Search

We present an aerosol cloud condensation nuclei (CCN) closure study over the north-east Atlantic Ocean using six approximating methods. The CCN number concentrations (NCCN) were measured at four discrete supersaturations (SSs; 0.25 %, 0.5 %, 0.75 % and 1.0 %). Concurrently, aerosol number size distribution, sub-saturation hygroscopic growth factor and bulk PM1 chemical composition were obtained at matching time resolution and after a careful data validation exercise. Method A used a constant bulk hygroscopicity parameter κ of 0.3; method B used bulk PM1 chemical composition measured by an aerosol mass spectrometer (AMS); method C utilised a single growth factor (GF) size (165 nm) measured by a humidified tandem differential mobility analyser (HTDMA); method D utilised size-dependent GFs measured at 35, 50, 75, 110 and 165 nm; method E divided the aerosol population into three hygroscopicity modes (near-hydrophobic, more-hygroscopic and sea-salt modes), and the total CCN number in each mode was cumulatively added up; method F used the full-size-scale GF probability density function (GF–PDF) in the most complex approach. The studied periods included high-biological-activity and low-biological-activity seasons in clean marine and polluted continental air masses to represent and discuss the most contrasting aerosol populations. Overall, a good agreement was found between estimated and measured NCCN with linear regression slopes ranging from 0.64 to 1.6. The temporal variability was captured very well, with Pearson's R value ranging from 0.76 to 0.98 depending on the method and air mass type. We further compared the results of using different methods to quantify the impact of size-dependent hygroscopicity and mixing state and found that ignoring size-dependent hygroscopicity induced overestimation of NCCN by up to 12 %, and ignoring a mixing state induced overestimation of NCCN by up to 15 %. The error induced by assuming an internal mixing in highly polluted cases was largely eliminated by dividing the full GF–PDF into three conventional hygroscopic modes, while assuming an internal mixing in clean marine aerosol did not induce significant error.

Nitrated aromatic compounds (NACs) are a group of key chromophores for brown carbon (light-absorbing organic carbon, i.e., BrC) aerosol, which affects radiative forcing. The chemical composition and sources of NACs and their contributions to BrC absorption, however, are still not well understood. In this study, PM 2.5 -bound NACs in Xi'an, Northwest China, were investigated for 112 daily PM 2.5 filter samples from 2015 to 2016. Both the total concentrations and contributions from individual species of NACs show distinct seasonal variations. The seasonally averaged concentrations of NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56 ng m −3 (winter). Thereinto, 4-nitrophenol is the major NAC component in spring (58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol dominate in summer (70 %), and the concentrations of 4-nitrocatechol and 4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species show different seasonal patterns in concentrations, indicating differences in emissions and formation pathways. Source apportionment results using positive matrix factorization (PMF) further show large seasonal differences in the sources of NACs. Specifically, in summer, NACs were highly influenced by secondary formation and vehicle emissions ( ∼ 80 %), while in winter, biomass burning and coal combustion contributed the most ( ∼ 75 %). Furthermore, the light absorption contributions of NACs to BrC are wavelength-dependent and vary greatly by season, with maximum contributions at ∼ 330 nm in winter and fall and ∼ 320 nm in summer and spring. The differences in the contribution to light absorption are associated with the higher mass fractions of 4-nitrocatechol ( λ max⁡ = 345 nm) and 4-nitrophenol ( λ max⁡ = 310 nm) in fall and winter, 4-nitrophenol in spring, and 5-nitrosalicylic acid ( λ max⁡ = 315 nm) and 4-nitrophenol in summer. The mean contributions of NACs to BrC light absorption at a wavelength of 365 nm in different seasons are 0.14 % (spring), 0.09 % (summer), 0.36 % (fall), and 0.91 % (winter), which are about 6–9 times higher than their mass fractional contributions of carbon in total organic carbon. Our results indicate that the composition and sources of NACs have profound impacts on the BrC light absorption.

11 pages, 3 figures, supporting information https://doi.org/10.1021/acs.est.0c00695, We present shipborne measurements of size-resolved concentrations of aerosol components across ocean waters next to the Antarctic Peninsula, South Orkney Islands, and South Georgia Island, evidencing aerosol features associated with distinct eco-regions. Nonmethanesulfonic acid Water-Soluble Organic Matter (WSOM) represented 6–8% and 11–22% of the aerosol PM1 mass originated in open ocean (OO) and sea ice (SI) regions, respectively. Other major components included sea salt (86–88% OO, 24–27% SI), non sea salt sulfate (3–4% OO, 35–40% SI), and MSA (1–2% OO, 11–12% SI). The chemical composition of WSOM encompasses secondary organic components with diverse behaviors: while alkylamine concentrations were higher in SI air masses, oxalic acid showed higher concentrations in the open ocean air. Our online single-particle mass spectrometry data exclude a widespread source from sea bird colonies, while the secondary production of oxalic acid and sulfur-containing organic species via cloud processing is suggested. We claim that the potential impact of the sympagic planktonic ecosystem on aerosol composition has been overlooked in past studies, and multiple eco-regions act as distinct aerosol sources around Antarctica, The study was supported by the Spanish Ministry of Economy through project BIO-NUC (CGL2013-49020-R), PI-ICE (CTM2017–89117-R) and the Ramon y Cajal fellowship (RYC-2012-11922), and by the EU though the FP7-PEOPLE-2013-IOF programme (Project number 624680, MANU – Marine Aerosol NUcleations), all to M.D., and PEGASO (CTM2012-37615) to R.S., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Organosulfur compounds are important components of secondary organic aerosols (SOA). While the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS) has been extensively used in aerosol studies, the response of the AMS to organosulfur compounds is not well-understood. Here, we investigated the fragmentation patterns of organosulfurs and inorganic sulfates in the AMS, developed a method to deconvolve total sulfate into components of inorganic and organic origins, and applied this method in both laboratory and field measurements. Apportionment results from laboratory isoprene photooxidation experiment showed that with inorganic sulfate seed, sulfate functionality of organic origins can contribute ∼7% of SOA mass at peak growth. Results from measurements in the Southeastern U.S. showed that 4% of measured sulfate is from organosulfur compounds. Methanesulfonic acid was estimated for measurements in the coastal and remote marine boundary layer. We explored the application of this method to unit mass-resolution data, where it performed less well due to interferences. Our apportionment results demonstrate that organosulfur compounds could be a non-negligible source of sulfate fragments in AMS laboratory and field data sets. A reevaluation of previous AMS measurements over the full range of atmospheric conditions using this method could provide a global estimate/constraint on the contribution of organosulfur compounds.

The atmosphere over the Atlantic Ocean is highly impacted by human activities on the surrounding four major continents. Globally, human activity creates significant burdens for the sustainability of key Earth systems, pressuring the planetary boundaries of environmental sustainability. Here, we propose a science-based integrated approach addressing linked science and policy challenges in the North Atlantic. There is a unique combination of ongoing anthropogenic changes occurring in the coupled atmosphere–ocean environment of the region related to climate, air and water quality, the biosphere and cryosphere. This is matched by a unique potential for the societies that surround the North Atlantic to systematically address these challenges in a dynamic and responsive manner. Three key linked science-policy challenges to be addressed as part of this proposed integrated regional approach are: (1) understanding physical and dynamic changes, (2) sustaining human and ecosystem health and (3) reducing existing knowledge gaps on the carbon budget and the Earth’s energy balance. We propose a North Atlantic multidisciplinary scientific assessment system and observation network to address these thematic challenges. We propose to build on and link with the existing research activities and observational networks and infrastructures to specifically address the key North Atlantic challenges that encompass a range of policy areas. This will strengthen the institutional response to weather, climate, environmental and ecological threats and reduce societal risk.

Significance Recycling of reactive iodine from heterogeneous processes on sea-salt aerosol was hypothesized over two decades ago to play an important role in the atmospheric cleansing capacity. However, the understanding of this mechanism has been limited to laboratory studies and has not been confirmed in the atmosphere until now. We present atmospheric measurement of gas-phase iodine interhalogen species and show that their production via heterogeneous processing on marine aerosols is remarkably fast. These observations reveal that the atmospheric recycling of atomic iodine through photolysis of iodine interhalogen species is more efficient than previously thought, which is ultimately expected to lead to higher ozone loss and faster new particle formation in the marine environment., Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride [ICl] and iodine monobromide [IBr]) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought. These results indicate that the fast formation of iodine interhalogens, together with their rapid photolysis, results in more efficient recycling of atomic iodine than currently considered in models. Photolysis of the observed ICl and IBr leads to a 32% increase in the daytime average of atomic iodine production rate, thereby enhancing the average daytime iodine-catalyzed ozone loss rate by 10 to 20%. Our findings provide direct field evidence that the autocatalytic mechanism of iodine release from marine aerosol is important in the atmosphere and can have significant impacts on atmospheric oxidation capacity.

The ways in which marine biological activity affects climate, by modifying aerosol properties, are not completely understood, causing high uncertainties in climate predictions. In this work, in situ measurements of aerosol chemical composition, particle number size distribution, cloud condensation nuclei (CCN), and ice-nucleating particle (INP) number concentrations are combined with high-resolution sea surface chlorophyll-a concentration (CHL) and back-trajectory data to elucidate the relationship between oceanic biological activity and marine aerosol. The measurements were performed during an intensive field campaign conducted in late summer (August–September) 2015 at the Mace Head Research Station (MHD). At the short time scale (1–2months) of the experiment, we observed a clear dependency of the main aerosol physicochemical and cloud-relevant properties on the patterns of biological activity, in specific oceanic regions with a delayed response of about 1–3weeks. The oceanic region comprised between 47°–57°N and 14°–30°W was identified as the main source of biogenic aerosols during the campaign, with hints of some minor influence of waters up to the Greenland coast. These spatial and temporal relationships demonstrate that the marine biota influences aerosol properties under a variety of features up to the most cloud-relevant properties. Such dependency of aerosol properties with oceanic biological activity was previously reported over the North Atlantic Ocean only for multiyear data sets, where the correlation may be enhanced by coincident seasonalities. A better knowledge of these short time scale interactions may lead to a significant improvement in understanding the ocean-atmosphere-cloud system, with important impacts on climate science.

The chromophores responsible for light absorption in atmospheric brown carbon (BrC) are not well characterized, which hinders our understanding of BrC chemistry, the links with optical properties, and accurate model representations of BrC to global climate and atmospheric oxidative capacity. In this study, the light absorption properties and chromophore composition of three BrC fractions of different polarities were characterized for urban aerosol collected in Xi'an and Beijing in winter 2013-2014. These three BrC fractions show large differences in light absorption and chromophore composition, but the chromophores responsible for light absorption are similar in Xi'an and Beijing. Water-insoluble BrC (WI-BrC) fraction dominates the total BrC absorption at 365 nm in both Xi'an (51 ± 5%) and Beijing (62 ± 13%), followed by a humic-like fraction (HULIS-BrC) and high-polarity water-soluble BrC. The major chromophores identified in HULIS-BrC are nitrophenols and carbonyl oxygenated polycyclic aromatic hydrocarbons (OPAHs) with 2-3 aromatic rings (in total 18 species), accounting for 10% and 14% of the light absorption of HULIS-BrC at 365 nm in Xi'an and Beijing, respectively. In comparison, the major chromophores identified in WI-BrC are PAHs and OPAHs with 4-6 aromatic rings (in total 16 species), contributing 6% and 8% of the light absorption of WI-BrC at 365 nm in Xi'an and Beijing, respectively.

Sulfate and nitrate from secondary reactions remain as the most abundant inorganic species in atmospheric particle matter (PM). Their formation is initiated by oxidation (either in gas phase or particle phase), followed by neutralization reaction primarily by NH3, or by other alkaline species such as alkaline metal ions if available. The different roles of NH3 and metal ions in neutralizing H2SO4 or HNO3, however, are seldom investigated. Here we conducted semi-continuous measurements of SO4 2−, NO3 −, NH4 +, and their gaseous precursors, as well as alkaline metal ions (Na+, K+, Ca2+, and Mg2+) in wintertime Beijing. Analysis of aerosol acidity (estimated from a thermodynamic model) indicated that preferable sulfate formation was related to low pH conditions, while high pH conditions promote nitrate formation. Data in different mass fraction ranges of alkaline metal ions showed that in some ranges the role of NH3 was replaced by alkaline metal ions in the neutralization reaction of H2SO4 and HNO3 to form particulate SO4 2− and NO3 −. The relationships between mass fractions of SO4 2− and NO3 − in those ranges of different alkaline metal ion content also suggested that alkaline metal ions participate in the competing neutralization reaction of sulfate and nitrate. The implication of the current study is that in some regions the chemistry to incorporate sulfur and nitrogen into particle phase might be largely affected by desert/fugitive dust and sea salt, besides NH3. This implication is particularly relevant in coastal China and those areas with strong influence of dust storm in the North China Plain (NCP), both of which host a number of megacities with deteriorating air quality.

Sulfate aerosols are typically the dominant source of cloud condensation nuclei (CCN) over remote oceans and their abundance is thought to be the dominating factor in determining oceanic cloud brightness. Their activation into cloud droplets depends on dynamics (i.e. vertical updrafts) and competition with other potential CCN sources for the condensing water. We present new experimental results from the remote Southern Ocean illustrating that, for a given updraft, the peak supersaturation reached in cloud, and consequently the number of droplets activated on sulfate nuclei, is strongly but inversely proportional to the concentration of sea-salt activated despite a 10-fold lower abundance. Greater sea-spray nuclei availability mostly suppresses sulfate aerosol activation leading to an overall decrease in cloud droplet concentrations; however, for high vertical updrafts and low sulfate aerosol availability, increased sea-spray can augment cloud droplet concentrations. This newly identified effect where sea-salt nuclei indirectly controls sulfate nuclei activation into cloud droplets could potentially lead to changes in the albedo of marine boundary layer clouds by as much as 30%. The research leading to these results has received funding from SFI under MaREI; the European Union’s Seventh Framework Programme (FP7/2007–2013) project BACCHUS under grant agreement n_603445; Spanish Ministry of Economy and Competitiveness (MINECO) as part of the PEGASO (Ref.: CTM2012-37615) and BIONUC (Ref: CGL2013-49020-R) projects. The Antarctic cruise that led to this study was organised by R. Simo and M. Dall’Osto from the Institut de Ciéncies del Mar (CSIC), Barcelona, Catalonia, Spain. peer-reviewed

The Guanzhong basin is a part of the three top priority regions in China's blue sky action as of 2019. Understanding the chemical composition, sources, and atmospheric process of aerosol in this region is therefore imperative for improving air quality. In this study, we present, for the first time, the seasonal variations of organic aerosol (OA) in Xi'an, the largest city in the Guanzhong basin. Biomass burning OA (BBOA) and oxidized OA (OOA) contributed >50% of OA in both autumn and winter. The average concentrations of BBOA in autumn (14.8 ± 5.1 μg m-3) and winter (11.6 ± 6.8 μg m-3) were similar. The fractional contribution of BBOA to total OA, however, decreased from 31.9% in autumn to 15.3% in winter, because of enhanced contributions from other sources in winter. The OOA fraction in OA increased largely from 20.9% in autumn to 34.9% in winter, likely due to enhanced emissions of precursors and stagnant meteorological conditions which facilitate the accumulation and secondary formation. A large increase in OOA concentration was observed during polluted days, by a factor of ~4 in autumn and ~6 in winter compared to clean days. In both seasons, OOA formation was most likely dominated by photochemical oxidation when aerosol liquid water content was

The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts) in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA). In atmospheric research, lightweight RPAs (

Enhanced secondary aerosol formation was observed during the COVID-19 lockdown in Xi'an, especially for polluted episodes. More oxidized‑oxygenated organic aerosol (MO-OOA) and sulfate showed the dominant enhancements, especially in large particle-mode. Meanwhile, relative humidity (RH) showed a positive promotion on the formation of sulfate and MO-OOA during the lockdown, but had no obvious correlation with less oxidized‑oxygenated organic aerosol (LO-OOA) or nitrate. Organosulfurs (OS) displayed a higher contribution (~58%) than inorganic sulfate to total sulfate enhancement in the polluted episode during the lockdown. Although the total nitrate (TN) decreased during the lockdown ascribing to a larger reduction of inorganic nitrate, organic nitrate (ON) showed an obvious increase from pre-lockdown (0.5 ± 0.6 μg m-3 and 1 ± 2% of TN) to lockdown (5.3 ± 3.1 μg m-3 and 17 ± 9% of TN) in the polluted case (P < 0.05). In addition, RH also displayed a positive promotion on the formation of ON and OS, and the increases of both OS and ON were much efficient in the nighttime than in the daytime. These results suggest that higher RH and stagnant meteorology might facilitate the sulfate and MO-OOA enhancement, especially in the nighttime, which dominated the secondary aerosol enhancement in haze pollution during the lockdown.

9 pages, 5 figures, 1 table, supplementary data https://doi.org/10.1016/j.atmosenv.2019.117160, Using a number of datasets from single particle Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS) measurements, we show only a minor presence of Organic Nitrogen (ON) species in Saharan dust particles (aerosol size range 0.2–3 μm) collected at their origin. ON enhancement is not observed on Saharan dust particles after atmospheric transport (48–96 h) either over the Tropical Ocean in the vicinity of Cape Verde, over the North Atlantic Ocean. In the negative ATOFMS mass spectra, signals due to ON species were found weaks in biological particles (rich in potassium and phosphate) in their source area, and signals due to alkylamines in the positive ATOFMS mass spectra were not found. In striking contrast, biological particles travelling within aerosol dust plumes are found to be enriched in ON species - including alkylamines - in North Atlantic Ocean air (Mace Head, Ireland), as seen in both positive and negative ATOFMS mass spectra. Contrary to filter based aerosol techniques which report ON enrichment within Saharan dust, our single particle mass spectrometry data - allowing study of the aerosol mixing state - suggests that the aging biological particles and not the associated transported aging Saharan dust may be a source of ON species. We suggest biogeochemical processes occurring in the atmosphere in which biological particles are responsible for ON production. This may be an important source of nutrients to the ocean via atmospheric deposition, The study was also supported by the Spanish Ministry of Economy through project PI-ICE (CTM2017-89117-R) and the Ramon y Cajal fellowship (RYC-2012-11922), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Many efforts have been dedicated toward understanding the role of biogenic sulfur particles as a climate regulator. Herein, we investigate the relationship between the atmospheric concentration of methanesulfonic acid (MSA) and phytoplankton biomass in the Mediterranean Sea by identifying the main MSA source regions during a springtime intensive observation period. The study approach combines i) spatio-temporal correlation analysis between in situ aerosol data measured in April 2016 at Capo Granitola (southern Sicily), and high-resolution ocean color composites, ii) back-trajectory analysis, and iii) potential source contribution function (PSCF) algorithm. The southwestern Mediterranean region (between Sardinia and the Algerian coast) was identified as the most probable dimethylsulfide (DMS) source region contributing to the observed MSA concentrations. Conversely, the blooming northwestern Mediterranean Sea region did not appear to contribute significantly. The present analysis shows that the reasons may be biotic (phytoplankton type, stress level) or abiotic (sea surface temperature), or a combination of both. We also postulate that the identified source region is associated with the production of non-sea-salt-sulfate and secondary organic aerosols from the processing of sea-released volatile organic compounds.

Special issue Marine organic matter: from biological production in the ocean toorganic aerosol particles and marine clouds (ACP/OS inter-journalSI).-- 15 pages, 8 figures, 1 table, supplement https://doi.org/10.5194/acp-20-4193-2020, The concentrations of submicron aerosol particles in maritime regions around Antarctica are influenced by the extent of sea ice. This effect is two ways: on one side, sea ice regulates the production of particles by sea spray (primary aerosols); on the other side, it hosts complex communities of organisms emitting precursors for secondary particles. Past studies documenting the chemical composition of fine aerosols in Antarctica indicate various potential primary and secondary sources active in coastal areas, in offshore marine regions, and in the sea ice itself. In particular, beside the well-known sources of organic and sulfur material originating from the oxidation of dimethylsulfide (DMS) produced by microalgae, recent findings obtained during the 2015 PEGASO cruise suggest that nitrogen-containing organic compounds are also produced by the microbiota colonizing the marginal ice zone. To complement the aerosol source apportionment performed using online mass spectrometric techniques, here we discuss the outcomes of offline spectroscopic analysis performed by nuclear magnetic resonance (NMR) spectroscopy. In this study we (i) present the composition of ambient aerosols over open-ocean waters across bioregions, and compare it to the composition of (ii) seawater samples and (iii) bubble-bursting aerosols produced in a sea-spray chamber onboard the ship. Our results show that the process of aerosolization in the tank enriches primary marine particles with lipids and sugars while depleting them of free amino acids, providing an explanation for why amino acids occurred only at trace concentrations in the marine aerosol samples analyzed. The analysis of water-soluble organic carbon (WSOC) in ambient submicron aerosol samples shows distinct NMR fingerprints for three bioregions: (1) the open Southern Ocean pelagic environments, in which aerosols are enriched with primary marine particles containing lipids and sugars; (2) sympagic areas in the Weddell Sea, where secondary organic compounds, including methanesulfonic acid and semivolatile amines abound in the aerosol composition; and (3) terrestrial coastal areas, traced by sugars such as sucrose, emitted by land vegetation. Finally, a new biogenic chemical marker, creatinine, was identified in the samples from the Weddell Sea, providing another confirmation of the importance of nitrogen-containing metabolites in Antarctic polar aerosols, The cruise was funded by the Spanish Ministry of Economy through projects PEGASO (CTM2012-37615) and Bio-Nuc (CGL2013-49020-R). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007–2013) Project BACCHUS under grant agreement no. 603445. The research activities of CNR were also supported by the project AirSEaLab: Progetto Laboratori Congiunti, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

One hydrochlorofluorocarbon and two hydrofluorocarbons (HCFC-22, HFC-125, and HFC-152a) were measured in air samples at the Cape Point observatory (CPT), South Africa, during 2017. These data represent the first such atmospheric measurements of these compounds from southwestern South Africa (SWSA). Baseline atmospheric growth rates were estimated to be 8.36, 4.10, and 0.71 ppt year-1 for HCFC-22, HFC-125, and HFC-152a, respectively. The CPT measurements were combined with an inverse model to investigate emissions from SWSA. For all three halocarbons, Cape Town was found to be the dominant source within SWSA. These estimates were extrapolated, based on population statistics, to estimate emissions for the whole of South Africa. We estimate South Africa's 2017 emissions to be 3.0 (1.6-4.4), 0.8 (0.5-1.2), and 1.1 (0.6-1.6) Gg year-1 for HCFC-22, HFC-125, and HFC-152a, respectively. For all three halocarbons, South Africa's contribution to global emissions is small (

Biogenic volatile organic compound (BVOC) emissions are one of the essential inputs for chemical transport models (CTMs), but their estimates are associated with large uncertainties, leading to significant influence on air quality modelling. This study aims to investigate the effects of using different BVOC emission models on the performance of a CTM in simulating secondary pollutants, i.e. ozone, organic, and inorganic aerosols. European air quality was simulated for the year 2011 by the regional air quality model Comprehensive Air Quality Model with Extensions (CAMx) version 6.3, using BVOC emissions calculated by two emission models: the Paul Scherrer Institute (PSI) model and the Model of Emissions of Gases and Aerosol from Nature (MEGAN) version 2.1. Comparison of isoprene and monoterpene emissions from both models showed large differences in their general amounts, as well as their spatial distribution in both summer and winter. MEGAN produced more isoprene emissions by a factor of 3 while the PSI model generated 3 times the monoterpene emissions in summer, while there was negligible difference (∼4 %) in sesquiterpene emissions associated with the two models. Despite the large differences in isoprene emissions (i.e. 3-fold), the resulting impact in predicted summertime ozone proved to be minor (60 ppb). A much larger effect of the different BVOC emissions was found for the secondary organic aerosol (SOA) concentrations. The higher monoterpene emissions (a factor of ∼3) by the PSI model led to higher SOA by ∼110 % on average in summer, compared to MEGAN, and lead to better agreement between modelled and measured organic aerosol (OA): the mean bias between modelled and measured OA at nine measurement stations using Aerodyne aerosol chemical speciation monitors (ACSMs) or Aerodyne aerosol mass spectrometers (AMSs) was reduced by 21 %–83 % at rural or remote stations. Effects on inorganic aerosols (particulate nitrate, sulfate, and ammonia) were relatively small (, Acknowledgements. We would like to thank the TNO for providing anthropogenic emissions, the European Centre for Medium-Range Weather Forecasts (ECMWF) for the access to the meteorological data, the European Environmental Agency (EEA) for the air quality data, and the National Aeronautics and Space Administration (NASA) and its data-contributing agencies (NCAR, UCAR) for the TOMS and MODIS data, the global air quality model data, and the TUV model. Simulations of WRF and CAMx models were performed at the Swiss National Supercomputing Centre (CSCS). We thank the EBAS database of the Norwegian Institute for Air Research (NILU) for the measurement data of isoprene concentration. We are grateful to RAMBOLL for the valuable support for CAMx. We thank the ACSM/AMS data providers, namely Stefania Gilardoni for the Bologna and San Pietro Capofiume stations, Nicolas Marchand and the MASSALYA instrumental platform (https://lce.univ-amu.fr/en/massalya, last access: 12 March 2019 for Marseille, Olivier Favez (INERIS) and the whole SIRTA team for measurements conducted in the Paris area in the frame of the EU FP7 ACTRIS programme under the grant agreement no. 262254, Kalliopi Florou for Finokalia, and Liqing Hao and Annele Virtanen for SMEAR II Hyytiälä. EPA-Ireland (AEROSOURCE, 2016-CCRP-MS-31) is acknowledged, as well as EGAR group from IDAEA-CSIC (special mention to Anna Ripoll and An-drés Alastuey) and Generalitat de Catalunya (AGAUR 2017 SGR41). María Cruz Minguillón acknowledges the Ramón y Cajal fellowship awarded by the Spanish Ministry of Economy, Industry and Competitiveness.

Aerosol principal sources and sinks over eastern North Atlantic waters were studied through the deployment of an aerosol chemistry gradient sampling system. The chemical gradients of primary and secondary aerosol components – specifically, sea salt (SS), water-insoluble organic matter (WIOM), water-soluble organic matter (WSOM), nitrate, ammonium, oxalate, amines, methanesulfonic acid (MSA) and water-soluble organic nitrogen (WSON) – were examined in great detail. Sea salt fluxes were estimated by the boundary layer box model and ranged from 0.3 to 3.5 ng m−2 s−1 over the wind speed range of 5–12 m s−1 and compared well with the derived fluxes from existing sea salt source parameterisations. The observed seasonal pattern of sea salt gradients was mainly driven by wind stress in addition to the yet unquantified effect of marine OM modifying fractional contributions of SS and OM in sea spray. WIOM gradients were a complex combination of rising and waning biological activity, especially in the flux footprint area, and wind-driven primary sea spray production supporting the coupling of recently developed sea spray and marine OM parameterisations.

To mitigate air pollution in China, a legislative ‘Air Pollution Prevention and Control Action Plan’ has been implemented by the Chinese government since 2013. There is, however, a lack of investigations for long-term trends in the composition, sources and evolution processes of PM1 (particulate matter with diameter less than 1 μm) after the implementation. To evaluate the effectiveness of these control measures, we present a year-long real-time measurement of the chemical composition of PM1 at an urban site in Beijing from November 2014 to November 2015, and the results are compared with previous studies from 2008 to 2013 to gain insights into the variations of the chemical composition and sources of PM1 in Beijing. Large seasonal differences were observed in the mass concentrations of PM1 species and general declining trend was observed in the last seven years. Specifically, the annual averages of mass concentrations in 2014–2015 decrease by 16–43% (PM1), 23–43% (organic aerosol, OA), 38–68% (sulfate), 26–51% (nitrate), 18–33% (ammonium) and 27–38% (chloride) compared to those from 2008 to 2013. During winter and summer, the seasonal mass concentrations of sulfate and nitrate show more significant declines especially in summer 2008 (79% and 81%) and summer 2011 (76% and 77%). The nitrate-to-sulfate ratio is higher in 2014–2015 (1.5 ± 0.6) than that in 2013 (1.0 ± 0.3), largely due to significant reduction in SO2 emissions, suggesting that nitrate is becoming more important than sulfate in particulate pollution in Beijing. OA is the dominant PM1 fraction (>45%) in all seasons and the mass concentrations/contributions of both primary and secondary OA show different seasonality. As for the more oxidized oxygenated OA (MO-OOA) and less oxidized oxygenated OA (LO-OOA), the contributions of MO-OOA are much higher than those of LO-OOA (27–62% vs. 6–26%) in both high-pollution and low-pollution days. Aqueous-phase processes are found to facilitate the formation of MO-OOA while photochemical oxidation formation is a major contributor of LO-OOA in winter, and photochemical oxidation plays a major role in the formation of MO-OOA in summer and fall. The current study provides a comprehensive seasonal comparison of chemical composition and formation of PM1 in Beijing and a pacesetter in tackling PM pollution for other equally polluted megacities, after implementation of more stringent control measures after 2013.

Dall'Osto, Manuel ... et al.-- 11 pages, 4 figures, supplementary material https://dx.doi.org/10.1038/s41598-017-17343-9, The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future, We gratefully acknowledge support by the German Federal Environment Agency (Umweltbundesamt), grants no. 351 03 031 and 351 01 038, and UFOPLAN grant 3703 43 200 (title “Erfassung der Zahl feiner und ultrafeiner Partikel in der Außenluft”). [...] The study was funded by the Spanish Ministry of Economy through projects BIO-NUC (CGL2013-49020-R), and by the EU though the FP7-PEOPLE-2013-IOF programme (Project number 624680, MANU – Marine Aerosol NUcleations) and the Ramon y Cajal fellowship (RYC-2012-11922).The National Centre for Atmospheric Science NCAS Birmingham group is funded by the UK Natural Environment Research Council

Source apportionment studies of particulate matter (PM) link chemical composition to emission sources, while health risk analyses link health outcomes and chemical composition. There are limited studies to link emission sources and health risks from ambient measurements. We show such an attempt for particulate trace elements. Elements in PM2.5 were measured in wintertime Beijing, and the total concentrations of 14 trace elements were 1.3-7.3 times higher during severe pollution days than during low pollution days. Fe, Zn, and Pb were the most abundant elements independent of the PM pollution levels. Chemical fractionation shows that Pb, Mn, Cd, As, Sr, Co, V, Cu, and Ni were present mainly in the bioavailable fraction. Positive matrix factorization was used to resolve the sources of particulate trace elements into dust, oil combustion, coal combustion, and traffic-related emissions. Traffic-related emission contributed 65% of total mass of the measured elements during low pollution days. However, coal combustion dominated (58%) during severe pollution days. By combining element-specific health risk analyses and source apportionment results, we conclude that traffic-related emission dominates the health risks by particulate trace elements during low pollution days, while coal combustion becomes equally or even more important during moderate and severe pollution days.

The sources, formation mechanism and amount of organosulfates (OS) in atmospheric aerosol are not yet well understood, partly due to the lack of authentic standards for quantification. In this study, we report an improved robust procedure for the synthesis of organosulfates with different functional groups. Nine authentic organosulfate standards were synthesized and four standards (benzyl sulfate, phenyl sulfate, glycolic acid sulfate, and hydroxyacetone sulfate) were used to quantify their ambient concentrations. The authentic standards and ambient aerosol samples were analyzed using an optimized ultra performance liquid chromatography–electrospray ionization-tandem mass spectrometric method (UPLC–ESI–MS/MS). The recovery ranged from 80.4 to 93.2 %, the limits of detection and limits of quantification obtained were 1.1–16.7 and 3.4–55.6 pg m−3, respectively. Measurements of ambient aerosol particle samples collected in winter 2013/2014 in urban Xi'an, northwestern China, show that glycolic acid sulfate (77.3 ± 49.2 ng m−3) is the most abundant species of the identified organosulfates followed by hydroxyacetone sulfate (1.3 ± 0.5 ng m−3), phenyl sulfate (0.14 ± 0.09 ng m−3), and benzyl sulfate (0.04 ± 0.01 ng m−3). Except for hydroxyacetone sulfate, which seems to form mainly from biogenic emissions in this region, the organosulfates quantified during winter in Xi'an show an increasing trend with an increase in the mass concentrations of organic carbon indicating their anthropogenic origin.

Light-absorbing organic carbon (i.e., brown carbon or BrC) in the atmospheric aerosol has significant contribution to light absorption and radiative forcing. However, the link between BrC optical properties and chemical composition remains poorly constrained. In this study, we combine spectrophotometric measurements and chemical analyses of BrC samples collected from July 2008 to June 2009 in urban Xi'an, Northwest China. Elevated BrC was observed in winter (5 times higher than in summer), largely due to increased emissions from wintertime domestic biomass burning. The light absorption coefficient of methanol-soluble BrC at 365 nm (on average approximately twice that of water-soluble BrC) was found to correlate strongly with both parent polycyclic aromatic hydrocarbons (parent-PAHs, 27 species) and their carbonyl oxygenated derivatives (carbonyl-OPAHs, 15 species) in all seasons (r(2) > 0.61). These measured parent-PAHs and carbonyl-OPAHs account for on average similar to 1.7% of the overall absorption of methanol-soluble BrC, about 5 times higher than their mass fraction in total organic carbon (OC, similar to 0.35%). The fractional solar absorption by BrC relative to element carbon (EC) in the ultraviolet range (300-400 nm) is significant during winter (42 +/- 18% for water-soluble BrC and 76 +/- 29% for methanol-soluble BrC), which may greatly affect the radiative balance and tropospheric photochemistry and therefore the climate and air quality.

Article, Cloud condensation nuclei counter (CCNC) measurements performed at 14 locations around the world within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations – exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5 % significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6 %. The same is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol–cloud interactions in various environments., published version, http://purl.org/eprint/status/PeerReviewed

Sea spray aerosol (SSA) generated by bubble bursting at the ocean surface is an important component of aerosol-cloud interactions over remote oceans, providing the atmosphere with ice-nucleating particles (INPs) or particles required for heterogeneous ice nucleation. Studies have shown that organic INPs are emitted during phytoplankton blooms, but changes in INP number concentrations (nINPs) due to ocean biological activity have not been directly demonstrated in natural SSA. In this study, a clean sector sampler was used to differentiate ice nucleation and composition of pristine SSA from terrestrial aerosol at the Mace Head Research Station in August 2015. Average nINPs active at −15 °C (nINPs,−15 °C) were 0.0011 L−1, and large variability (up to a factor of 200) was observed for INPs active warmer than −22 °C. Highest nINPs in the clean sector occurred during a period of elevated marine organic aerosol from offshore biological activity (M1, nINPs,−15 °C = 0.0077 L−1). A peak in nINPs was also observed in terrestrial organic aerosol (T1, nINPs,−15 °C = 0.0076 L−1). The impacts of heating and hydrogen peroxide digestion on nINPs indicate that INPs at Mace Head Research Station were largely organic and that INPs observed during M1 and T1 were biological (i.e., protein containing). Complexities of predicting increases in nINPs due to offshore biological activity are explored. A parameterization for pristine SSA INPs over the North Atlantic Ocean was developed, illustrating that SSA is associated with a factor of 1,000 fewer ice-nucleating sites per surface area of aerosol compared to mineral dust. ©2018. American Geophysical Union. All Rights Reserved.

Atmospheric aerosol particles (also known as particulate matter) are central to the cause of the two greatest threats to human security: air pollution (~5 million premature deaths per year) and climate change (~0.5 million per year). Addressing these threats requires an understanding of particulate matter sources responsible for both extreme air pollution immediately affecting human health and less extreme levels affecting climate over longer timescales. Here, extraordinary levels of air pollution, with submicrometre aerosol (PM1) mass concentration surpassing 300 µg m−3, were observed in a moderately sized European city and are attributed to emissions from residential solid fuel—specifically peat and wood, often promoted as ‘slow-renewable’, ‘low-carbon’ or ‘carbon-neutral’ biomass. Using sophisticated fingerprinting techniques, we find that consumption of peat and wood in up to 12% and 1% of households, respectively, contributed up to 70% of PM1. The results from this approach can better inform emissions reduction policies and help to ensure the most appropriate air pollution sources are targeted. Given the far greater abundance of solid fuels and concomitant emissions required to match the calorific benefit of liquid fuels, even modest increases in the consumption of ‘green’-marketed solid fuels will disproportionally increase the frequency of extreme pollution events. Understanding the sources of particulate matter responsible for extreme air pollution and climate change is critical for designing adequate policies to protect the wellbeing of citizens. This study shows that extraordinary levels of particulate matter with diameter smaller than 1 µm were observed in Dublin in November 2016 and January 2017 and can be attributed to emissions from residential burning of peat and wood, often promoted as ‘slow renewables’.

8 pages, 4 figures, Organic oligomers were discovered in laboratory-generated atmospheric aerosol over a decade ago. However, evidence for the presence of oligomers in ambient aerosols is scarce and mechanisms for their formation have yet to be fully elucidated. In this work, three unique aerosol particle types internally mixed with High molecular weight organic compounds (HMW-OC) species - likely oligomers - were detected in ambient air using single particle Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS) in Cork (Ireland) during winter 2009. These particle types can be described as follows: (1) HMW-OCs rich in organic nitrogen - possibly containing nitrocatechols and nitroguaiacols - originating from primary emissions of biomass burning particles during evening times; (2) HMW-OCs internally mixed with nitric acid, occurring in stagnant conditions during night time; and (3) HMW-OCs internally mixed with sea salt, likely formed via photochemical reactions during day time. The study exemplifies the power of methodologies capable of monitoring the simultaneous formation of organic and inorganic particle-phase reaction products. Primary emissions and atmospheric aging of different types of HMW-OC contributes to aerosol with a range of acidity, hygroscopic and optical properties, which can have different impacts on climate and health, This work was funded by the Ireland Higher Education Authority Programme for Research in Third Level Institutes (PRTL1) – Cycle 5, and the Irish Environmental Protection Agency. Additional founding by the Spanish Ministry of Economy through projects BIO-NUC (CGL2013-49020-R), and by the EU though the FP7-PEOPLE-2013-IOF programme (Project number 624680, MANU – Marine Aerosol NUcleations) and the Ramon y Cajal fellowship (RYC-2012-11922). The National Centre for Atmospheric Science NCAS Birmingham group is funded by the UK Natural Environment Research Council

In recent years, severe haze events often occurred in China, causing serious environmental problems. The mechanisms responsible for the haze formation, however, are still not well understood, hindering the forecast and mitigation of haze pollution. Our study of the 2012–13 winter haze events in Beijing shows that atmospheric water vapour plays a critical role in enhancing the heavy haze events. Under weak solar radiation and stagnant moist meteorological conditions in winter, air pollutants and water vapour accumulate in a shallow planetary boundary layer (PBL). A positive feedback cycle is triggered resulting in the formation of heavy haze: (1) the dispersal of water vapour is constrained by the shallow PBL, leading to an increase in relative humidity (RH); (2) the high RH induces an increase of aerosol particle size by enhanced hygroscopic growth and multiphase reactions to increase particle size and mass, which results in (3) further dimming and decrease of PBL height, and thus further depressing of aerosol and water vapour in a very shallow PBL. This positive feedback constitutes a self-amplification mechanism in which water vapour leads to a trapping and massive increase of particulate matter in the near-surface air to which people are exposed with severe health hazards.

An aerosol chemical speciation monitor (ACSM) was deployed to study the primary nonrefractory submicron particulate matter emissions from the burning of commercially available solid fuels (peat, coal, and wood) typically used in European domestic fuel stoves. Organic mass spectra (MS) from burning wood, peat, and coal were characterized and intercompared for factor analysis against ambient data. The reference profiles characterized in this study were used to estimate the contribution of solid fuel sources, along with oil combustion, to ambient pollution in Galway, Ireland using the multilinear engine (ME-2). During periods influenced by marine air masses, local source contribution had dominant impact and nonsea-spray primary organic emissions comprised 88% of total organic aerosol mass, with peat burning found to be the greatest contributor (39%), followed by oil (21%), coal (17%), and wood (11%). In contrast, the resolved oxygenated organic aerosol (OOA) dominated the aerosol composition in continental air masses, with contributions of 50%, compared to 12% in marine air masses. The source apportionment results suggest that the use of domestic solid fuels (peat, wood, and coal) for home heating is the major source of evening and night-time particulate pollution events despite their small use.

The importance of 3D winds (in particular updraft) in atmospheric science has motivated the adaptation of airborne wind instruments developed for manned aircraft, to the small size of Remotely Piloted Aircraft Systems (RPAS). Simultaneously, enhancements in RPAS technology have increased their contribution to many fields. In atmospheric research, lightweight RPAS (

Since the 1980's, measures mitigating the impact of transboundary air pollution have been implemented successfully as evidenced in the 1980-2014 record of atmospheric sulphur pollution over the NE-Atlantic, a key region for monitoring background northern-hemisphere pollution levels. The record reveals a 72-79% reduction in annual-average airborne sulphur pollution (SO4 and SO2, respectively) over the 35-year period. The NE-Atlantic, as observed from the Mace Head research station on the Irish coast, can be considered clean for 64% of the time during which sulphate dominates PM1 levels, contributing 42% of the mass, and for the remainder of the time, under polluted conditions, a carbonaceous (organic matter and Black Carbon) aerosol prevails, contributing 60% to 90% of the PM1 mass and exhibiting a trend whereby its contribution increases with increasing pollution levels. The carbonaceous aerosol is known to be diverse in source and nature and requires sophisticated air pollution policies underpinned by sophisticated characterisation and source apportionment capabilities to inform selective emissions-reduction strategies. Inauspiciously, however, this carbonaceous concoction is not measured in regulatory Air Quality networks. The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007–2013) project BACCHUS under grant agreement n°603445, the Irish Environmental Protection Agency, the HEA PRTLI4 project. peer-reviewed

Ice nucleating particles (INP) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. The atmospheric INP concentration changes by orders of magnitude from terrestrial to marine environments, which typically contain much lower concentrations. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference because they were developed based on measurements predominantly from terrestrial environments. Errors in the assumed INP concentration will influence the simulated amount of ice in mixed-phase clouds, leading to errors in top-of-atmosphere radiative flux and ultimately the climate sensitivity of climate models. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two-species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to neglect of INP from other terrestrial sources. Our model indicates that, on a monthly or yearly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important in the world's remote oceans and can dominate in the Southern Ocean at some time of the year. Furthermore, we show that day-to-day variability is important and since desert dust aerosol tends to be sporadic, marine organics dominate the INP population on many days per month in much of the mid and high latitude northern hemisphere. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INP in models, which will guide ice nucleation researchers on where to focus future laboratory and field work.

Over forty scientists from six countries convened in Raleigh, NC on June 4-6 2012 to review the status and prospects of sea spray aerosol research. Participants were researchers from the oceanography and atmospheric science communities, including academia, private industry, and government agencies. The recommendations from the working groups are summarized in a science prioritization matrix that is meant to prioritize the research agenda and identify areas of investigation by the magnitude of their impact on proposed science questions. Str

Based on the results of a pilot study in 2007, which found high mixing ratios of molecular iodine (I2) above the intertidal macroalgae (seaweed) beds at Mweenish Bay (Ireland), we extended the study to nine different locations in the vicinity of Mace Head Atmospheric Research Station on the west coast of Ireland during a field campaign in 2009. The mean values of I2 mixing ratio found above the macroalgae beds at nine different locations ranged from 104 to 393 ppt, implying a high source strength of I2. Such mixing ratios are sufficient to result in photochemically driven coastal new-particle formation events. Mixing ratios above the Ascophyllum nodosum and Fucus vesiculosus beds increased with exposure time: after 6 h exposure to ambient air the mixing ratios were one order of magnitude higher than those initially present. This contrasts with the emission characteristics of Laminaria digitata, where most I2 was emitted within the first half hour of exposure. Discrete in situ measurements (offline) of I2 emission from ambient air-exposed chamber experiments of L. digitata, A. nodosum and F. vesiculosus substantially supported the field observations. Further online and time-resolved measurements of the I2 emission from O3-exposed macroalgal experiments in a chamber confirmed the distinct I2 emission characteristics of A. nodosum and F. vesiculosus compared to those of L. digitata. The emission rates of A. nodosum and F. vesiculosus were comparable to or even higher than L. digitata after the initial exposure period of ~20–30 min. We suggest that A. nodosum and F. vesiculosus may provide an important source of photolabile iodine in the coastal boundary layer and that their impact on photochemistry and coastal new-particle formation should be reevaluated in light of their longer exposure at low tide and their widespread distribution.

[1] Initial efforts toward developing a combined organic-inorganic sea spray source function parameterization for large-scale models made use of chlorophyll-a (Chl-a) and wind speed as input parameters to combine oceanic biology and atmospheric dynamics. These studies reported a modest correlation coefficient (0.55) between chlorophyll-a and organic matter (OM) enrichment in sea spray, suggesting that chlorophyll-a is only partially suitable for predicting organic enrichment. A reconstructed chlorophyll-a field of the North Atlantic Ocean from GlobColour reveals an improved correlation of 0.72 between the fractional mass contribution of organics in sea spray and chlorophyll-a concentration. A similar analysis, using colored dissolved and detrital organic material absorption and particulate organic carbon concentration, revealed slightly lower correlation coefficients (0.65 and 0.68). These results indicate that to date, chlorophyll-a is the best biological surrogate for predicting sea spray organic enrichment. In fact, considering the minimal difference between the correlation coefficients obtained with the three ocean color products, there is no reason to substitute chlorophyll-a, which is the most accurate parameter obtained from ocean color data, with other biological surrogates being generally affected by larger and less known errors. The observed time lag between chlorophyll-a concentration and organic matter enrichment in aerosol suggests that biological processes in oceanic surface waters and their timescales should be considered when modeling the production of primary marine organic aerosol.

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the polar orbiter Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is an elastic backscatter lidar that produces a global uniformly-calibrated aerosol data set. Several Calibration/Validation (Cal/Val) studies for CALIOP conducted with ground-based lidars and CALIOP data showed large aerosol profile disagreements, both random and systematic. In an attempt to better understand these problems, we undertook a series of ground-based lidar measurements in Atlanta, Georgia, which did not provide better agreement with CALIOP data than the earlier efforts, but rather prompted us to investigate the statistical limitations of such comparisons. Meaningful Cal/Val requires intercomparison data sets with small enough uncertainties to provide a check on the maximum expected calibration error. For CALIOP total attenuated backscatter, reducing the noise to the required level requires averaging profiles along the ground track for distances of at least 1,500 km. Representative comparison profiles often cannot be acquired with ground-based lidars because spatial aerosol inhomogeneities introduce systematic error into the averages. These conclusions have implications for future satellite lidar Cal/Val efforts, because planned satellite lidars measuring aerosol backscatter, wind vector, and CO2 concentration profiles may all produce data requiring considerable along-track averaging for meaningful Cal/Val.

Highly time-resolved measurements of nitrous acid (HONO) were carried out with a highly sensitive long path absorption photometer (LOPAP) at an urban site of Xi'an in Western China from 24 July to 6 August 2015 to investigate the atmospheric variations, sources, and formation pathways of HONO. The concentrations of HONO vary from 0.02 to 4.3ppbv with an average of 1.12ppbv for the entire measurement period. The variation trends of HONO and NO2 are very similar and positively correlated which, together with the similar diurnal profiles of HONO/NO2 ratio and HONO, suggest the importance of heterogeneous conversion of HONO from NO2. The nocturnal HONO level is governed by heterogeneous formation from NO2, followed by homogeneous formation of NO with OH and then by direct emissions. Further, it is found that the heterogeneous formation of HONO is largely affected by relative humidity and aerosol surface. Daytime HONO budget analysis indicates that an additional unknown source with HONO production rate of 0.75ppbvh-1 is required to explain the observed HONO concentration, which contributes 60.8% of the observed daytime HONO.

International audience; We evaluated a modified VBS (volatility basis set) scheme to treat biomass-burning-like organic aerosol (BBOA) implemented in CAMx (Comprehensive Air Quality Model with extensions). The updated scheme was param-eterized with novel wood combustion smog chamber experiments using a hybrid VBS framework which accounts for a mixture of wood burning organic aerosol precursors and their further functionalization and fragmentation in the atmosphere. The new scheme was evaluated for one of the winter EMEP intensive campaigns (February-March 2009) against aerosol mass spectrometer (AMS) measurements performed at 11 sites in Europe. We found a considerable improvement for the modelled organic aerosol (OA) mass compared to our previous model application with the mean fractional bias (MFB) reduced from −61 to −29 %. We performed model-based source apportionment studies and compared results against positive matrix factorization (PMF) analysis performed on OA AMS data. Both model and observations suggest that OA was mainly of secondary origin at almost all sites. Modelled secondary organic aerosol (SOA) contributions to total OA varied from 32 to 88 % (with an average contribution of 62 %) and absolute concentrations were generally under-predicted. Modelled primary hydrocarbon-like organic aerosol (HOA) and primary biomass-burning-like aerosol (BBPOA) fractions contributed to a lesser extent (HOA from 3 to 30 %, and BBPOA from 1 to 39 %) with average contributions of 13 and 25 %, respectively. Modelled BBPOA fractions were found to represent 12 to 64 % of the total residential-heating-related OA, with increasing contributions at stations located in the northern part of the domain. Source apportionment studies were performed to assess the contribution of residential and non-residential combustion precursors to the total SOA. Non-residential combustion and road transportation sector contributed about 30-40 % to SOA formation (with increasing contributions at urban and near industrialized sites), whereas residential combustion (mainly related to wood burning) contributed to a larger extent, around 60-70 %. Contributions to OA from residential combustion precursors in different volatility ranges were Published by Copernicus Publications on behalf of the European Geosciences Union. 7654 G. Ciarelli et al.: Modelling winter organic aerosol at the European scale with CAMx also assessed: our results indicate that residential combustion gas-phase precursors in the semivolatile range (SVOC) contributed from 6 to 30 %, with higher contributions predicted at stations located in the southern part of the domain. On the other hand, the oxidation products of higher-volatility precursors (the sum of intermediate-volatility compounds (IVOCs) and volatile organic compounds (VOCs)) contribute from 15 to 38 % with no specific gradient among the stations. Although the new parameterization leads to a better agreement between model results and observations, it still under-predicts the SOA fraction, suggesting that uncertainties in the new scheme and other sources and/or formation mechanisms remain to be elucidated. Moreover, a more detailed characterization of the semivolatile components of the emissions is needed.

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.

Currently many ground-based atmospheric stations include in-situ measurements of aerosol physical and optical properties, resulting in more than 20 long-term (> 10 yr) aerosol measurement sites in the Northern Hemisphere and Antarctica. Most of these sites are located at remote locations and monitor the aerosol particle number concentration, wavelength-dependent light scattering, backscattering, and absorption coefficients. The existence of these multi-year datasets enables the analysis of long-term trends of these aerosol parameters, and of the derived light scattering Ångström exponent and backscatter fraction. Since the aerosol variables are not normally distributed, three different methods (the seasonal Mann-Kendall test associated with the Sen's slope, the generalized least squares fit associated with an autoregressive bootstrap algorithm for confidence intervals, and the least-mean square fit applied to logarithms of the data) were applied to detect the long-term trends and their magnitudes. To allow a comparison among measurement sites, trends on the most recent 10 and 15 yr periods were calculated. No significant trends were found for the three continental European sites. Statistically significant trends were found for the two European marine sites but the signs of the trends varied with aerosol property and location. Statistically significant decreasing trends for both scattering and absorption coefficients (mean slope of −2.0% yr−1) were found for most North American stations, although positive trends were found for a few desert and high-altitude sites. The difference in the timing of emission reduction policy for the Europe and US continents is a likely explanation for the decreasing trends in aerosol optical parameters found for most American sites compared to the lack of trends observed in Europe. No significant trends in scattering coefficient were found for the Arctic or Antarctic stations, whereas the Arctic station had a negative trend in absorption coefficient. The high altitude Pacific island station of Mauna Loa presents positive trends for both scattering and absorption coefficients.

A regional climate model is used to assess changes in atmospheric ozone for the years 2030, 2050 and 2100 relative to 2006 brought about by changes in meteorology and emissions. The simulations are evaluated against ozone measurements for 2006, exhibiting good agreement between the model-predicted measurements and the measured annual cycles. Under the RCP6 emission scenario used in these simulations, average ozone mixing ratios are set to reduce by 2.0 ppb over domains encompassing Europe and the North East Atlantic between 2006 and 2100 with the most significant decrease occurring after 2050 due to the pattern in changing emissions. Peak reductions of more than 8 ppb are observed during summer time over mainland Europe by 2100. Model output was studied for three relevant sub-domains, namely the North East Atlantic, Ireland and Europe. The relative contribution of changes in both emissions and meteorology is assessed. Over the whole domain, changing emissions are predominantly responsible for changes in surface ozone; although over the North East Atlantic domain, the changing emissions do not perturb surface ozone trends and the decrease in 2100 levels is entirely attributable to changing meteorology.

Many of the next generation of global climate models will include aerosol schemes which explicitly simulate the microphysical processes that determine the particle size distribution. These models enable aerosol optical properties and cloud condensation nuclei (CCN) concentrations to be determined by fundamental aerosol processes, which should lead to a more physically based simulation of aerosol direct and indirect radiative forcings. This study examines the global variation in particle size distribution simulated by twelve global aerosol microphysics models to quantify model diversity and to identify any common biases against observations. Evaluation against size distribution measurements from a new European network of aerosol supersites shows that the mean model agrees quite well with the observations at many sites on the annual mean, but there are some seasonal biases common to many sites. In particular, at many of these European sites, the accumulation mode number concentration is biased low during winter and Aitken mode concentrations tend to be overestimated in winter and underestimated in summer. At high northern latitudes, the models strongly underpredict Aitken and accumulation particle concentrations compared to the measurements, consistent with previous studies that have highlighted the poor performance of global aerosol models in the Arctic. In the marine boundary layer, the models capture the observed meridional variation in the size distribution, which is dominated by the Aitken mode at high latitudes, with an increasing concentration of accumulation particles with decreasing latitude. Considering vertical profiles, the models reproduce the observed peak in total particle concentrations in the upper troposphere due to new particle formation, although modelled peak concentrations tend to be biased high over Europe. Overall, the multi-model-mean dataset simulates the global variation of the particle size distribution with a good degree of skill, suggesting that most of the individual global aerosol microphysics models are performing well, although the large model diversity indicates that some models are in poor agreement with the observations. Further work is required to better constrain size-resolved primary and secondary particle number sources, and an improved understanding of nucleation and growth (e.g. the role of nitrate and secondary organics) will improve the fidelity of simulated particle size distributions.

Stable carbon isotope ratios in marine aerosol collected over the Southern Indian Ocean revealed δ13C values ranging from −20.0‰ to −28.2‰. The isotope ratios exhibited a strong correlation with the fractional organic matter (OM) enrichment in sea spray aerosol. The base-level isotope ratio of −20.0‰ is characteristic of an aged Dissolved Organic Matter (DOM) pool contributing a relatively homogeneous background level of DOM to oceanic waters. The range of isotope ratios, extending down to −28.2‰, is characteristic of more variable, stronger, and fresher Particulate Organic Matter (POM) pool driven by trophic level interactions. We present a conceptual dual-pool POM-DOM model which comprises a ‘young’ and variable POM pool which dominates enrichment in sea-spray and an ‘aged’ but invariant DOM pool which is, ultimately, an aged end-product of processed ‘fresh’ POM. This model is harmonious with the preferential enrichment of fresh colloidal and nano-gel lipid-like particulate matter in sea spray particles and the observed depleted δ13C ratio resulting from isotope equilibrium fractionation coupled with enhanced plankton photosynthesis in cold water (−2 °C to +8 °C). These results re-assert the hypothesis that OM enrichment in sea-spray is directly linked to primary production and, consequently, can have implications for climate-aerosol-cloud feedback systems.

Homogeneous nucleation and subsequent cluster growth leads to the formation of new aerosol particles in the atmosphere(1). The nucleation of sulfuric acid and organic vapours is thought to be responsible for the formation of new particles over continents(1,2), whereas iodine oxide vapours have been implicated in particle formation over coastal regions(3-7). The molecular clustering pathways that are involved in atmospheric particle formation have been elucidated in controlled laboratory studies of chemically simple systems(2,8-10), but direct molecular-level observations of nucleation in atmospheric field conditions that involve sulfuric acid, organic or iodine oxide vapours have yet to be reported(11). Here we present field data from Mace Head, Ireland, and supporting data from northern Greenland and Queen Maud Land, Antarctica, that enable us to identify the molecular steps involved in new particle formation in an iodine-rich, coastal atmospheric environment. We find that the formation and initial growth process is almost exclusively driven by iodine oxoacids and iodine oxide vapours, with average oxygen-to-iodine ratios of 2.4 found in the clusters. On the basis of this high ratio, together with the high concentrations of iodic acid (HIO3) observed, we suggest that cluster formation primarily proceeds by sequential addition of HIO3, followed by intracluster restructuring to I2O5 and recycling of water either in the atmosphere or on dehydration. Our study provides ambient atmospheric molecular-level observations of nucleation, supporting the previously suggested role of iodine-containing species in the formation of new aerosol particles(3-7,12-18), and identifies the key nucleating compound.

International audience; In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.

The third intensive measurement period (IMP) organised by the European Monitoring and Evaluation Programme (EMEP) under the UNECE CLTRAP took place in summer 2012 and winter 2013, with PM10 filter samples concurrently collected at 20 (16 EMEP) regional background sites across Europe for subsequent analysis of their mineral dust content. All samples were analysed by the same or a comparable methodology. Higher PM10 mineral dust loadings were observed at most sites in summer (0.5–10 µg m−3) compared to winter (0.2–2 µg m−3), with the most elevated concentrations in the southern- and easternmost countries, accounting for 20–40 % of PM10. Saharan dust outbreaks were responsible for the high summer dust loadings at western and central European sites, whereas regional or local sources explained the elevated concentrations observed at eastern sites. The eastern Mediterranean sites experienced elevated levels due to African dust outbreaks during both summer and winter. The mineral dust composition varied more in winter than in summer, with a higher relative contribution of anthropogenic dust during the former period. A relatively high contribution of K from non-mineral and non-sea-salt sources, such as biomass burning, was evident in winter at some of the central and eastern European sites. The spatial distribution of some components and metals reveals the influence of specific anthropogenic sources on a regional scale: shipping emissions (V, Ni, and SO42−) in the Mediterranean region, metallurgy (Cr, Ni, and Mn) in central and eastern Europe, high temperature processes (As, Pb, and SO42−) in eastern countries, and traffic (Cu) at sites affected by emissions from nearby cities.

Multigenerational oxidation chemistry of atmospheric organic compounds and its effects on aerosol loadings and chemical composition is investigated by implementing the Two-Dimensional Volatility Basis Set (2-D-VBS) in a Lagrangian host chemical transport model. Three model formulations were chosen to explore the complex interactions between functionalization and fragmentation processes during gas-phase oxidation of organic compounds by the hydroxyl radical. The base case model employs a conservative transformation by assuming a reduction of one order of magnitude in effective saturation concentration and an increase of oxygen content by one or two oxygen atoms per oxidation generation. A second scheme simulates functionalization in more detail using group contribution theory to estimate the effects of oxygen addition to the carbon backbone on the compound volatility. Finally, a fragmentation scheme is added to the detailed functionalization scheme to create a functionalization-fragmentation parameterization. Two condensed-phase chemistry pathways are also implemented as additional sensitivity tests to simulate (1) heterogeneous oxidation via OH uptake to the particle-phase and (2) aqueous-phase chemistry of glyoxal and methylglyoxal. The model is applied to summer and winter periods at three sites where observations of organic aerosol (OA) mass and O:C were obtained during the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) campaigns. The base case model reproduces observed mass concentrations and O:C well, with fractional errors (FE) lower than 55% and 25%, respectively. The detailed functionalization scheme tends to overpredict OA concentrations, especially in the summertime, and also underpredicts O:C by approximately a factor of 2. The detailed functionalization model with fragmentation agrees well with the observations for OA concentration, but still underpredicts O:C. Both heterogeneous oxidation and aqueous-phase processing have small effects on OA levels but heterogeneous oxidation, as implemented here, does enhance O:C by about 0.1. The different schemes result in very different fractional attribution for OA between anthropogenic and biogenic sources.

Aerosol loading in the marine environment is investigated using aerosol composition measurements from several research ship campaigns (ICEALOT, MAP, RHaMBLe, VOCALS and OOMPH), observations of total AOD column from satellite (MODIS) and ship-based instruments (Maritime Aerosol Network, MAN), and a global chemical transport model (GEOS-Chem). This work represents the most comprehensive evaluation of oceanic OM emission inventories to date, by employing aerosol composition measurements obtained from campaigns with wide spatial and temporal coverage. The model underestimates AOD over the remote ocean on average by 0.02 (21 %), compared to satellite observations, but provides an unbiased simulation of ground-based Maritime Aerosol Network (MAN) observations. Comparison with cruise data demonstrates that the GEOS-Chem simulation of marine sulfate, with the mean observed values ranging between 0.22 μg m−3 and 1.34 μg m−3, is generally unbiased, however surface organic matter (OM) concentrations, with the mean observed concentrations between 0.07 μg m−3 and 0.77 μg m−3, are underestimated by a factor of 2–5 for the standard model run. Addition of a sub-micron marine OM source of approximately 9 TgC yr−1 brings the model into agreement with the ship-based measurements, however this additional OM source does not explain the model underestimate of marine AOD. The model underestimate of marine AOD is therefore likely the result of a combination of satellite retrieval bias and a missing marine aerosol source (which exhibits a different spatial pattern than existing aerosol in the model).