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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.

Sea salt aerosol (SSA) is one of the major components of primary aerosols and has significant impact on the formation of secondary inorganic aerosol particles 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 September 10–20, 2013. Meteorological conditions near the surface, wind pattern, and thermal stratification structure were well reproduced by the model. Nonetheless, coarse mode (PM1–10) particle mass concentration was substantially overestimated due to the overestimation of SSA and nitrate. Compared to filter measurements at 4 EMEP stations (coastal stations: Bilthoven, Kollumerwaard and Vredepeel; inland station: Melpitz), the modeled SSA concentrations were overestimated by a factor of 8–20. We found that the overestimation was mainly caused by the overestimated SSA emission over North Sea during September 16–20. Over the coastal regions, the SSA was injected into the continental free troposphere through an “aloft bridge” (about 500 to 1000 meter 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 broadened the influence of SSA to a larger downwind region, for example, leading to an overestimation of SSA at Melpitz, Germany by a factor of ~20. As a result, nitrate partitioning fraction (ratio between particulate nitrate and the summation of particulate nitrate and gas-phase nitric acid) increased by about 0.2 for the coarse mode nitrate due to the overestimation of SSA at Melpitz, but no significant difference in the partitioning fraction for the fine mode nitrate. About 140 % overestimation of the coarse mode nitrate was resulted from the influence of SSA at Melpitz. On the other hand, the overestimation of SSA inhibited the nitrate formation in the fine mode by about 20 %, because of the increased consumption of precursors by coarse mode nitrate formation.

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

Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates accuracy, particle sizing, and unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10–20 % for particles in the range of 0.9 up to 3 μm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 μm in aerodynamic diameter should be only used with caution. For particles larger than 3 μm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. This uncertainty of the particle number size distribution has especially to be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5–3 μm is needed.

The German Ultrafine Aerosol Network (GUAN) is a cooperative atmospheric observation network, which aims at improving the scientific understanding of aerosol-related effects in the troposphere. The network addresses research questions dedicated to both climate- and health-related effects. GUAN's core activity has been the continuous collection of tropospheric particle number size distributions and black carbon mass concentrations at 17 observation sites in Germany. These sites cover various environmental settings including urban traffic, urban background, rural background, and Alpine mountains. In association with partner projects, GUAN has implemented a high degree of harmonisation of instrumentation, operating procedures, and data evaluation procedures. The quality of the measurement data is assured by laboratory intercomparisons as well as on-site comparisons with reference instruments. This paper describes the measurement sites, instrumentation, quality assurance, and data evaluation procedures in the network as well as the EBAS repository, where the data sets can be obtained (doi:10.5072/guan).

Simultaneous measurements of aerosol size, distribution of number, mass, and chemical compositions were conducted in the winter of 2007 in Beijing using a Twin Differential Mobility Particle Sizer and a Micro Orifice Uniform Deposit Impactor. Both material density and effective density of ambient particles were estimated to be 1.61 ± 0.13 g cm(-3) and 1.62 ± 0.38 g cm(-3) for PM(1.8) and 1.73 ± 0.14 g cm(-3) and 1.67 ± 0.37 g cm(-3) for PM(10). Effective density decreased in the nighttime, indicating the primary particles emission from coal burning influenced the density of ambient particles. Size-resolved material density and effective density showed that both values increased with diameter from about 1.5 g cm(-3) at the size of 0.1 μm to above 2.0 g cm(-3) in the coarse mode. Material density was significantly higher for particles between 0.56 and 1.8 μm during clean episodes. Dynamic Shape Factors varied within the range of 0.95-1.13 and decreased with particle size, indicating that coagulation and atmospheric aging processes may change the shape of particles.

Residential wood burning is becoming an increasingly important cause of air quality problems since it has become a popular source of alternative energy to fossil fuel. In order to characterize the contribution of residential wood burning to local particle pollution, a field campaign was organized at the village of Seiffen (Saxony, Germany). During this campaign, an Aerosol Mass Spectrometer (AMS) was deployed in parallel to a PM1 high volume filter sampler. The AMS mass spectra were analyzed using Positive Matrix Factorization (PMF) to obtain detailed information about the organic aerosol (OA). Biomass-burning organic aerosol (BBOA), Hydrocarbon-like organic aerosol (HOA), and Oxygenated Organic Aerosol (OOA) were identified and represented 20%, 17% and 62% of total OA, respectively. Additionally, Polycyclic Aromatic Hydrocarbons (PAH) were measured by the AMS with an average concentration of 10 ng m−3 and short term events of extremely high PAH concentration (up to 500 ng m−3) compared to the mean PAH value were observed during the whole measurement period. A comparison with the results from PM1 filter samples showed that the BBOA factor and the AMS PAH are good indicators of the total concentration of the different monosaccharide anhydrides and PAH measured on the filter samples. Based on its low correlation with CO and the low car traffic, the HOA factor was considered to be related to residential heating using liquid fuel. An influence of the time of the week (week vs. weekend) on the diurnal profiles of the different OA components was observed. The weekdays were characterized by two maxima; a first one early in the morning and a stronger one in the evening. During the weekend days, the different OA components principally reached only one maximum in the afternoon. Finally, the PAH emitted directly from residential wood combustion was estimated to represent 1.5% of the total mass of the BBOA factor and around 62% of the total PAH concentration measured at Seiffen. This result highlights the important contribution of residential wood combustion to air quality and PAH emissions at the sampling place, which might have a significant impact on human health. Moreover, it also emphasizes the need for a better time resolution of the chemical characterization of toxic particulate compounds in order to provide more information on variations of the different sources through the days as well as to better estimate the real human exposure.

Ammonium nitrate and several organic compounds such as dicarboxylic acids (e.g. succinic acid, glutaric acid), some Polycyclic Aromatic Hydrocarbon (PAHs) or some n-alkanes are semi-volatile. The transition of these compounds between the gas and particulate phase may significantly change the aerosol particles radiative properties, the heterogeneous chemical properties, and, naturally, the total particulate mass concentration. To better assess these time-dependent effects, three intensive field experiments were conducted in 2008–2009 at the Central European EMEP research station Melpitz (Germany) using an Aerodyne Aerosol Mass Spectrometer (AMS). Data from all seasons highlight organic matter as being the most important particulate fraction of PM1 in summer (59%) while in winter, the nitrate fraction was more prevalent (34.4%). The diurnal variation of nitrate always showed the lowest concentration during the day while its concentration increased during the night. This night increase of nitrate concentration was higher in winter (ΔNO3− = 3.6 μg m−3) than in summer (ΔNO3− = 0.7 μg m−3). The variation in particulate nitrate was inherently linked to the gas-to-particle-phase equilibrium of ammonium nitrate and the dynamics of the atmosphere during day. The results of this study suggest that during summer nights, the condensation of HNO3 and NH3 on pre-existing particles represents the most prevalent source of nitrate, whereas during winter, nighttime chemistry is the predominant source of nitrate. During the summer 2008's campaign, a clear diurnal evolution in the oxidation state of the organic matter became evident (Organic Mass to Organic Carbon ratio (OM/OC) ranging from 1.65 during night to 1.80 during day and carbon oxidation state (OSc) from −0.66 to −0.4), which could be correlated to hydroxyl radical (OH) and ozone concentrations, indicating a photochemical transformation process. In summer, the organic particulate matter seemed to be heavily influenced by regional secondary formation and transformation processes, facilitated by photochemical production processes as well as a diurnal cycling of the substances between the gas and particulate phase. In winter, these processes were obviously less pronounced (OM/OC ranging from 1.60 to 1.67 and OSc from −0.8 to −0.7), so that organic matter apparently originated mainly from aged particles and long range transport.

This study discusses the evolution of particle number size distribution during episodes of heavy pollution and new particle formation in the urban atmosphere of Beijing to quantify the effects of dynamic processes (coagulation and condensation) on the particle number size distribution. During a heavy-pollution event, an extremely low number concentration of 3–10 nm particles (on average 46 cm−3) was observed. This is because nucleation-mode particles were easily removed by strong coagulational scavenging of larger particles under this condition. In addition, a large condensation sink (on average 0.13 s−1) restrained nucleation, which is one of the major sources of nucleation-mode particles. Conversely, during a new-particle formation event, the small condensation sink (0.01 s−1) of precursor facilitated nucleation. At the same time, preexisting particles had little ability to scavenge newly formed particles (around 1 nm) and allowed them to grow to a detectable size (larger than 3 nm currently). We suggest that the effects of dynamic processes (coagulation and condensation) on particle size distribution should be stressed under some extreme conditions of the relatively polluted urban atmosphere in addition to traffic and meteorological factors.

Observations of the tropical atmosphere are fundamental to the understanding of global changes in air quality, atmospheric oxidation capacity and climate, yet the tropics are under-populated with long-term measurements. The first three years (October 2006–September 2009) of meteorological, trace gas and particulate data from the global WMO/Global Atmospheric Watch (GAW) Cape Verde Atmospheric Observatory Humberto Duarte Fonseca (CVAO; 16° 51′ N, 24° 52′ W) are presented, along with a characterisation of the origin and pathways of air masses arriving at the station using the NAME dispersion model and simulations of dust deposition using the COSMO-MUSCAT dust model. The observations show a strong influence from Saharan dust in winter with a maximum in super-micron aerosol and particulate iron and aluminium. The dust model results match the magnitude and daily variations of dust events, but in the region of the CVAO underestimate the measured aerosol optical thickness (AOT) because of contributions from other aerosol. The NAME model also captured the dust events, giving confidence in its ability to correctly identify air mass origins and pathways in this region. Dissolution experiments on collected dust samples showed a strong correlation between soluble Fe and Al and measured solubilities were lower at high atmospheric dust concentrations. Fine mode aerosol at the CVAO contains a significant fraction of non-sea salt components including dicarboxylic acids, methanesulfonic acid and aliphatic amines, all believed to be of oceanic origin. A marine influence is also apparent in the year-round presence of iodine and bromine monoxide (IO and BrO), with IO suggested to be confined mainly to the surface few hundred metres but BrO well mixed in the boundary layer. Enhanced CO2 and CH4 and depleted oxygen concentrations are markers for air-sea exchange over the nearby northwest African coastal upwelling area. Long-range transport results in generally higher levels of O3 and anthropogenic non-methane hydrocarbons (NMHC) in air originating from North America. Ozone/CO ratios were highest (up to 0.42) in relatively fresh European air masses. In air heavily influenced by Saharan dust the O3/CO ratio was as low as 0.13, possibly indicating O3 uptake to dust. Nitrogen oxides (NOx and NOy) show generally higher concentrations in winter when air mass origins are predominantly from Africa. High photochemical activity at the site is shown by maximum spring/summer concentrations of OH and HO2 of 9 × 106 molecule cm−3 and 6 × 108 molecule cm−3, respectively. After the primary photolysis source, the most important controls on the HOx budget in this region are IO and BrO chemistry, the abundance of HCHO, and uptake of HOx to aerosol.

The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 μm that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate.

The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influences on the frequency of new particle formation events at this area. The factors affecting the coagulation sink are evaluated. The relatively lower ambient relative humidities may weaken the coagulation sink and facilitate the occurrence of new particle formation events during noontime, while the surmise of nucleation and growth involving organic matter may imply an actually higher coagulation sink than expected. These factors have a significant influence on the ultimate fate of the newly formed nuclei and new particle formation. A comparison of event and non-event days indicates that the coagulation sink is not the only decisive factor affecting new particle formation, other factors including the precursor vapors and photochemical activity are none the less important either. Competition of coagulation sink and high source rate leads to the occurrence of new particle formation events at Xinken.

An aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) combined with a thermodenuder (TD) was used to investigate laboratory-generated aerosol particles with regard to their volatility and chemical content. The performance of the setup was tested first by using ammonium sulfate particles. Organic compounds have been measured including humic acid, fulvic acid, succinic acid and its disodium salt, 2-methylsuccinic acid, fumaric acid, α-ketoglutaric acid, and glutaric acid. Among them, humic acid, fulvic acid, and disodium succinate show a non-volatile fraction at 300 °C, while the other organic compounds are more volatile. Comparisons of mass spectra at different temperatures showed that significant differences in mass spectra of humic and fulvic acids are observed, indicating that their molecules changed during or after volatilization. At lower temperatures, the changes in humic acid are more likely due to the evaporation of small organic molecules or decomposition of aliphatic groups. The mass losses of the CO 2 + fragment for both humic and fulvic acids at higher temperatures may arise from decarboxylation processes. The different mass spectra for humic and fulvic acids before and after TD also suggest that one should be careful in interpretation of volatility measurements because some molecule structures may change after being heated, especially for the non-volatile multifunctional compounds.

Two-year measurements of particle number size distribution (3 nm–10 μm) were conducted in Beijing, China since March 2004. Their seasonal, weekly and diurnal variations and dependencies on meteorological parameters were investigated. The annual average particle number concentrations of the nucleation mode (3–20 nm), Aitken mode (20–100 nm), and accumulation mode (0.1–1 μm) are 9000 cm−3, 15,900 cm−3, and 7800 cm−3, respectively. Particle number concentrations in Beijing are generally higher than that in cities of developed countries, especially for the accumulation mode particles. Both the highest total particle number concentration and the lowest volume concentration occurred in spring due to the frequent nucleation events. However, the minimum particle number concentration was observed in summer, and the maximum volume concentration in fall. The diurnal variation of the nucleation mode particles was mainly influenced by nucleation events, primarily in spring and winter. The diurnal variation of number concentration of the Aitken mode particles closely correlates with the traffic densities in all the four seasons. At the same time, obvious contribution of the growth of the nucleation mode to the number concentration of the Aitken mode particle has been also found in spring, summer, and fall. Significant differences in diurnal patterns of particle number concentrations between workdays and weekends are not observed in Beijing. Local wind speed plays an important role in shaping the particle number size distributions in the urban area of Beijing. With increasing wind speed, the nucleation and coarse mode particle number concentrations increase, while the number concentrations of the Aitken mode and accumulation mode particles decrease. A “U-shape relationship” between the total particle volume concentration and wind speed is observed. Frequently low wind speed (lower than 3 m s−1) in Beijing is one of key factors leading to the poor air quality and low visibility.

A Volatility-Tandem-Differential-Mobility-Analyzer (VTDMA) and a Differential Mobility Particle Sizer (DMPS) were used to determine the number and mass concentration of externally mixed aerosol particles in urban background air. In the VTDMA the less-volatile (LV) particle fraction was measured at 300°C for particles in the size range 20–250 nm. The LV particle fraction was converted to the number concentration of LV particles (NLV) and the mass concentration (MLV). MLV was compared with the mass concentration of black carbon (MBC) measured by a Multi-Angle Absorption Photometer (MAAP). The DMPS and VTDMA data were used for calculating scattering and absorption coefficients (σSP and σ AP) with a Mie model and compared with σ SP and σ AP measured with a TSI nephelometer and the MAAP. The model was run by assuming external and internal mixing of absorbing and scattering aerosol. The best fit of measured and modeled σ SP and σ AP was sought by varying the refractive index. During periods dominated by local e...

Continuous measurements of aerosol number size distribution in the range of 3 nm–10 μm were performed in Pearl River Delta (PRD), China. These measurements were made during the period of 3 October to 5 November in 2004 at rural/coastal site, Xinken (22°37′N, 113°35′E, 6 m above sea level), in the south suburb of Guangzhou City (22°37′N, 113°35′E, 6 m above sea level), using a Twin Differential Mobility Particle Sizer (TDMPS) combined with an Aerodynamic Particle Sizer (APS). The aerosol particles at Xinken were divided into four groups according to the observation results: nucleation mode particles (3–30 nm), Aitken mode particles (30–130 nm), accumulation mode particles (130–1000 nm) and coarse mode particles (1–10 μm). Concentrations of nucleation mode, Aitken mode and accumulation mode particles were observed in the same order of magnitude (about 10,000 cm−3), among which the concentration of Aitken mode particle was the highest. The Aitken mode particles usually had two peaks: the morning peak may be caused by the land–sea circulation, which is proven to be important for transporting aged aerosols back to the sampling site, while the noon peak was ascribed to the condensational growth of new particles. New particle formation events were found on 7 days of 27 days, the new particle growth rates ranged from 2.2 to 19.8 nm h−1 and the formation rates ranged from 0.5 to 5.2 cm−3 s−1, both of them were in the range of typical observed formation rates (0.01–10 cm−3 s−1) and typical particle growth rates (1–20 nm h−1). The sustained growth of the new particles for several hours under steady northeast wind indicated that the new particle formation events may occur in a large homogeneous air mass.

Though the importance of HONO as an OH precursor has been recognized for years, its chemical formation pathway is still not well understood. This inhibited the simulations of HONO and observation-based formation rates provided an alternative for the air quality models. However, HONO formation rate derived from certain period may be significantly influenced by uncertainties in transport and emission processes. In this study the use of large sample and scaling methods were recommended in the calculation of HONO formation rate. During the Program of Regional Integrated Experiments of Air Quality over Pear River Delta (PRIDE-PRD2004), good correlations between HONO and NO 2 were found supporting the involvement of NO 2 in HONO formation. An average NO 2 -to-HONO nighttime conversion rate C HONO of 1.6 % h - 1 was derived at a non-urban site Xinken. This conversion rate was comparable to other field measurements and could not be explained by gas phase reactions only. If assumed that HONO was formed only on the ground surface, the observed conversion rate could be explained by the reactions of NO 2 on ground surfaces only if three deposited NO 2 lead to one HONO released. The emission factor of HONO and its sampling interferences during the measurements were also evaluated in this article.

The aims of the Program of Regional Integrated Experiments on Air Quality over Pearl River Delta of China 2004 (PRIDE-PRD2004) were to characterize in depth the pollution, and to improve the understanding of the chemical and radiative processes in the atmosphere of Pearl River Delta (PRD) in South-Eastern China. This comprehensive program integrated ground-base in situ measurements, vertical observations (including aircraft) and model simulations. The intensive field campaign was conducted from 4 October to 5 November 2004 at two super-sites: an urban site in Guangzhou city (23.13°N, 113.26°E) and a non-urban site at Xinken (22.61°N, 113.59°E). They were coordinated with concurrent meteorological observations as well as measurements at stations of a regional monitoring network. Quality control and quality assurances, application of closure studies and observation-based modeling were the key elements of the research strategies for the PRIDE-PRD2004 campaign. Knowledge and understanding of the important issues, including 3-D distribution of air pollution, ozone formation process and its control strategies, sources of volatile organic compounds, chemical and physical characteristics and radiative properties of aerosols, and the important role of nitrous acid atmospheric chemistry, have been improved substantially by this study.

A better characterisation of the optical properties of biomass burning aerosol as a function of the burning conditions is required in order to quantify their effects on climate and atmospheric chemistry. Controlled laboratory combustion experiments with different fuel types were carried out at the combustion facility of the Max Planck Institute for Chemistry (Mainz, Germany) as part of the "Impact of Vegetation Fires on the Composition and Circulation of the Atmosphere" (EFEU) project. The combustion conditions were monitored with concomitant CO2 and CO measurements. The mass scattering efficiencies of 8.9±0.2 m2 g−1 and 9.3±0.3 m2 g−1 obtained for aerosol particles from the combustion of savanna grass and an African hardwood (musasa), respectively, are larger than typically reported mainly due to differences in particle size distribution. The photoacoustically measured mass absorption efficiencies of 0.51±0.02 m2 g−1 and 0.50±0.02 m2 g−1 were at the lower end of the literature values. Using the measured size distributions as well as the mass scattering and absorption efficiencies, Mie calculations provided effective refractive indices of 1.60−0.010i (savanna grass) and 1.56−0.010i (musasa) (λ=0.55 μm). The apparent discrepancy between the low imaginary part of the refractive index and the high apparent elemental carbon (ECa) fractions (8 to 15%) obtained from the thermographic analysis of impactor samples can be explained by a positive bias in the elemental carbon data due to the presence of high molecular weight organic substances. Potential artefacts in optical properties due to instrument bias, non-natural burning conditions and unrealistic dilution history of the laboratory smoke cannot be ruled out and are also discussed in this study.

A new method based on the combination of a differential mobility analyser (DMA) and aerodynamic particle sizer (APS) is presented, to measure the aerodynamic hygroscopic growth factor of aerosol particles around one micrometer in size. The DMA is used as a filter, selecting a size fraction of the ambient aerosol. One half of the selected monodisperse aerosol is sized in dry state in a first APS, while the second half of the aerosol is humidified, and then sized in a second APS. By comparing the particle size distributions measured in the first and second APS, the hygroscopic growth factor can be derived as a function of relative humidity (RH). Hygroscopic growth factors can be measured at RHs up to 90%. Particle modes of different hygroscopicity can be distinguished, giving information on the mixing state and the fraction of more and less hygroscopic particles. The system was tested and characterised in the laboratory, using inorganic salt particles ( ( NH 4 ) 2 SO 4 ) of known hygroscopic growth behaviour. It agreed with growth curves given in the literature, within the measurement uncertainty.

An airfreight container with automated instruments for measurement of atmospheric gases and trace compounds was operated on a monthly basis onboard a Boeing 767-300 ER of LTU International Airways during long-distance flights from 1997 to 2002 (CARIBIC, Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, http://www.caribic-atmospheric.com). Subsequently a more advanced system has been developed, using a larger capacity container with additional equipment and an improved inlet system. CARIBIC phase #2 was implemented on a new long-range aircraft type Airbus A340-600 of the Lufthansa German Airlines (Star Alliance) in December 2004, creating a powerful flying observatory. The instrument package comprises detectors for the measurement of O3, total and gaseous H2O, NO and NOy, CO, CO2, O2, Hg, and number concentrations of sub-micrometer particles (>4 nm, >12 nm, and >18 nm diameter). Furthermore, an optical particle counter (OPC) and a proton transfer mass spectrometer (PTR-MS) are incorporated. Aerosol samples are collected for analysis of elemental composition and particle morphology after flight. Air samples are taken in glass containers for laboratory analyses of hydrocarbons, halocarbons and greenhouse gases (including isotopic composition of CO2) in several laboratories. Absorption tubes collect oxygenated volatile organic compounds. Three differential optical absorption spectrometers (DOAS) with their telescopes mounted in the inlet system measure atmospheric trace gases such as BrO, HONO, and NO2. A video camera mounted in the inlet provides information about clouds along the flight track. The flying observatory, its equipment and examples of measurement results are reported.

An aerosol inlet pipe with an internal diameter of 2.8 cm and overall length of 300 m was designed for deployment on a tall meteorological tower. During this work the transport losses of aerosol particles across the pipe were experimentally ascertained for particle diameters between 10 and 400 nm, and sampling flows between 20 and 60 l min−1. The transport losses were determined by simultaneously measuring particle number size distributions of ambient aerosol upstream and downstream of the 300 m pipe using two scanning mobility particle sizers (SMPS). At a sampling flow of 40 l min−1, the particle penetration attained a maximum of 0.97 (±0.01) for particles in the size range between 50 and 200 nm. This particle penetration decreased to 0.66 (± 0.03) for 20 nm particles, and 0.29 (±0.04) for 10 nm particles. Theoretical values for the particle penetration through the pipe were calculated based on expressions accounting for Brownian diffusion in laminar, or fully turbulent flow. In addition, computational f...

New particle formation is one of the major sources of atmospheric aerosol particles. Beside daytime nucleation, nocturnal new particle formation was also found in different regions around the world. Compared with daytime nucleation events, the understanding of nocturnal ones is still sparse. The variety of aerosol particle physico-chemical properties, including particle number size distribution, volatility and hygroscopicity were measured in the North China Plain during July–August 2013. During the observation period, rapid increase in ultrafine particle number concentration was attributed to new particle formation. The nocturnal new particle formation rate was 45 cm–3s–1, which is 1.25 times higher than an observed daytime value. Condensation sink was found to be 0.055 s–1.

Background The link between particulate air pollution and cardiovascular (CVD) mortality has been investigated. However, there is little direct evidence that reduction measures which decrease particulate air pollution would lead to a reduction in CVD mortality. Objectives In Beijing, China, air quality improvement strategies were developed and actions were taken before and during the 2008 Olympic and Paralympic Games. Taking advantage of this opportunity, the aim of the study was to assess the effects of changes in particulate air pollution before (May 20–July 20, 2008), during (August 1–September 20, 2008) and after (October 1–December 1, 2008) the Olympics period. Methods Concentrations of air pollution, meteorology and CVD death counts were obtained from official networks and monitoring sites located on the Peking University campus. Air pollution effects with lags of 0–4 days as well as of the 5-day average on cause-specific CVD mortality were investigated for the complete study period (May 20–December 1, 2008) using Quasi-Poisson regression models. Different gender and age subgroups were taken into account. Additionally, effect modification by air mass origin was investigated. In a second step, air pollution effects were estimated for the three specific periods by including an interaction term in the models. Results We observed large concentration decreases in all measured air pollutants during the unique pollution intervention for the Beijing 2008 Olympics. For the whole period, adverse effects of particulate air pollution were observed on CVD mortality with a 1-day delay as well as for the 5-day average exposure, e.g. an 8.8% (95%CI: 2.7–15.2%) increase in CVD mortality with an interquartile range increase in ultrafine particles. The effects were more pronounced in females, the elderly and for cerebrovascular deaths, but not modified by air mass origin. The specific sub-period analysis results suggested that the risks of CVD mortality were lowest during the Olympic Games where strongest reduction measures have been applied. Conclusions The results indicated that the reduction of air pollution due to air quality control measures led to a decreased risk of CVD mortality in Beijing. Our findings provide new insight into efforts to reduce ambient air pollution.

We report emissions of mass, light absorption, particle number, chemical composition and size-resolved organic species from an industrial boiler that burned natural gas and residual oil. Organic compounds detected from oil combustion are mainly alkanes; it is not a major source of identifiable polyaromatic hydrocarbons. Elemental carbon (EC) and organic carbon (OC) make up approximately 38% and 15% of the particles from oil burning, respectively. Mass emissions from natural gas were below detection limits. A number peak of ultrafine aerosol (diameters lower than 10 nm) was always associated with oil burning. Burning at full power produced the greatest number of particles in the accumulation mode. Natural gas also produced fine particles, but at a much lower rate. The emission rate of light-absorbing particles from this relatively new boiler is lower than that in current emission inventories. However, real-time measurements show a large contribution to emitted light absorption from boiler warm-up and transients, even those with very short durations. The measured absorption is best explained with a constant absorption cross-section for EC, rather than predictions based on size distribution or mixed aerosol; this finding is consistent with EC in fractal-aggregate form. We compare the emissions with those of a lignite stoker, which this boiler replaced during environmental cleanup in the mid-1990s. Emissions of mass, light absorption and particles are lowest from natural gas, but the oil boiler is also a substantial improvement: emissions of particulate matter are 100 times lower, and emitted absorption is three times lower. However, the oil-burning emissions have a greater net warming effect per mass than those of the lignite plant.

In developing countries, aerosol particles damage the health of hundreds of millions of people. Migration from the country side to megacities increases emissions and exposure to particles. Some countries have started to limit emissions based on particulate mass, but this may increase particle number concentrations. In this study we discuss some earlier measurements carried out in the developing world and compare results from one-week measurement campaigns concerning the particle number size distribution and PM10 mass concentrations in New Delhi, India and Beijing, China. Our results show that submicron particle concentrations are high in both places. The average PM10 concentration was 360 μg/m3 in New Delhi and 120 μg/m3 in Beijing. The corresponding total particle number concentrations in the size range 3–800 nm were 63 000 cm−3 and 35 000 cm−3. Number and mass concentrations and their characteristics showed significantly different behaviour between these two locations, which stresses the importance of long-term simultaneous measurements of both quantities in different types of megacities.

Ambient aerosol has been identified as a major pollutant affecting human health. Standards to reduce particles mass concentrations have therefore been established in many countries. Recent studies suggest that the number concentration of aerosol particles, which is dominated by the ultrafine size range smaller than 100 nm in diameter, may be independently associated with health effects. Currently, epidemiological evidence for such effects is conflicting. We have measured aerosol size distributions at two stations (urban background, street canyon) located at a distance of 1.5 km for a time period of 1 year. Number concentrations and particle size distributions at both sites were significantly different. Short-term correlation between the two sites was weak for individual measurements of number concentrations and size bins of ultrafine particles (0.19-0.46). Correlation coefficients for hourly and daily averages in selected size ranges ranged from 0.35 to 0.46. On the other hand, the correlation coefficient for daily average particle volume concentrations was found to be 0.67. About 10% to 20% of the population of European cities lives close to roads with traffic densities comparable to our site. The underestimation of the exposure of a considerable part of a study population may therefore severely influence the outcome of epidemiological studies focused on health effects associated with ultrafine particles. A single background measurement site may not be sufficient for exposure assessment in these studies without taking spatial and temporal variability into account.

Within the ground-based cloud passage experiment FEBUKO, which was carried out at the mountain ridge Thuringer Wald (Germany) during October 2001 and 2002, the dry number size distribution and hygroscopic growth of aerosol particles upwind cloud and the dry number size distributions of interstitial particles and cloud droplet residuals inside cloud were measured at connected flow conditions. The connected flow between the upwind and in-cloud summit site was meteorologically predicted and experimentally confirmed for three selected cloud events. For these events, it could be verified that entrainment and droplet deposition had only a minor influence on the evolution of the particle size distribution between the two sites. Hence, the size resolved soluble volume fraction of the cloud input aerosol particles determined from the hygroscopic growth measurements could be related to the particle activation inferred from the particle size distributions observed inside cloud. The shape and steepness of the scavenging fraction as a function of particle diameter was found to correlate with the increase of soluble volume fraction with size, which had implications for the droplet activation diameter of the cloud condensation nuclei (CCN) that ranged between 110 and 180 nm. The minimum soluble volume fraction e min that was required to serve as CCN was determined for three different dry diameters from the relation of the particle volume fraction and scavenging fraction. From the comparison with e min predictions from classical Kohler theory it is inferred that aerosol particles remained in the interstitial phase although they should have been activated. A discussion of different processes which have the general ability to explain this finding favoured the hypothesis of organic surface films retarding the uptake of water molecules.

The concentration and size distribution of atmospheric particles were traced upwind, inside and downwind a hill cap cloud within the ground-based cloud passage experiment FEBUKO, which was carried out at the mountain ridge Thuringer Wald (Germany) during October 2001 and 2002. Three cloud events were examined in detail for which the connected flow between all three sites was meteorologically confirmed and the influence of entrainment and local sources on particle concentration and size distribution was only of minor importance. Modifications of the number size distributions between 60 and 300 nm particle diameter that are attributed to cloud processing were observed comparing upwind and downwind dry particle size distributions. Despite a small interference of droplet deposition, a maximum in-cloud mass production of 0.38 μg m−3 was found accounting for 5% of the upwind aerosol mass. The corresponding mass production rate was estimated to 1.16 μg m−3 h−1. A formation of new ultra-fine particles was detected in the outflow of the orographic clouds during nighttime yielding number concentrations up to 300 cm−3 at a pre-existing dry particle surface area of about 300 μm2 cm−3. At a more than twice as high particle surface area, i.e. when adsorption of condensable gases on existing particles became more important, no new particle formation was observed. Whereas the in-cloud mass production proceeded rather continuously throughout the cloud events, the particle production occurred during periods of 15 min up to 2 h within the cloud events. In the absence of actinic radiation, ternary nucleation of gaseous substances outgassing from the evaporating droplets at high relative humidity is hypothesized as the most likely particle formation mechanism but the reason for the temporary appearance of the particle production is not known.

This contribution presents characterisation efforts of the gas phase and particle phase main components during the FEBUKOorographic cloud passage experiments in autumn 2001 and 2002 in the Thuringer Wald (Germany). Three events out of a total of 14 were chosen as the best events considering all meteorological conditions. Gas phase and size- segregated particle phase data obtained from physical (dry size distribution) and chemical (particle mass, main ions, OCEC, and water-soluble metals) measurements are presented for the upwind site. The total particulate mass concentration (PM10) was found to be between 8 and 17m gm � 3 . Particles with an aerodynamic diameter up to 1.2mm contribute about 80% of the mass concentration. About 90% of the total ion concentration consists of nitrate, sulphate and ammonium. The OC concentration in all three events amounts to about 1.0m gm � 3 , whereas EC concentrations were between 0.40 and 1.0m gm � 3 . The contribution of OC and EC to stage mass ranged from 5% to 35% and from 2% to 17%, respectively. The water content of particles was estimated to be 16-18%. Physical and chemical mass closure is discussed in detail and the results are in a reasonable agreement. The complex data set obtained for each event can be used in the initialisation of models for the multiphase processes during and after the cloud passage of the characterised air mass. r 2005 Elsevier Ltd. All rights reserved.

Emissions from vehicular traffic are considered to be a major source of anthropogenic submicrometer particles in the urban environment. In this study, volatile and non-volatile number and volume fractions were distinguished in particles sampled for three consecutive days (Friday, Saturday, and Sunday) close to a highway (HW) (A4) in Germany and for one day in the urban area of Aachen, Germany. A volatility tandem differential mobility analyzer (VTDMA) and a thermodenuder (TD) combined with two scanning mobility particle sizers (SMPS) were used to get insight into a size-resolved mixing state of volatile and non-volatile particle fractions. Operating the VTDMA at 280 °C, the number size distribution of non-volatile particle cores was determined for initial particle sizes of 30, 50, 80, and 150 nm. The number size distributions from 10 to 400 nm of ambient and non-volatile aerosol particles were measured by using parallel a SMPS and TD/SMPS combination, respectively. Number size distributions measured near the HW showed a bimodal size distribution with a maximum number concentration at particle sizes between 10 and 20 nm. The TD/SMPS results for the HW site revealed that the nucleation mode disappeared after heating (completely volatile) and in total 10–20% by number of traffic-related particles were non-volatile. The VTDMA results revealed that only 22% of the 30 nm particles had a non-volatile core above the instrument detection limit of 10 nm. With increasing particle diameter, this non-volatile number fraction increased to ca. 60% for 50 nm particles and to approximately 100% for 80 and 150 nm particles. These findings mean that each particle in the upper Aitken and lower accumulation mode range contains a non-volatile core. With increasing traffic influence the number fraction of less-volatile particles representing mainly primary soot emissions increases to 62% for 50 nm particles and 71% for 80 nm particles.

Beddows, D. C. S. ... et. al.-- 22 pages, 11 figures, 1 table, supplementary material related to this article is available online at http://www.atmos-chem-phys.net/14/4327/2014/acp-14-4327-2014-supplement.pdf, Clusteranalysis of particle number size distributions frombackground sites across Europeis presented. This generated a total of nine clusters of particle size distributions which could be further combined into two main groups, namely: a south-to-north category (four clusters) and a west-to-east category (five clusters). The first group was identified as most frequently being detected inside and around northern Germany and neighbouring countries, showing clear evidence of local afternoon nucleation and growth events that could be linked to movement of air masses from south to north arriving ultimately at the Arctic contributing to Arctic haze.The second group of particle size spectra proved to have narrower size distributions and collectively showed a dependence of modal diameter upon the longitude of the site (west to east) at which they were most frequently detected.These clusters indicated regional nucleation (at the coastal sites) growing to larger modes further inland. The apparent growth rate of the modal diameter was around 0.6-0.9 nm h-1. Four specific air mass back-trajectories were successively taken as case studies to examine in real time the evolution of aerosol size distributions across Europe. While aerosol growth processes can be observed as aerosol traverses Europe, the processes are often obscured by the addition of aerosol by emissions en route. This study revealed that some of the 24 stations exhibit more complex behaviour than others, especially when impacted by local sources or a variety of different air masses. Overall, the aerosol size distribution clustering analysis greatly simplifies the complex data set and allows a description of aerosol aging processes, which reflects the longer-term average development of particle number size distributions as air masses advect across Europe. © 2014 Author(s), The National Centre for Atmospheric Science is funded by the UK Natural Environment Research Council. This work was also supported by the European Union EUCAARI (Contract Ref. 036833) and EUSAAR (Contract Ref. 026140) research projects

A newly developed framework for quantifying aerosol particle diversity and mixing state based on information-theoretic entropy is applied for the first time to single particle mass spectrometry field data. Single particle mass fraction estimates for black carbon, organic aerosol, ammonium, nitrate and sulfate, derived using single particle mass spectrometer, aerosol mass spectrometer and multi-angle absorption photometer measurements are used to calculate single particle species diversity (Di). The average single particle species diversity (Dα) is then related to the species diversity of the bulk population (Dγ) to derive a mixing state index value (χ) at hourly resolution. The mixing state index is a single parameter representation of how internally/externally mixed a particle population is at a given time. The index describes a continuum, with values of 0 and 100% representing fully external and internal mixing, respectively. This framework was applied to data collected as part of the MEGAPOLI winter campaign in Paris, France, 2010. Di values are low (~ 2) for fresh traffic and wood-burning particles that contain high mass fractions of black carbon and organic aerosol but low mass fractions of inorganic ions. Conversely, Di values are higher (~ 4) for aged carbonaceous particles containing similar mass fractions of black carbon, organic aerosol, ammonium, nitrate and sulfate. Aerosol in Paris is estimated to be 59% internally mixed in the size range 150–1067 nm, and mixing state is dependent both upon time of day and air mass origin. Daytime primary emissions associated with vehicular traffic and wood-burning result in low χ values, while enhanced condensation of ammonium nitrate on existing particles at night leads to higher χ values. Advection of particles from continental Europe containing ammonium, nitrate and sulfate leads to increases in Dα, Dγ and χ. The mixing state index represents a useful metric by which to compare and contrast ambient particle mixing state at other locations globally.

This study presents a comprehensive and critical assessment of the meteorological conditions and atmospheric flow during the Lagrangian-type "Hill Cap Cloud Thuringia 2010" experiment (HCCT-2010). HCCT-2010 was performed in September and October 2010 at Mt. Schmücke in the Thuringian forest, Germany, applying three measurements sites (upwind, in-cloud, downwind) to study physical and chemical aerosol-cloud-interactions. A Lagrangian-type hill cap cloud experiment requires suitable cloud and particularly connected airflow conditions, i.e. representative air masses at the different measurement sites. Therefore, the present study aimed at the identification of time periods during the 6-weeks duration of the campaign, where such conditions were fulfilled and which can be used in further data examinations. The following topics were studied in detail: (i) the general synoptic weather situations including the mesoscale flow conditions by means of a classification of advected air masses and calculation of non-dimensional flow parameters (e.g. Froude number), (ii) local meteorological conditions, including synoptic front passages, the presence of orographic or frontal cloudiness, cloud base heights and vertical stratification, and (iii) local flow conditions by means of statistical analyses using the quasi-inert trace gas ozone and selected size bins of particle number size distributions as well as SF6 tracer experiments in the campaign area. A comprehensive analyses using statistical measures such as the COD (Coefficient Of Divergence) and cross-correlation have been carried out for the first time in the context of a Lagrangian-type hill cap cloud experiment. Suitable criteria for the aimed statistical analyses were thus developed and applied in the present study to characterise the local flow connectivity in detail. The comprehensive examination resulted in a total of 14 so-called "Full Cloud Events" (FCE), which are shown to conform to the Lagrange-type experimental philosophy of HCCT-2010. In addition, 15 so-called "Non-Cloud Events" (NCEs) could be established, which can be used as reference cases as they provide similarly suitable flow conditions but no cloud at the summit site. Orographic cloudiness was identified for approx. one third of the FCE periods, while about two thirds were associated to synoptic fronts. The statistical flow analyses indicate the existence of a strong link between the sites during the events, particularly under constant south-westerly flow conditions, high wind speeds and slightly stable stratification. The COD analyses using continuously measured concentrations of ozone and the 49 nm diameter particle bin revealed particularly for COD values below 0.1 very consistent time series, i.e. closely linked air masses between the different sites. The cross-correlation analysis revealed under connected flow conditions typical overflow times of about 15 to 30 min between the two valley sites. Additionally, the performed SF6 tracer experiments during the campaign clearly demonstrate that under appropriate meteorological conditions a Lagrangian-type approach is valid and that the connected flow validation procedure developed in this work is suitable for identifying such conditions. Finally, an overall evaluation of the identified FCEs is presented, which provides the basis for subsequent investigations of the measured chemical and physical data during HCCT-2010.

Mass deposition fluxes of mineral dust to the tropical northeast Atlantic Ocean were determined within this study. In the framework of SOPRAN (Surface Ocean Processes in the Anthropocene), the interaction between the atmosphere and the ocean in terms of material exchange were investigated at the Cape Verde atmospheric observatory (CVAO) on the island Sao Vicente for January 2009. Five different methods were applied to estimate the deposition flux, using different meteorological and physical measurements, remote sensing, and regional dust transport simulations. The set of observations comprises micrometeorological measurements with an ultra-sonic anemometer and profile measurements using 2-D anemometers at two different heights, and microphysical measurements of the size-resolved mass concentrations of mineral dust. In addition, the total mass concentration of mineral dust was derived from absorption photometer observations and passive sampling. The regional dust model COSMO-MUSCAT was used for simulations of dust emission and transport, including dry and wet deposition processes. This model was used as it describes the AOD's and mass concentrations realistic compared to the measurements and because it was run for the time period of the measurements. The four observation-based methods yield a monthly average deposition flux of mineral dust of 12–29 ng m−2 s−1. The simulation results come close to the upper range of the measurements with an average value of 47 ng m−2 s−1. It is shown that the mass deposition flux of mineral dust obtained by the combination of micrometeorological (ultra-sonic anemometer) and microphysical measurements (particle mass size distribution of mineral dust) is difficult to compare to modeled mass deposition fluxes when the mineral dust is inhomogeneously distributed over the investigated area.

The European Metrology Research Programme participating countries and the European Union jointly fund a three year project to address the need of the automotive industry for a metrological sound base for exhaust measurements. The collaborative work on particle emissions involves five European National Metrology Institutes, the Tampere University of Technology, the Joint Research Centre for Energy and Transport and the Leibniz Institute for Tropospheric Research. On one hand, a particle number and size standard for soot particles is aimed for. Eventually this will allow the partners to provide accurate and comparable calibrations of measurement instruments for the type approval of Euro 5b and Euro 6 vehicles. Calibration aerosols of combustion particles, silver and graphite proof partially suitable. Yet, a consensus choice together with instrument manufactures is pending as the aerosol choice considerably affects the number concentration measurement. Furthermore, the consortium issued consistent requirements for novel measuring instruments foreseen to replace today’s opacimeters in regulatory periodic emission controls of soot and compared them with European legislative requirements. Four partners are conducting a metrological validation of prototype measurement instruments. The novel instruments base on light scattering, electrical, ionisation chamber and diffusion charging sensors and will be tested at low and high particle concentrations. Results shall allow manufacturers to further improve their instruments to comply with legal requirements.

Atmospheric particle number size distributions determined over 1.5 years at a central European site were statistically analyzed in terms of their relation to time of day, season, meteorology, and synoptic-scale air masses. All size distributions were decomposed into lognormal particle modes corresponding to the accumulation, Aitken, aged nucleation, and nucleation modes. The concentration of nucleation mode particles ( 30 nm) lacked such diurnal behavior, and proved to be indicative of different synoptic-scale air mass types. Over 70% of the time, air masses of Atlantic origin and maritime character prevailed, showing obvious signs of anthropogenic influence most of the time (accumulation mode: 500 cm−3; Aitken mode: 2300 cm−3). During a limited period of time (10%), however, continentally aged air with significantly enhanced concentrations of aerosol was observed (accumulation mode: 1200 cm−3; Aitken mode: 3300 cm−3). These air masses were advected from source regions in Russia, and eastern, southeastern, and central Europe, mainly under anticyclonic and high-pressure influence. The analysis provides a refined picture of the behavior of the particle number size distribution and provides parameterizations that are representative for a variety of air masses in Europe and thus suitable for future climate modeling applications.

The Aerosols99 cruise crossed the Atlantic Ocean from Norfolk, Virginia, to Cape Town, South Africa, between January 14 and February 8, 1999. The goals of the cruise were to determine the chemical, physical, and optical properties of the marine boundary layer (MBL) aerosol, the vertical distribution of aerosols and ozone, the column-integrated aerosol optical depth, and the ozone, CO, and peroxy radical chemistry in the MBL. Sampling strategies were optimized to obtain data sets to evaluate satellite-derived ocean color (Sea-viewing Wide Field-of-view Sensor), aerosol optical depth (advanced very high resolution radiometer) and total column ozone (Total Ozone Mapping Spectrometer). The cruise track crossed through seven different meteorological/oceanographic regimes ranging from background marine air masses in the Northern and Southern Hemispheres to air masses containing mineral dust and the products of biomass burning. This overview discusses the seven regimes encountered enroute and the chemical and physical properties of the MBL aerosol in each regime.

New particle formation in the polluted continental boundary layer was studied, based on 1.5-year observations of the particle size distribution, meteorological and gas phase parameters. Events of new particle formation involving significant ultrafine particle number concentrations (>104 cm−3 in the size range 3–11 nm) were observed on 20% of all days, pointing out that a frequent particle production from gaseous precursors can occur despite the relatively high pre-existing particle surface area in the area of investigation. The maximum in the observed particle size distributions was mostly above 3 nm, suggesting the actual particle nucleation to take place upwind of the measurement site. A particle growth analysis yielded 2.3±1.4 h as an upper limit of the time for the particles to grow from the critical cluster size till the observation of the peak in ultrafine number concentration. On 80% of the significant events of new particle formation (though not on all), SO2 concentrations increased considerably (by an average factor of 7), most likely by entrainment from aloft. Particle surface area was, on average, higher on event days compared to non-event days, indicating only a weak competition between condensation onto the pre-existing particle surface area and the new particle formation process. The highest statistical correlation was found between the events of new particle formation and solar radiation, indicating a high degree of meteorological control.

One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic. DOI: 10.1034/j.1600-0889.2000.00057.x

We propose an analytical expression for the relation between aerosol accumulation number and sub-micron volume over the marine boundary layer (MBL), based on a simple balance equation. By providing appropriate source and sink terms which account for entrainment, coagulation, in-cloud scavenging and condensational growth, the model is able to reproduce the observed ratio between MBL particles larger than 80 nm diameter (as a proxy for accumulation mode number) and submicron aerosol volume, from freshly polluted to background conditions. Entrainment and coagulation are essential in predicting the observed ratio. Budget and lifetime calculations show that, due to relatively low source rates of oceanic non-sea-salt-sulfate and sea-salt, the anthropogenic signature in aerosol volume remains significant even after 8 days of MBL transport.DOI: 10.1034/j.1600-0889.2000.00091.x

Aerosol light scattering and absorption properties relevant to climate change were measured as part of the Aerosol Characterization Experiment 2 (ACE-2, 15 June to 25 July 1997) at Sagres, Portugal, a site receiving anthropogenically perturbed air masses from Europe. A controlled relative humidity (RH) nephelometry system measured the dependence of the total light scattering and backscattering coefficients by particles (σsp and σbsp , respectively) upon increasing and decreasing controlled RH, maximum particle diameter (Dp) size cut, and wavelength of scattered light (λ). An aethalometer was used to measure black carbon concentrations ([BC]) to yield estimates of light absorption by particles (σap) and single scattering albedo (ω). Parameters derived from the measurements include the dependence of σsp and σbsp on RH (f(RH)), the hemispheric backscatter fraction (b), and the Angstrom exponent (A), all as functions of λ and particle Dp size cut. During polluted periods, for Dp≤10 μm, and at λ=550 nm, means and standard deviations of aerosol parameters included σsp=75.1±30.5 Mm−1 at controlled RH=27%, f(RH=82%)=1.46±0.10 and 1.22±0.06 for σsp and σbsp , respectively, and b=0.113±0.017 and 0.094±0.015 at controlled RH=27% and 82%, respectively. Transition from “clean” to polluted periods was characterized by a mean increase in σsp and σbsp by a factor of 4 to 7, increased wavelength dependence evident from an increase in A from 0.57 to 1.48, shift from 0.32 to 0.56 of the fraction of σsp from sub-micrometer Dp particles, and suppression of f(RH) by 14 to 20%. Onset of polluted periods and aerosol hygroscopic growth each resulted in ∼1% increases in ω, and an estimated range for ω at Sagres during ACE-2 was 0.91