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A reliable assessment of the optical properties of atmospheric black carbon is of crucial importance for an accurate estimation of radiative forcing. In this study we investigated the spatio-temporal variability of the mass absorption cross-section (MAC) of atmospheric black carbon, defined as light absorption coefficient (σap) divided by elemental carbon mass concentration (mEC). σap and mEC have been monitored at supersites of the ACTRIS network for a minimum period of one year. The 9 rural background sites considered in this study cover southern Scandinavia, central Europe and the Mediterranean. σap was determined using filter based absorption photometers and mEC using a thermal-optical technique. Homogeneity of the data-set was ensured by harmonization of all involved methods and instruments during extensive intercomparison exercises at the European Center for Aerosol Calibration (ECAC). Annual mean values of σap at a wavelength of 637 nm vary between 0.66 and 1.3 Mm−1 in southern Scandinavia, 3.7–11 Mm−1 in Central Europe and the British Isles, and 2.3–2.8 Mm−1 in the Mediterranean. Annual mean values of mEC vary between 0.084 and 0.23 μg m−3 in southern Scandinavia, 0.28–1.1 in Central Europe and the British Isles, and 0.22–0.26 in the Mediterranean. Both σap and mEC in southern Scandinavia and Central Europe have a distinct seasonality with maxima during the cold season and minima during summer, whereas at the Mediterranean sites an opposite trend was observed. Annual mean MAC values were quite similar across all sites and the seasonal variability was small at most sites. Consequently, a MAC value of 10.0 m2 g−1 (geometric standard deviation = 1.33) at a wavelength of 637 nm can be considered to be representative of the mixed boundary layer at European background sites, where BC is expected to be internally mixed to a large extent. The observed spatial variability is rather small compared to the variability of values in previous literature, indicating that the harmonization efforts resulted in substantially increased precision of the reported MAC. However, absolute uncertainties of the reported MAC values remain as high as ± 30–70% due to the lack of appropriate reference methods and calibration materials. The mass ratio between elemental carbon and non-light-absorbing matter was used as a proxy for the thickness of coatings around the BC cores, in order to assess the influence of the mixing state on the MAC of BC. Indeed, the MAC was found to increase with increasing values of the coating thickness proxy. This provides evidence that coatings do increase the MAC of atmospheric BC to some extent, which is commonly referred to as lensing effect. © 2016 The Authors, The research leading to these results has received funding from the European Union Seventh Framework Programme (ACTRIS, FP7/2007-2013, grant agreement no. 262254 ). ACTRIS-2 is a European Project supported by the European Commission Horizon 2020 Research and Innovation Framework Programme (ACTRIS-2, H2020-INFRAIA-2014-2015, grant agreement no. 654109 ). This work was also supported by grants from Labex OSUG@2020 (PhD investissements d'avenir – ANR10 LABX56) and from the European Research Council (ERC-CoG 615922-BLACARAT). Appendix A.

Sea salt aerosol (SSA) is one of the major components of primary aerosols and has significant impact on the formation of secondary inorganic particles mass on a global scale. In this study, the fully online coupled WRF-Chem model was utilized to evaluate the SSA emission scheme and its influence on the nitrate simulation in a case study in Europe during 10–20 September 2013. Meteorological conditions near the surface, wind pattern and thermal stratification structure were well reproduced by the model. Nonetheless, the coarse-mode (PM1 − 10) particle mass concentration was substantially overestimated due to the overestimation of SSA and nitrate. Compared to filter measurements at four EMEP stations (coastal stations: Bilthoven, Kollumerwaard and Vredepeel; inland station: Melpitz), the model overestimated SSA concentrations by a factor of 8–20. We found that this overestimation was mainly caused by overestimated SSA emissions over the North Sea during 16–20 September. Over the coastal regions, SSA was injected into the continental free troposphere through an “aloft bridge” (about 500 to 1000 m above the ground), a result of the different thermodynamic properties and planetary boundary layer (PBL) structure between continental and marine regions. The injected SSA was further transported inland and mixed downward to the surface through downdraft and PBL turbulence. This process extended the influence of SSA to a larger downwind region, leading, for example, to an overestimation of SSA at Melpitz, Germany, by a factor of ∼ 20. As a result, the nitrate partitioning fraction (ratio between particulate nitrate and the summation of particulate nitrate and gas-phase nitric acid) increased by about 20 % for the coarse-mode nitrate due to the overestimation of SSA at Melpitz. However, no significant difference in the partitioning fraction for the fine-mode nitrate was found. About 140 % overestimation of the coarse-mode nitrate resulted from the influence of SSA at Melpitz. In contrast, the overestimation of SSA inhibited the nitrate particle formation in the fine mode by about 20 % because of the increased consumption of precursor by coarse-mode nitrate formation.

Laboratory experiments suggest that water-soluble products from the gas-phase oxidation of volatile organic compounds can partition into atmospheric waters where they are further oxidized to form low volatility products, providing an alternative route for oxidation in addition to further oxidation in the gas phase. These products can remain in the particle phase after water evaporation, forming what is termed as aqueous secondary organic aerosol (aqSOA). However, few studies have attempted to observe ambient aqSOA. Therefore, a suite of measurements, including near-real-time WSOC (water-soluble organic carbon), inorganic anions/cations, organic acids, and gas-phase glyoxal, were made during the PEGASOS (Pan-European Gas-AeroSOls-climate interaction Study) 2012 campaign in the Po Valley, Italy, to search for evidence of aqSOA. Our analysis focused on four periods: Period A on 19–21 June, Period B on 30 June and 1–2 July, Period C on 3–5 July, and Period D on 6–7 July to represent the first (Period A) and second (Periods B, C, and D) halves of the study. These periods were picked to cover varying levels of WSOC and aerosol liquid water. In addition, back trajectory analysis suggested all sites sampled similar air masses on a given day. The data collected during both periods were divided into times of increasing relative humidity (RH) and decreasing RH, with the aim of diminishing the influence of dilution and mixing on SOA concentrations and other measured variables. Evidence for local aqSOA formation was only observed during Period A. When this occurred, there was a correlation of WSOC with organic aerosol (R2 = 0.84), aerosol liquid water (R2 = 0.65), RH (R2 = 0.39), and aerosol nitrate (R2 = 0.66). Additionally, this was only observed during times of increasing RH, which coincided with dark conditions. Comparisons of WSOC with oxygenated organic aerosol (OOA) factors, determined from application of positive matrix factorization analysis on the aerosol mass spectrometer observations of the submicron non-refractory organic particle composition, suggested that the WSOC differed in the two halves of the study (Period A WSOC vs. OOA-2 R2 = 0.83 and OOA-4 R2 = 0.04, whereas Period C WSOC vs. OOA-2 R2 = 0.03 and OOA-4 R2 = 0.64). OOA-2 had a high O ∕ C (oxygen ∕ carbon) ratio of 0.77, providing evidence that aqueous processing was occurring during Period A. Key factors of local aqSOA production during Period A appear to include air mass stagnation, which allows aqSOA precursors to accumulate in the region; the formation of substantial local particulate nitrate during the overnight hours, which enhances water uptake by the aerosol; and the presence of significant amounts of ammonia, which may contribute to ammonium nitrate formation and subsequent water uptake and/or play a more direct role in the aqSOA chemistry.

The particle number size distribution is an important parameter to characterize the atmospheric aerosol and its influence on the Earth's climate. Here we describe a new Optical Particle Size Spectrometer (OPSS) for measurements of the accumulation mode particle number size distribution in the tropopause region onboard a passenger aircraft (IAGOS-CARIBIC observatory (In-service Aircraft for a Global Observing System – Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container)). A modified "KS93 particle sensor" from RION Co., Ltd. together with a new airflow system and a dedicated data acquisition system are the key components of the CARIBIC OPSS. The instrument records individual particle pulses in the particle size range 130–1110 nm diameter (for a particle refractive index of 1.47-i0.006 for an upper tropospheric (UT) aerosol particle) and thus allows the post-flight choice of the time resolution and the size distribution bin width. The CARIBIC OPSS has a 50 % particle detection diameter of 152 nm and a maximum asymptotic counting efficiency of 98 %. The instruments measurement performance shows no pressure dependency and no coincidence for free tropospheric conditions. The size response function of the CARIBIC OPSS was obtained by a polystyrene latex calibration in combination with model calculations. Particle number size distributions measured with the new OPSS in the lowermost stratosphere agreed within a factor of two in concentration with balloon-borne measurements over western North America. Since June 2010 the CARIBIC OPSS is deployed once per month in the IAGOS-CARIBIC observatory.

Cloud optical properties in the trade winds over the eastern Caribbean Sea have been shown to be sensitive to cloud condensation nuclei (CCN) concentrations. The objective of the current study was to investigate the CCN properties in the marine boundary layer (MBL) in the tropical western North Atlantic, in order to assess the respective roles of inorganic sulfate, organic species, long-range transported mineral dust and sea-salt particles. Measurements were carried out in June–July 2013, on the east coast of Barbados, and included CCN number concentrations, particle number size distributions and offline analysis of sampled particulate matter (PM) and sampled accumulation mode particles for an investigation of composition and mixing state with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX). During most of the campaign, significant mass concentrations of long-range transported mineral dust was present in the PM, and influence from local island sources can be ruled out. The CCN and particle number concentrations were similar to what can be expected in pristine marine environments. The hygroscopicity parameter κ was inferred, and values in the range 0.2–0.5 were found during most of the campaign, with similar values for the Aitken and the accumulation mode. The accumulation mode particles studied with TEM were dominated by non-refractory material, and concentrations of mineral dust, sea salt and soot were too small to influence the CCN properties. It is highly likely that the CCN were dominated by a mixture of sulfate species and organic compounds.

Elemental Carbon (EC) has a significant impact on human health and climate change. In order to evaluate the size segregation of EC emission in the EUCAARI inventory and investigate its influence on the simulation of EC long-range transportation in Europe, we used the fully coupled online Weather Research and Forecasting/Chemistry model (WRF-Chem) at a resolution of 2 km focusing on a region in Germany, in conjunction with a high-resolution EC emission inventory. The ground meteorology conditions, vertical structure and wind pattern were well reproduced by the model. The simulations of particle number and/or mass size distributions were evaluated with observations at the central European background site Melpitz. The fine mode particle concentration was reasonably well simulated, but the coarse mode was substantially overestimated by the model mainly due to the plume with high EC concentration in coarse mode emitted by a nearby point source. The comparisons between simulated EC and Multi-angle Absorption Photometers (MAAP) measurements at Melpitz, Leipzig-TROPOS and Bösel indicated that the coarse mode EC (ECc) emitted from the nearby point sources might be overestimated by a factor of 2–10. The fraction of ECc was overestimated in the emission inventory by about 10–30 % for Russia and 5–10 % for Eastern Europe (e.g., Poland and Belarus). This incorrect size-dependent EC emission results in a shorter atmospheric life time of EC particles and inhibits the long-range transport of EC. A case study showed that this effect caused an underestimation of 20–40 % in the EC mass concentration in Germany under eastern wind pattern.

In this investigation, we summarize performance parameters of 24 TSI CPCs model 3772 and 9 TSI CPCs model 3790 determined at the World Calibration Aerosol Centre Physics hosted by the Leibniz Institute for Tropospheric Research. Model 3790 CPCs are basically identical to model 3772 laminar continuous flow type butanol-based CPCs with a modified temperature difference between saturator and condenser. The average 50% detection efficiency for silver particles for 3772 and 3790 instruments was found to be 7.52 ± 0.04 nm and 24.34 ± 0.29 nm (average mobility diameter ± standard deviation), respectively. Small changes of the temperature difference between saturator and condenser cause larger shifts of the 50% detection efficiencies of 3790 CPCs compared to 3772 CPCs. In addition to the known calibration material dependence of the 50% detection efficiencies of 3790 CPCs, we found a dependence on the morphology of the particles used for calibration. In our experiments more spherical particles shifted the ...

As part of the European ACTRIS project, the first large Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) intercomparison study was conducted in the region of Paris for 3 weeks during the late-fall - early-winter period (November-December 2013). The first week was dedicated to the tuning and calibration of each instrument, whereas the second and third were dedicated to side-by-side comparison in ambient conditions with co-located instruments providing independent information on submicron aerosol optical, physical, and chemical properties. Near real-time measurements of the major chemical species (organic matter, sulfate, nitrate, ammonium, and chloride) in the non-refractory submicron aerosols (NR-PM1) were obtained here from 13 Q-ACSM. The results show that these instruments can produce highly comparable and robust measurements of the NR-PM1 total mass and its major components. Taking the median of the 13 Q-ACSM as a reference for this study, strong correlations (r2 > 0.9) were observed systematically for each individual Q-ACSM across all chemical families except for chloride for which three Q-ACSMs showing weak correlations partly due to the very low concentrations during the study. Reproducibility expanded uncertainties of Q-ACSM concentration measurements were determined using appropriate methodologies defined by the International Standard Organization (ISO 17025, 1999) and were found to be 9, 15, 19, 28, and 36 % for NR-PM1, nitrate, organic matter, sulfate, and ammonium, respectively. However, discrepancies were observed in the relative concentrations of the constituent mass fragments for each chemical component. In particular, significant differences were observed for the organic fragment at mass-to-charge ratio 44, which is a key parameter describing the oxidation state of organic aerosol. Following this first major intercomparison exercise of a large number of Q-ACSMs, detailed intercomparison results are presented, along with a discussion of some recommendations about best calibration practices, standardized data processing, and data treatment.

A comprehensive air quality study has been carried out at two urban background sites in Annaberg-Buchholz (Germany) and Usti nad Labem (Czech Republic) in the German–Czech border region between January 2012 and June 2014. Special attention was paid to quantify harmful fractions of particulate matter (PM) and ultrafine particle number concentration (UFP) from solid fuel combustion and vehicular traffic. Source type contributions of UFP were quantified by using the daily concentration courses of UFP and nitrogen oxide. Two different source apportionment techniques were used to quantify relative and absolute mass contributions: positive matrix factorization for total PM2.5 and elemental carbon in PM2.5 and chemical mass balance for total PM1 and organic carbon in PM1. Contributions from solid fuel combustion strongly differed between the non-heating period (April–September) and the heating period (October–March). Major sources of solid fuel combustion in this study were wood and domestic coal combustion, while the proportion of industrial coal combustion was low (

Quantification of the exposure of urban residents to ultrafine particle number concentrations (UFP) is challenging due to its high spatial and temporal variability. Hence, statistical models, e.g. generalized additive models (GAM), may be used to estimate time series or spatial characteristics of UFP. The GAM approach allows the representation of non-linear relations of a response variable with explanatory variables without the need to pre-define model functions. Up to now, GAMs were usually fitted to UFP data from a single site or from mobile measurement campaigns with limited temporal coverage. In this study, GAMs were used to determine UFP, accumulation mode particle (ACC) and total number concentration (TNC) at five urban sites in the cities of Leipzig and Dresden, Germany for the period 2011–2013. As explanatory variables, reanalysis data sets of meteorological quantities, urban geometry and traffic volume data were evaluated. Variables causing concurvity, which is the equivalent to collinearity in non-linear model approaches, were neglected to guarantee the interpretability of the final models. The models were then validated in a ten-fold cross-validation approach. The final models contained smooth functions for the building surface fraction, planetary boundary layer height, traffic volume, air temperature, wind direction, atmospheric pressure, relative humidity, global radiation and precipitation. Adjusted coefficients of determination (R2adj.) for the final models were R2adj. = 0.44 for UFP, R2adj. = 0.51 for ACC and R2adj. = 0.48 for TNC. Coefficients of determination of the cross-validation were in a similar range (0.44 for UFP, 0.51 for ACC, 0.49 for TNC). Finally, our study shows that GAMs are able to represent important processes that contribute to the particle number concentration from the smooth functions, i.e. emission, dilution, nucleation, deposition and long-range transport.

Recent studies demonstrate that Black Carbon (BC) pollution in economically developing megacities remain higher than the values, which the World Health Organization considers to be safe. Despite the scientific evidence of the degrees of BC exposure, there is still a lack of understanding on how the severe levels of BC pollution affect human health in these regions. We consider information on the respiratory tract deposition dose (DD) of BC to be essential in understanding the link between personal exposure to air pollutants and corresponding health effects. In this work, we combine data on fine and ultrafine refractory particle number concentrations (BC proxy), and activity patterns to derive the respiratory tract deposited amounts of BC particles for the population of the highly polluted metropolitan area of Manila, Philippines. We calculated the total DD of refractory particles based on three metrics: refractory particle number, surface area, and mass concentrations. The calculated DD of total refractory particle number in Metro Manila was found to be 1.6 to 17 times higher than average values reported from Europe and the U.S. In the case of Manila, ultrafine particles smaller than 100 nm accounted for more than 90% of the total deposited refractory particle dose in terms of particle number. This work is a first attempt to quantitatively evaluate the DD of refractory particles and raise awareness in assessing pollution-related health effects in developing megacities. We demonstrate that the majority of the population may be highly affected by BC pollution, which is known to have negative health outcomes if no actions are taken to mitigate its emission. For the governments of such metropolitan areas, we suggest to revise currently existing environmental legislation, raise public awareness, and to establish supplementary monitoring of black carbon in parallel to already existing PM10 and PM2.5 measures.

Atmospheric new particle formation (NPF) is an important phenomenon in terms of global particle number concentrations. Here we investigated the frequency of NPF, formation rates of 10 nm particles, and growth rates in the size range of 10–25 nm using at least 1 year of aerosol number size-distribution observations at 36 different locations around the world. The majority of these measurement sites are in the Northern Hemisphere. We found that the NPF frequency has a strong seasonal variability. At the measurement sites analyzed in this study, NPF occurs most frequently in March–May (on about 30% of the days) and least frequently in December–February (about 10% of the days). The median formation rate of 10 nm particles varies by about 3 orders of magnitude (0.01–10 cm􀀀3 s􀀀1) and the growth rate by about an order of magnitude (1–10 nm h􀀀1). The smallest values of both formation and growth rates were observed at polar sites and the largest ones in urban environments or anthropogenically influenced rural sites. The correlation between the NPF event frequency and the particle formation and growth rate was at best moderate among the different measurement sites, as well as among the sites belonging to a certain environmental regime. For a better understanding of atmospheric NPF and its regional importance, we would need more observational data from different urban areas in practically all parts of the world, from additional remote and rural locations in North America, Asia, and most of the Southern Hemisphere (especially Australia), from polar areas, and from at least a few locations over the oceans.

The present study is based on hourly aerosol particle and ancillary data taken at three stations in Northeastern Germany 150–200 km apart in the years 2009 through 2015 in order to investigate systematic process related differences that might show up when connecting their data with forward and backward air mass trajectories. The analysis of changes in the atmospheric aerosol during air mass transport between the stations focused on two low-pollution-to-high-pollution pathways of similar distance around 200 km. Despite rather different initial size distributions the increases in total concentration of particle number, volume, and black carbon agreed within 15%. Systematic variations were found in the different concentration increases as a function of time of day at which an interstation air mass transport took place that could be explained with related source and transport processes. With Radar-based precipitation data at the stations and along connecting trajectories sub-cloud particle scavenging was investigated. At each station sub-cloud particle scavenging coefficients were determined as a function of particle size between 10 and 700 nm diameter, and as a function of precipitation sums. Median particle scavenging coefficients taken over the central part of the size range of the study strongly increased between 0.2 and 1mm of precipitation and then planed out towards higher precipitation values. With the particle scavenging coefficients determined at the individual stations and precipitation data along connecting trajectories the sub-cloud particle scavenging analysis was extended to wet scavenging along the transport paths yielding median sub-cloud scavenging ratios over the range 0.2–25mm of precipitation sums with a non-linear shape similar to that of the median particle scavenging coefficients at the individual stations. Whereas in light precipitation more than 80% of the initial particles in the considered range survived 150–200 km of transport, more than 50% was scavenged by more than 15mm of precipitation during aerosol transport.

Background The link between concentrations of particulate matter (PM) and respiratory morbidity has been investigated in numerous studies. Objectives The aim of this study was to analyze the role of different particle size fractions with respect to respiratory health in Beijing, China. Methods Data on particle size distributions from 3 nm to 1 μm; PM10 (PM ≤ 10 μm), nitrogen dioxide (NO2), and sulfur dioxide concentrations; and meteorologic variables were collected daily from March 2004 to December 2006. Concurrently, daily counts of emergency room visits (ERV) for respiratory diseases were obtained from the Peking University Third Hospital. We estimated pollutant effects in single- and two-pollutant generalized additive models, controlling for meteorologic and other time-varying covariates. Time-delayed associations were estimated using polynomial distributed lag, cumulative effects, and single lag models. Results Associations of respiratory ERV with NO2 concentrations and 100–1,000 nm particle number or surface area concentrations were of similar magnitude—that is, approximately 5% increase in respiratory ERV with an interquartile range increase in air pollution concentration. In general, particles < 50 nm were not positively associated with ERV, whereas particles 50–100 nm were adversely associated with respiratory ERV, both being fractions of ultrafine particles. Effect estimates from two-pollutant models were most consistent for NO2. Conclusions Present levels of air pollution in Beijing were adversely associated with respiratory ERV. NO2 concentrations seemed to be a better surrogate for evaluating overall respiratory health effects of ambient air pollution than PM10 or particle number concentrations in Beijing.

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.

The marine aerosol is one of the most important natural aerosol systems and can significantly impact the global climate as well as biological cycle. A series of measurements during four open-ocean cruises in 2011 and 2012 over the Atlantic from 53° N to 53° S were conducted to reveal the physical and chemical properties of the marine boundary layer (MBL) aerosol and its seasonality. Chemical composition of the submicron particles was obtained using the on-line techniques High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) as well as from offline high-volume PM1 filter samples with a sampling time of 24 hours. Our measurements show that the MBL aerosol particle mass is controlled by sulfate (50 %), followed by organics (21 %), sea salt (12 %), ammonium (9 %), Black Carbon (BC, 5 %) and nitrate (3 %). Only sulfate exhibits pronouncedly seasonal dependency, while no such trend was observed in other species. Source apportionment of the organic fraction was performed using Positive Matrix Factorization (PMF). Five factors were identified, including three marine sources and two non-marine sources. Marine sources are linked to primary production (19 % of total organic aerosol (OA) mass), marine dimethylsulfide (DMS)-oxidation (16 %), and amine-related secondary formation (16 %). The other two OA components are attributed to continental outflow (19 %) and aged ship exhausts – biomass burning emissions (30 %). Our study indicates that, on average, non-marine sources nearly have the equal importance to the Atlantic aerosols comparing with the marine sources, respectively contributing 49 % and 51 % to the total OA mass loadings. The South Atlantic atmosphere is found to be less polluted than the North according to our source analysis. Detailed latitudinal distribution of OA sources showed that DMS oxidation contributes remarkably to the MBL aerosol over the South Atlantic during spring, while continental pollutants largely contaminate the marine atmosphere when near the west and middle Africa (15° N~15° S) as well as Europe. Based on our measurements, SOA produced from DMS oxidation over the Atlantic can be estimated as MSA mass concentration times a scaling factor 1.79 for spring season, which is derived from the strong correlation (R2 > 0.85) between MSA and DMS-oxidation OA component.

This study presents vertical profiles up to a height of 2300 m a.s.l. of aerosol microphysical and optical properties and cloud condensation nuclei (CCN). Corresponding data have been measured during a field campaign as part of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiments (HOPE), which took place at Melpitz, Germany from September 9 to 29, 2013. The helicopter-borne payload ACTOS (Airborne Cloud and Turbulence Observation System) was used to determine the aerosol particle number size distribution (PNSD), the number concentrations of aerosol particles (PNC) and cloud condensation nuclei (CCN) (CCN-NC), the ambient relative humidity (RH), and temperature (T). Simultaneous measurements on ground provided a holistic view on aerosol microphysical properties such as the PNSD, the chemical composition and the CCN-NC. Additional measurements of a 3 + 2 wavelength polarization lidar system (PollyXT) provided profiles of the aerosol particle light backscatter coefficient (σbsc) for three wavelengths (355, 532 and 1064 nm). From profiles of σbsc profiles of the aerosol particle light extinction coefficient (σext) were determined using the extinction-to-backscatter ratio. Furthermore, CCN-NC profiles were estimated on basis of the lidar-measurements. Ambient state optical properties of aerosol particles were derived on the basis of airborne in situ measurements of ACTOS (PNSD) and in situ measurements on ground (chemical aerosol characterization) using Mie-theory. On the basis of ground-based and airborne measurements, this work investigates the representativeness of ground-based aerosol microphysical properties for the boundary layer for two case-studies. The PNSD measurements on ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative for the PBL when the PBL is well mixed. Locally isolated new particle formation events on ground or at the top of the PBL led to vertical variability in the here presented cases and ground-based measurements are not representative for the PBL. Furthermore, the lidar-based estimates of CCN-NC profiles were compared with the airborne in situ measurements of ACTOS. This comparison showed good agreements within the uncertainty range. Finally, this work provides a closure study between the optical aerosol particle properties in ambient state based on the airborne ACTOS measurements and derived with the lidar measurements. The investigation of the optical properties shows for 14 measurement-points that the airborne-based particle light backscatter coefficient is for 1064 nm 50 % smaller than the measurements of the lidar system, 27.6 % smaller for 532 nm and 29.9 % smaller for 355 nm. These results are quite promising, since in-situ measurement based Mie-calculations of the particle light backscattering are scarce and the modelling is quite challenging. In contradiction for the particle light extinction coefficient retrieved from the airborne in situ measurements were found a good agreement. The airborne-based particle light extinction coefficient was just 7.9 % larger for 532 nm and 3.5 % smaller for 355 nm, for an assumed lidar ratio (LR) of 55 sr. The particle light extinction coefficient for 1064 nm was derived with a LR of 30 sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2 % smaller than the lidar-measurements. Also, the correlation for the particle light extinction coefficient in combination with Mie-based LR's are in agreement for typical LR's of European background aerosol.

A lot of effort has been made to understand and constrain the atmospheric aging of the organic aerosol (OA). Different parameterizations of the organic aerosol formation and evolution in the two-dimensional Volatility Basis Set (2D-VBS) framework are evaluated using ground and airborne measurements collected in the 2012 Pan-European Gas AeroSOls–climate-interaction Study (PEGASOS) field campaign in the Po Valley (Italy). A number of chemical aging schemes are examined, taking into account various functionalization and fragmentation pathways for biogenic and anthropogenic OA components. Model predictions and measurements, both at the ground and aloft, indicate a relatively oxidized OA with little average diurnal variation. Total OA concentration and O : C ratios were reproduced within experimental error by a number of chemical aging schemes. Anthropogenic SOA is predicted to contribute 15–25 % of the total OA, while SOA from intermediate volatility compounds oxidation another 20–35 %. Biogenic SOA contributions varied from 15 to 45 % depending on the modeling scheme. Primary OA contributed to around 5 % for all schemes and was comparable to the HOA concentrations of the PMF-AMS ground measurements. The average OA and O : C diurnal variation and their vertical profiles showed a surprisingly modest sensitivity to the assumed vaporization enthalpy for all aging schemes. This can be explained by the intricate interplay between the changes in partitioning of the semi-volatile compounds and their gas-phase chemical aging reactions.

The morphology and density of black carbon (BC) cores in internally mixed BC (In-BC) particles affect their mixing state and absorption enhancement. In this work, we developed a new method to measure the morphology and effective density of the BC cores of ambient In-BC particles using a single-particle soot photometer (SP2) and a volatility tandem differential mobility analyzer (VTDMA) during the CAREBeijing-2013 campaign from 8 to 27 July 2013 at Xianghe Observatory. This new measurement system can select size-resolved ambient In-BC particles and measure the mobility diameter and mass of the In-BC cores. The morphology and effective density of the ambient In-BC cores are then calculated. For the In-BC cores in the atmosphere, changes in their dynamic shape factor (χ) and effective density (ρeff) can be characterized as a function of the aging process (Dp∕Dc) measured by SP2 and VTDMA. During an intensive field study, the ambient In-BC cores had an average shape factor χ of ∼ 1.2 and an average density of ∼ 1.2 g cm−3, indicating that ambient In-BC cores have a near-spherical shape with an internal void of ∼ 30 %. From the measured morphology and density, the average shell ∕ core ratio and absorption enhancement (Eab) of ambient BC were estimated to be 2.1–2.7 and 1.6–1.9, respectively, for In-BC particles with sizes of 200–350 nm. When the In-BC cores were assumed to have a void-free BC sphere with a density of 1.8 g cm−3, the shell ∕ core ratio and Eab were overestimated by ∼ 13 and ∼ 17 %, respectively. The new approach developed in this work improves the calculations of the mixing state and optical properties of ambient In-BC particles by quantifying the changes in the morphology and density of ambient In-BC cores during aging.

Surface concentration of black carbon (BC) is a key factor for the understanding of the impact of anthropogenic pollutants on human health. The majority of Italian cities lack long-term measurements of BC concentrations since such a metric is not regulated by EU legislation. This work attempts a long-term (2001-2017) inference of equivalent black carbon (eBC) concentrations in the city of Rome (Italy) based on sun-photometry data. To this end, aerosol light absorption coefficients at the surface are inferred from the "columnar" aerosol aerosol light absorption coefficient records from the Rome Tor Vergata AERONET sun-photometer. The main focus of this work is to rescale aerosol light absorption columnar data (AERONET) to ground-level BC data. This is done by using values of mixing layer height (MLH) derived from ceilometer measurements and then by converting the absorption into eBC mass concentration through a mass-to-absorption conversion factor, the Mass Absorption Efficiency (MAE). The final aim is to obtain relevant data representative of the BC aerosol at the surface (i.e., in-situ)-so within the MLH- and then to infer a long-term record of "surface" equivalent black carbon mass concentration in Rome. To evaluate the accuracy of this procedure, we compared the AERONET-based results to in-situ measurements of aerosol light absorption coefficients (alpha(abs)) collected during some intensive field campaigns performed in Rome between 2010 and 2017. This analysis shows that different measurement methods, local emissions, and atmospheric conditions (MLH, residual layers) are some of the most important factors influencing differences between inferred and measured alpha(abs). As a general result, "inferred" and "measured" alpha(abs) resulted to reach quite a good correlation (up to r = 0.73) after a screening procedure that excludes one of the major cause of discrepancy between AERONET inferred and in-situ measured alpha(abs): the presence of highly absorbing aerosol layers at high altitude (e.g., dust), which frequently affects the Mediterranean site of Rome. Long-term trends of "inferred" alpha(abs), eBC, and of the major optical variables that control aerosol's direct radiative forcing (extinction aerosol optical depth, AOD(EXT), absorption aerosol optical depth, AOD(ABS), and single scattering albedo, SSA) have been estimated. The Mann-Kendall statistical test associated with Sen's slope was used to test the data for long-term trends. These show a negative trend for both AOD(EXT) (-0.047/decade) and AOD(ABS), (-0.007/decade). The latter converts into a negative trend for the alpha(abs) of -5.9 Mm(-1)/decade and for eBC mass concentration of -0.76 mu g/m(3)/decade. A positive trend is found for SSA (+0.014/decade), indicating that contribution of absorption to extinction is decreasing faster than that of scattering. These long-term trends are consistent with those of other air pollutant concentrations (i.e., PM2.5 and CO) in the Rome area. Despite some limitations, findings of this study fill a current lack in BC observations and may bear useful implications with regard to the improvement of our understanding of the impact of BC on air quality and climate in this Mediterranean urban region.

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

Cooking emission is one of sources for ambient volatile organic compounds (VOCs), which is deleterious to air quality, climate and human health. These emissions are especially of great interest in large cities of East and Southeast Asia. We conducted a case study in which VOC emissions from kitchen extraction stacks have been sampled in total 57 times in the Megacity Shanghai. To obtain representative data, we sampled VOC emissions from kitchens, including restaurants of seven common cuisine types, canteens, and family kitchens. VOC species profiles and their chemical reactivities have been determined. The results showed that 51.26% ± 23.87% of alkane and 24.33 ± 11.69% of oxygenated VOCs (O-VOCs) dominate the VOC cooking emissions. Yet, the VOCs with the largest ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were from the alkene and aromatic categories, accounting for 6.8–97.0% and 73.8–98.0%, respectively. Barbequing has the most potential of harming people's heath due to its significant higher emissions of acetaldehyde, hexanal, and acrolein. Methodologies for calculating VOC emission factors (EF) for restaurants that take into account VOCs emitted per person (EFperson), per kitchen stove (EFkitchen stove) and per hour (EFhour) are developed and discussed. Methodologies for deriving VOC emission inventories (S) from restaurants are further defined and discussed based on two categories: cuisine types (Stype) and restaurant scales (Sscale). The range of Stype and Sscale are 4124.33–7818.04 t/year and 1355.11–2402.21 t/year, respectively. We also found that Stype and Sscale for 100,000 people are 17.07–32.36 t/year and 5.61–9.95 t/year, respectively. Based on Environmental Kuznets Curve, the annual total amount of VOCs emissions from catering industry in different provinces in China was estimated, which was 5680.53 t/year, 6122.43 t/year, and 66,244.59 t/year for Shangdong and Guangdong provinces and whole China, respectively. Large and medium-scaled restaurants should be paid more attention with respect to regulation of VOCs.

After carbon dioxide (CO2), aerosol black carbon (BC) is considered to be the second most important contributor to global warming. This paper presents equivalent black carbon (eBC) (derived from an optical absorption method) data collected from three sites in the interior of South Africa where continuous measurements were conducted, i.e. Elandsfontein, Welgegund and Marikana, as well elemental carbon (EC) (determined by evolved carbon method) data at five sites where samples were collected once a month on a filter and analysed offline, i.e. Louis Trichardt, Skukuza, Vaal Triangle, Amersfoort and Botsalano. Analyses of eBC and EC spatial mass concentration patterns across the eight sites indicate that the mass concentrations in the South African interior are in general higher than what has been reported for the developed world and that different sources are likely to influence different sites. The mean eBC or EC mass concentrations for the background sites (Welgegund, Louis Trichardt, Skukuza, Botsalano) and sites influenced by industrial activities and/or nearby settlements (Elandsfontein, Marikana, Vaal Triangle and Amersfoort) ranged between 0.7 and 1.1, and 1.3 and 1.4 µg m−3, respectively. Similar seasonal patterns were observed at all three sites where continuous measurement data were collected (Elandsfontein, Marikana and Welgegund), with the highest eBC mass concentrations measured from June to October, indicating contributions from household combustion in the cold winter months (June–August), as well as savannah and grassland fires during the dry season (May to mid-October). Diurnal patterns of eBC at Elandsfontein, Marikana and Welgegund indicated maximum concentrations in the early mornings and late evenings, and minima during daytime. From the patterns it could be deduced that for Marikana and Welgegund, household combustion, as well as savannah and grassland fires, were the most significant sources, respectively. Possible contributing sources were explored in greater detail for Elandsfontein, with five main sources being identified as coal-fired power stations, pyrometallurgical smelters, traffic, household combustion, as well as savannah and grassland fires. Industries on the Mpumalanga Highveld are often blamed for all forms of pollution, due to the NO2 hotspot over this area that is attributed to NOx emissions from industries and vehicle emissions from the Johannesburg–Pretoria megacity. However, a comparison of source strengths indicated that household combustion as well as savannah and grassland fires were the most significant sources of eBC, particularly during winter and spring months, while coal-fired power stations, pyrometallurgical smelters and traffic contribute to eBC mass concentration levels year round., published version, peerReviewed

Black carbon (BC) aerosol particles play an important role in regulating earth's climate and their climate effects depend on their mixing state. During the CAREBeijing 2013 campaign, we measured the size-resolved mixing state of refractory BC particles in North China Plain and performed intercomparison between a single particle soot photometer (SP2) and a volatility tandem differential mobility analyzer (VTDMA). The intercomparison shows a good agreement between the optical particle diameter determined by SP2 and the mobility particle diameter determined by VTDMA for non-BC as well as for internally mixed refractory BC particles. The VTDMA shows a higher concentration of refractory particles than that of the SP2, which suggests the existence of a large fraction of low volatile non-BC aerosols. Following parameters were constrained by closure studies to improve the inversion of the mixing state of ambient BC (i.e., coating thickness (CT) and shell/core ratio (Dp / Dc)) by SP2: a) refractive indices (RI) of 1.42 and 1.67–0.56i for non-BC and rBC core components, respectively, b) refractory BC (rBC) core density of 1.2 g cm−3 for internally-mixed BC particles, and c) an effective density range of 0.25–0.45 g cm−3 for externally-mixed BC particles. Moreover, the upper limit of the measurable particle size of SP2 was extended by the leading-edge-only (LEO) fit from ~ 400 nm to ~ 550 nm as confirmed by the VTDMA measurement. Based on the improved inversion from SP2 measurement, we found that non-BC containing particles, internally-mixed BC and externally-mixed BC contribute 85–90 %, 5–7 % and 5–10 % of the total aerosol number in the size range of 200 nm to 350 nm. The number fraction of internally-mixed BC in total BC-containing aerosols (Fin) shows pronounced diurnal cycles with a peak around noon time and an apparent turnover rate up to 6–9 % h−1. Such diurnal cycles are similar to the finding of Cheng et al. (2012) suggesting the competing effect of emissions and aging processes. In this study, the observed internally-mixed BC particles in the polluted regional NCP (North China Plain) background site (Xianghe) suggest a rapid aging process of BC on the regional scale. During the intensive field study period, ~ 80 % of internally-mixed BC particles at 200–300 nm showed a Dp / Dc ratio of more than 2, accompanying with an average value of 2.3–2.8. Meanwhile, the CT of internally-mixed BC particles (200–350 nm) with rBC core size of 80–200 nm was in the range of 50–150 nm. Compared with previous measurements in developed countries, the observed BC particles on regional scale (i.e., internally-mixed BC particles) were more-aged, indicating stronger optical and climate effect of BC on the regional scale in northern China.

Heterogeneous hydrolysis of N 2 O 5 on the surface of deliquescent aerosol particles leads to HNO 3 formation and acts as a major sink of NOx in the atmosphere during nighttime. The reaction constant of this heterogeneous hydrolysis is determined by temperature (T), relative humidity (RH), aerosol particle composition as well as the surface area concentration (S). However, its parameterization in previous 3-D modelling studies did not comprehensively consider these parameters. In this investigation, we propose a sophisticated parameterization of the heterogeneous hydrolysis of N 2 O 5 with respect to T, RH, aerosol particle compositions and S, based on laboratory experiments. This new parameterization was incorporated into a 3-D fully online coupled model: COSMO-MUSCAT. As case study, we used the data from the HOPE-Melpitz campaign (10–25 September 2013). Here, we investigated the improvement of nitrate prediction over the western and central Europe. The modelled particulate nitrate mass concentrations ([NO 3 − ]) were validated by filter measurements over Germany (Neuglobsow, Schmucke, Zingst, and Melpitz). The modelled [NO 3 − ] were significantly overestimated for this period by a factor of 5–19, with the corrected NH3 emissions (reduced by 50 %) and the original parameterization of N 2 O 5 heterogeneous hydrolysis. The proposed new parameterization significantly reduces the overestimation of [NO 3 − ] by ~ 35 %. Particularly, the overestimation factor was reduced to approximately 1.4 within our case study period (September 12, 17–18 and 25, 2013), when [NO 3 − ] was dominated by local chemical formations. Furthermore, the organic coating effect on a suppression of the N 2 O 5 reaction probability may have been also significantly overestimated in previous modelling studies, due to a strong overestimation of the N 2 O 5 reaction probability on coatings. Based on the original parameterization, previous studies reported a decrease of modelled [NO 3 − ] up to 90 %, where both secondary organic aerosol (SOA) and N 2 O 5 were built-up over western and central Europe. For this case study, the suppression of organic coating was negligible over western and central Europe, with influence on [NO 3 − ] less than 2 % on average and 20 % at the most significant moment. As for a significant impact of the organic coating effect, N 2 O 5 , SOA and NH 3 need to be present when RH is high and T is low. However, those conditions were rarely fulfilled simultaneously over western and central Europe. Hence, the organic coating effect on reaction probability of N 2 O 5 over Europe may not be as important as expected in previous studies.

Aerosol-cloud interactions (ACI) constitute the single largest uncertainty in anthropogenic radiative forcing. To reduce the uncertainties and gain more confidence in the simulation of ACI, models need to be evaluated against observations, in particular against measurements of cloud condensation nuclei (CCN). Numerous observations of CCN number concentration exist, and many closure studies have been performed to predict CCN number concentrations based on particle number size distributions, chemical composition, and the κ-Köhler theory. Most of these studies provide details for short time periods or focus on special environmental conditions. These observations, however, cannot address questions of large-scale temporal and spatial CCN variability. Here we analyze long-term observations of CCN number concentrations, particle number size distributions and chemical composition from twelve sites on three continents. Eight of these stations are part of the European Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS). We group the observatories into categories according to their official classification: coastal background (Barrow, Alaska; Mace Head, Ireland; Finokalia, Crete; Noto Peninsula, Japan), rural background (Melpitz, Germany; Cabauw, the Netherlands; Vavihill, Sweden), alpine sites (Puy de Dôme, France; Jungfraujoch, Switzerland), remote forest sites (ATTO, Brazil; SMEAR, Finland) and the urban environment (Seoul, South Korea). Expectedly, CCN characteristics are highly variable across regions. However, they also vary within categories, most strongly in the coastal background group, where CCN number concentrations can vary by up to a factor of 30 within one season. In terms of particle activation behavior, most continental stations exhibit very similar relative activation ratios across the range of 0.1 to 1.0 % supersaturation. At the coastal sites the activation ratios spread more widely across the SS spectrum. Several stations show strong seasonal cycles of CCN number concentrations and particle number size distributions, e.g., at Barrow (Arctic Haze in spring), at the alpine stations (stronger influence of polluted boundary layer air masses in summer), the rain forest (wet and dry season), or Finokalia (forest fire influence in fall). The rural background and urban sites exhibit relatively little variability throughout the year while short-term variability can be high especially at the urban site. The average hygroscopicity parameter, κ, calculated from the chemical composition of submicron particles, was highest at the coastal site of Mace Head (0.6) and the lowest at the rain forest station ATTO (0.2–0.3). We performed closure studies to predict CCN number concentrations from the particle number size distribution and chemical composition measurements. The prediction accuracy for the average concentrations is high. The ratio between predicted and measured CCN concentrations is between 0.87 and 1.4. The temporal variability is also well represented, as reflected by Pearson correlation coefficients > 0.87. We also conducted a series of sensitivity studies for the ratio of predicted versus measured CCN concentration, where we varied the hygroscopicity parameter κ, and made simple assumptions for aerosol particle number concentrations and size distributions. Uncertain particle number concentrations and their size distributions significantly impair the accuracy in predicting temporal variability and hence of absolute concentrations, while the effect of uncertain κ values is limited to the predicted CCN number concentration. Information on CCN number concentrations at many locations is important to better characterize ACI and their radiative forcing. Long-term comprehensive aerosol particle characterizations are labor intensive and costly. For observatories where such efforts are out of scope to obtain nevertheless long-term information of CCN number concentrations, we recommend conducting collocated CCN number concentration and particle number size distribution measurements at individual locations throughout one year at least to derive a seasonally resolved hygroscopicity parameter. This way, CCN number concentrations can be calculated based on continued particle number size distribution information only. This approach is a good alternative to deriving kappa from time-resolved chemical composition measurements which are costly and may still not cover the appropriate size range. Additionally, given the variability in observations at sites of the same category, a certain density in spatial coverage of observations is needed, especially along coastlines. We recommend operating "migrating-CCNCs" at priority locations, identified by model evaluation, around the globe where long-term particle number size distribution data are already available.

Particle number size distributions and hygroscopic properties of marine and Saharan dust aerosol were investigated during the SAMUM-2 field study at Cape Verde in winter 2008. Aitken and accumulation mode particles were mainly assigned to the marine aerosol, whereas coarse mode particles were composed of sea-salt and a variable fraction of Saharan mineral dust. A new methodical approach was used to derive hygroscopic growth and state of mixing for a particle size range (volume equivalent) from dpve= 26 nm to 10 μm. For hygroscopic particles with dpve < 100 nm, the median hygroscopicity parameter κ is 0.35. From 100 nm < dpve < 350 nm, κ increases to 0.65. For larger particles, κ at dpve= 350 nm was used. For nearly hydrophobic particles, κ is between 0 and 0.1 for dpve < 250 nm and decreases to 0 for dpve > 250 nm. The mixing state of Saharan dust in terms of the number fraction of nearly hydrophobic particles showed the highest variation and ranges from 0.3 to almost 1. This study was used to perform a successful mass closure at ambient conditions and demonstrates the important role of hygroscopic growth of large sea-salt particles.DOI: 10.1111/j.1600-0889.2011.00569.x

An observation-based numerical study of humidity-dependent aerosol optical properties of mixed marine and Saharan mineral dust aerosol is presented. An aerosol model was developed based on measured optical and microphysical properties to describe the marine and Saharan dust aerosol at Cape Verde. A wavelength-dependent optical equivalent imaginary part of the refractive index and a scattering non-sphericity factor for Saharan dust were derived. Simulations of humidity effects on optical properties by the aerosol model were validated with relative measurements of the extinction coefficient at ambient conditions. Parametrizations were derived to describe the humidity dependence of the extinction, scattering, and absorption coefficients as well as the asymmetry parameter and single scattering albedo. For wavelengths (300–950 nm) and dry dust volume fractions (0–1), aerosol optical properties as a function of relative humidity (RH = 0–90%) can be calculated from tabulated parameters. For instance, at a wavelength of 550 nm, a volume fraction of 0.5 of dust on the total particle volume (dry conditions) and a RH of 90%, the enhancements for the scattering, extinction and absorption coefficients are 2.55, 2.46 and 1.04, respectively, while the enhancements for the asymmetry parameter and single scattering albedo are 1.11 and 1.04. DOI: 10.1111/j.1600-0889.2011.00568.x

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.

In this work, we examined the interaction of ions and neutral particles during atmospheric new particle formation (NPF) events. The analysis is based on simultaneous field measurements of atmospheric ions and total particles using a neutral cluster and air ion spectrometer (NAIS) across the diameter range 2–25 nm. The Waldstein research site is located in a spruce forest in NE Bavaria, Southern Germany, known for enhanced radon concentrations, presumably leading to elevated ionization rates. Our observations show that the occurrence of the ion nucleation mode preceded that of the total particle nucleation mode during all analyzed NPF events. The time difference between the appearance of 2 nm ions and 2 nm total particles was typically about 20 to 30 min. A cross correlation analysis showed a rapid decrease of the time difference between the ion and total modes during the growth process. Eventually, this time delay vanished when both ions and total particles did grow to larger diameters. Considering the growth rates of ions and total particles separately, total particles exhibited enhanced growth rates at diameters below 15 nm. This observation cannot be explained by condensation or coagulation, because these processes would act more efficiently on charged particles compared to neutral particles. To explain our observations, we propose a mechanism including recombination and attachment of continuously present cluster ions with the ion nucleation mode and the neutral nucleation mode, respectively.

In the fine-particle mode (aerodynamic diameter < 1 μm) non-volatile material has been associated with black carbon (BC) and low-volatile organics and, to a lesser extent, with sea salt and mineral dust. This work analyzes non-volatile particles at the tropospheric research station Melpitz (Germany), combining experimental methods such as a mobility particle-size spectrometer (3–800 nm), a thermodenuder operating at 300 °C, a multi-angle absorption photometer (MAAP), and an aerosol mass spectrometer (AMS). The data were collected during two atmospheric field experiments in May–June 2008 as well as February–March 2009. As a basic result, we detected average non-volatile particle–volume fractions of 11 ± 3% (2008) and 17 ± 8% (2009). In both periods, BC was in close linear correlation with the non-volatile fraction, but not sufficient to quantitatively explain the non-volatile particle mass concentration. Based on the assumption that BC is not altered by the heating process, the non-volatile particle mass fraction could be explained by the sum of black carbon (47% in summer, 59% in winter) and a non-volatile organic contribution estimated as part of the low-volatility oxygenated organic aerosol (LV-OOA) (53% in summer, 41% in winter); the latter was identified from AMS data by factor analysis. Our results suggest that LV-OOA was more volatile in summer (May–June 2008) than in winter (February–March 2009) which was linked to a difference in oxidation levels (lower in summer). Although carbonaceous compounds dominated the sub-μm non-volatile particle mass fraction most of the time, a cross-sensitivity to partially volatile aerosol particles of maritime origin could be seen. These marine particles could be distinguished, however from the carbonaceous particles by a characteristic particle volume–size distribution. The paper discusses the uncertainty of the volatility measurements and outlines the possible merits of volatility analysis as part of continuous atmospheric aerosol measurements., Atmospheric Chemistry and Physics, 14 (18), ISSN:1680-7375, ISSN:1680-7367

Single particle mass spectral data, collected in Paris, France, have been used to predict hygroscopic growth at the single particle level. The mass fractions of black carbon, organic aerosol, ammonium, nitrate, and sulphate present in each particle were estimated using a combination of single particle mass spectrometer and bulk aerosol chemical composition measurements. The Zdanovskii-Stokes-Robinson (ZSR) approach was then applied to predict hygroscopic growth factors based on these mass fraction estimates. Smaller particles with high black carbon mass fractions and low inorganic ion mass fractions exhibited the lowest predicted growth factors, while larger particles with high inorganic ion mass fractions exhibited the highest growth factors. Growth factors were calculated for subsaturated relative humidity (90%) to enable comparison with hygroscopic tandem differential mobility analyzer measurements. Mean predicted and measured hygroscopic growth factors for 110, 165, and 265 nm particles were found to agree within 6%. Single particle-based ZSR hygroscopicity estimates offer an advantage over bulk aerosol composition-based hygroscopicity estimates by providing additional chemical mixing state information. External mixing can be determined for particles of a given diameter through examination of the predicted hygroscopic growth factor distributions. Using this approach, 110 nm and 265 nm particles were found to be predominantly internally mixed; however, external mixing of 165 nm particles was observed periodically when thinly coated and thickly coated black carbon particles were simultaneously detected. Single particle-resolved chemical information will be useful for modeling efforts aimed at constraining cloud condensation nuclei activity and hygroscopic growth.

The influence of aerosol water uptake on the aerosol particle light scattering was examined at the regional continental research site Melpitz, Germany. The scattering enhancement factor f (RH), defined as the aerosol particle scattering coefficient at a certain relative humidity (RH) divided by its dry value, was measured using a humidified nephelometer. The chemical composition and other microphysical properties were measured in parallel. f (RH) showed a strong variation, e.g. with values between 1.2 and 3.6 at RH=85% and λ=550 nm. The chemical composition was found to be the main factor determining the magnitude of f (RH), since the magnitude of f (RH) clearly correlated with the inorganic mass fraction measured by an aerosol mass spectrometer (AMS). Hysteresis within the recorded humidograms was observed and explained by long-range transported sea salt. A closure study using Mie theory showed the consistency of the measured parameters. Keywords: aerosol particle light scattering, hygroscopic growth, scattering enhancement, aerosol mass spectrometer, field measurements, optical closure study (Published: 14 March 2014) Citation: Tellus B 2014, 66 , 22716, http://dx.doi.org/10.3402/tellusb.v66.22716

Aerosol hygroscopic growth factors and chemical properties were measured as part of the MEGAPOLI "Megacities Plume Case Study" at the urban site Laboratoire d'Hygiène de la Ville de Paris (LHVP) in the city center of Paris from June to August 2009, and from January to February 2010. Descriptive hygroscopic growth factors (DGF) were derived in the diameter range from 25 to 350 nm at relative humidities of 30, 55, 75, and 90% by applying the summation method on humidified and dry aerosol size distributions measured simultaneously with a humidified differential mobility particle sizer (HDMPS) and a twin differential mobility particle sizer (TDMPS). For 90% relative humidity, the DGF varied from 1.06 to 1.46 in summer, and from 1.06 to 1.66 in winter. Temporal variations in the observed mean DGF could be well explained with a simple growth model based on the aerosol chemical composition measured by aerosol mass spectrometry (AMS) and black carbon photometry (MAAP). In particular, good agreement was observed when sulfate was the predominant inorganic factor. A clear overestimation of the predicted growth factor was found when the nitrate mass concentration exceeded values of 10 μg m−3, e.g., during winter.

Laboratory investigations of aerosol physico-chemical properties are usually initiated by spray-drying processes. Morphology of the generated particles may vary largely under different spray-drying conditions, which may further affect the characterization of particle properties. However, only limited data is available on the morphology of nebulized submicron particles, particularly for protein particles. To fill this gap, a centrifugal particle mass analyzer coupled with a scanning mobility particle sizer was used to analyze the effective density, an indicator of particle morphology, of nebulized protein particles (bovine serum albumin and ovalbumin) in a size range from 40 to 200 nm. Results indicate that the effective density of the protein particles generated via spray-drying processes is mainly determined by the competition between the removal of liquid water and the redistribution of the solute monomers in the sprayed droplets. Factors increasing the time needed for solute monomers redistribution (e.g. lower solution concentration and larger particle dry size) or decreasing the time needed for liquid water removal (e.g. higher drying rate) may result in a lower particle effective density, meaning a semi-solid structure or partially hollow morphology. This is also confirmed by the particle hygroscopicity measured with a nano-particle hygroscopic tandem differential mobility analyzer and a high humidity tandem differential mobility analyzer. Our results suggest that the factors affecting the morphology of particles may be complex and coupled with each other, highlighting the importance of monitoring particle effective densities in studies using aerosol particles generated via spray-drying processes.

Although black carbon (BC) is one of the key atmospheric particulate components driving climate change and air quality, there is no agreement on the terminology that considers all aspects of specific properties, definitions, measurement methods, and related uncertainties. As a result, there is much ambiguity in the scientific literature of measurements and numerical models that refer to BC with different names and based on different properties of the particles, with no clear definition of the terms. The authors present here a recommended terminology to clarify the terms used for BC in atmospheric research, with the goal of establishing unambiguous links between terms, targeted material properties and associated measurement techniques.

The goals of the IGAC Aerosol Characterization Experiments (ACE) are to determine and understand the properties and controlling processes of the aerosol in a globally representative range of natural and anthropogenically perturbed environments. ACE-1 was conducted in the remote marine atmosphere south of Australia while ACE-2 was conducted in the anthropogenically modified atmosphere of the Eastern North Atlantic. In-situ shipboard measurements from the RV Discoverer (ACE-1) and the RV Professor Vodyanitskiy (ACE-2), combined with calculated back trajectories can be used to define the physical properties of the sub-micron aerosol in marine boundary layer (MBL) air masses from the remote Southern Ocean, Western Europe, the Iberian coast, the Mediterranean and the background Atlantic Ocean. The differences in these aerosol properties, combined with dimethylsulfide, sulfur dioxide and meteorological measurements provide a means to assess processes that affect the aerosol distribution. The background sub-micron aerosol measured over the Atlantic Ocean during ACE-2 was more abundant (number and volume) and appeared to be more aged than that measured over the Southern Ocean during ACE-1. Based on seawater DMS measurements and wind speed, the oceanic source of non-sea-salt sulfur and sea-salt to the background marine atmosphere during ACE-1 and ACE-2 was similar. However, the synoptic meteorological pattern was quite different during ACE-1 and ACE-2. The frequent frontal passages during ACE-1 resulted in the mixing of nucleation mode particles into the marine boundary layer from the free troposphere and relatively short aerosol residence times. In the more stable meteorological setting of ACE-2, a significant nucleation mode aerosol was observed in the MBL only for a half day period associated with a weak frontal system. As a result of the longer MBL aerosol residence times, the average background ACE-2 accumulation mode aerosol had a larger diameter and higher number concentration than during ACE-1. The sub-micron aerosol number size distributions in the air masses that passed over Western Europe, the Mediterranean, and coastal Portugal were distinctly different from each other and the background aerosol. The differences can be attributed to the age of the air mass and the degree of cloud processing. DOI: 10.1034/j.1600-0889.2000.00021.x