including photochemical production and loss, direct emission, dry deposition and scavenging from advecting air in fog banks. The Lagrangian model FLEXPART was used to determine transport patterns and photochemical processing times (between 12 h and several days) of air masses originating from eastern and western Europe. Ozone and many OVOC levels were ∼ 20 and ∼ 30–60 % higher, respectively, in air arriving from the east. Using the FLEXPART calculated transport time, the contribution of photochemical processing, sea surface contact and dilution was estimated. Methanol and acetone decreased with residence time in the marine boundary layer (MBL) with loss rate constants of 0.74 and 0.53 day−1 from eastern Europe and 0.70 and 0.34 day−1 from western Europe, respectively. Simulations using the EMAC model underestimate these loss rates. The missing sink in the calculation is most probably an oceanic uptake enhanced by microbial consumption of methanol and acetone, although the temporal and spatial variability in the source strength on the continents might play a role as well. Correlations between acetone and methanol were weaker in western air masses (r2 = 0.68), but were stronger in air masses measured after the shorter transport time from the east (r2 = 0.73).

The paper describes a study involving field measurements of nitrogen oxides and atmospheric particulate matter, and analysis aimed at estimating the uptake coefficient (gamma) and yield of nitryl chloride (f) in the heterogeneous processing of dinitrogen pentoxide in the reaction: N2O5 + Cl= ClNO2 + NO3-. The measurement site is at 800m altitude in a rural location in Western Germany, which is influenced by pollution from the adjacent Rhein-Main conurbation, and by long range transport of air of marine origin containing sea salt aerosol. This is the latest of several papers appearing in the literature reporting estimates of N2O5 uptake coefficients and reaction paths on ambient atmospheric aerosol of more or less defined composition. It is known from lab-

We present an estimation of the uptake coefficient (γ) and yield of nitryl chloride (ClNO2) (f) for the heterogeneous processing of dinitrogen pentoxide (N2O5) using simultaneous measurements of particle and trace gas composition at a semi-rural, non-coastal, mountain site in the summer of 2011. The yield of ClNO2 varied between (0.035 ± 0.027) and (1.38 ± 0.60) with a campaign average of (0.49 ± 0.35). The large variability in f reflects the highly variable chloride content of particles at the site. Uptake coefficients were also highly variable with minimum, maximum and average γ values of 0.004, 0.11 and 0.028 ± 0.029, respectively, with no significant correlation with particle composition, but a weak dependence on relative humidity. The uptake coefficients obtained are compared to existing parameterizations based on laboratory datasets and with other values obtained by analysis of field data.

Aerosol hygroscopic properties were linked to its chemical composition by using complementary online mass spectrometric techniques in a comprehensive chemical characterization study at a rural mountaintop station in central Germany in August 2012. In particular, atmospheric pressure chemical ionization mass spectrometry ((-)APCI-MS) provided measurements of organic acids, organosulfates, and nitrooxy-organosulfates in the particle phase at 1 min time resolution. Offline analysis of filter samples enabled us to determine the molecular composition of signals appearing in the online (-)APCI-MS spectra. Aerosol mass spectrometry (AMS) provided quantitative measurements of total submicrometer organics, nitrate, sulfate, and ammonium. Inorganic sulfate measurements were achieved by semionline ion chromatography and were compared to the AMS total sulfate mass. We found that up to 40% of the total sulfate mass fraction can be covalently bonded to organic molecules. This finding is supported by both on- and offline soft ionization techniques, which confirmed the presence of several organosulfates and nitrooxy-organosulfates in the particle phase. The chemical composition analysis was compared to hygroscopicity measurements derived from a cloud condensation nuclei counter. We observed that the hygroscopicity parameter (κ) that is derived from organic mass fractions determined by AMS measurements may overestimate the observed κ up to 0.2 if a high fraction of sulfate is bonded to organic molecules and little photochemical aging is exhibited.

We describe a thermal dissociation cavity ring-down spectrometer (TD-CRDS) for measurement of ambient NO2, total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs). The spectrometer has two separate cavities operating at ∼ 405.2 and 408.5 nm. One cavity (reference) samples NO2 continuously from an inlet at ambient temperature, the other samples sequentially from an inlet at 473 K in which PNs are converted to NO2 or from an inlet at 723 K in which both PNs and ANs are converted to NO2, difference signals being used to derive mixing ratios of ΣPNs and ΣANs. We describe an extensive set of laboratory experiments and numerical simulations to characterise the fate of organic radicals in the hot inlets and cavity and derive correction factors to account for the bias resulting from the interaction of peroxy radicals with ambient NO and NO2. Finally, we present the first measurements and comparison with other instruments during a field campaign, outline the limitations of the present instrument and provide an outlook for future improvements.

Abstract. We analysed the extensive dataset from the HUMPPA-COPEC 2010 and the HOPE 2012 field campaigns in the boreal forest and rural environments of Finland and Germany, respectively, and estimated the abundance of stabilised Criegee intermediates (SCI) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the afore-mentioned campaigns is caused at least partially by SCI. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. The background OH concentration also complements the previously underestimated production rate of sulfuric acid and is consistent with its scavenging through the addition of sulphur dioxide. A central estimate of the SCI concentration of ~ 5 × 104 molecules cm−3 (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCI, though, over the boreal forest, significant for the conversion of SO2 into H2SO4. The large uncertainties in these calculations, owing to the many unknowns in the chemistry of Criegee intermediates, emphasise the need to better understand these processes and their potential effect on the self-cleaning capacity of the atmosphere.

Meeting abstract fro AOGS 2016 Beijing for an oral presentation of results from the CYPHEX 2014 measurement campaign.