This paper summarizes one year (April 2011 to March 2012) measurements on planar condensing surfaces of dew and rain events and related physico-chemical characteristics in the urban environment of Paris (city center). Yearly collected water was 3.48 mm for dew (63 events) and 593 mm for rain (146 events). The latter value compares well with rain data (547 mm and 107 events) collected within 12 km at Paris-Orly airport. An estimation of dew yield based on meteo data gives 235 mm and 74 events, to be compared with 17.11 mm and 196 events at Paris-Orly. These differences highlight the large reduction in dew events and dew yields in an urban area as compared to a close rural-like area. This reduction is not due to a sky view reduction but to heat island that increases air temperature and decreases relative humidity.Analysis of dew (34) and rain (77) samples were done concerning pH, electrical conductivity (EC), major anions and cations as well as selected trace metals and other minor ions. Mean pH values are found similar for both, dew (6.5) and rain (6.1), rain being slightly more acidic than dew. The mean dew total ionic content (TIC 1.8 meq/I) and EC value (124 mu S/cm) are about four times that of rain (0.45 meq/I; 35 mu S/cm), meaning that total dissolved solids in dew is nearly four times that in rain. Sulfate and nitrate are the most acidifying components, calcium the most neutralizing constituent with ratio of mean total acidity/total alkalinity comparable for dew and rain (similar to 0.9). Sulfate and nitrate have mainly anthropogenic sources, whereas chloride and magnesium are mostly connected with marine air masses. Dew is a considerable factor of wet deposition of pollutants; dew and rain ion concentrations, however, meet the WHO requirements for drinking water. (C) 2017 Elsevier B.V. All rights reserved.

The largest uncertainty in future climate predictions is caused by aerosols and clouds and their interaction with radiation. Hydrochloric acid (HCl) in the gas phase, chloride and sodium in the particle phase were measured first time with high time-resolution and simultaneously with a number of other atmospheric components (in gas, liquid and particulate phase) as well meteorological parameters during two intensive campaigns to study the phase partitioning of chlorine. To a significant extent, sea salt already is depleted in Cl in air masses reaching the west coastal site (Mace Head) of Ireland (20±10% in marine air; 46±19% in continental influenced air) and to a much higher extent (83±13%) in air masses reaching a continental station (Melpitz) in Germany caused by acid replacement by nitric and sulphuric acid

Nitrous acid and OH were measured concurrently with a number of other atmospheric components and relevant photolysis frequencies during two campaigns at the Meteorological Observatory Hohenpeissenberg (980 m a.s.l.) in summer 2002 and 2004. On most of the 26 measurement days the HNO2 concentration surprisingly showed a broad maximum around noon (on average 100 pptv) and much lower concentrations during the night (∼30 pptv). The results indicate a strong unknown daytime source of HNO2 with a production rate on the order of 2–4 × 106 cm−3s−1. The data demonstrate an important contribution of HNO2 to local HOx levels over the entire day, comparable with the photolysis of O3 and HCHO. On average during the 2004 campaign, 42% of integrated photolytic HOx formation is attributable to HNO2 photolysis.

An overview of the two FEBUKO aerosol-cloud interaction field experiments in the Thuringer Wald (Germany) in October 2001 and 2002 and the corresponding modelling project MODMEP is given. Experimentally, a variety of measurement methods were deployed to probe the gas phase, particles and cloud droplets at three sites upwind, downwind and within an orographic cloud with special emphasis on the budgets and interconversions of organic gas and particle phase constituents. Out of a total of 14 sampling periods within 30 cloud events three events (El, Ell and EIII) are selected for detailed analysis. At various occasions an impact of the cloud process on particle chemical composition such as on the organic compounds content, sulphate and nitrate and also on particle size distributions and particle mass is observed. Moreover, direct phase transfer of polar organic compound from the gas phase is found to be very important for the understanding of cloudwater composition.For the modelling side, a main result of the MODMEP project is the development of a cloud model, which combines a complex multiphase chemistry with detailed microphysics. Both components are described in a fine-resolved particle/drop spectrum. New numerical methods are developed for an efficient solution of the entire complex model. A further development of the CAPRAM mechanism has lead to a more detailed description of tropospheric aqueous phase organic chemistry. In parallel, effective tools for the reduction of highly complex reaction schemes are provided. Techniques are provided and tested which allow the description of complex multiphase chemistry and of detailed microphysics in multidimensional chemistry-transport models. (c) 2005 Elsevier Ltd. All rights reserved.

Optical methods for counting and sizing cloud droplets and a wide range of cloud water sampling methods were used to characterize the atmospheric liquid phase during the FEBUKO cloud experiments. Results near cloud base as well as more than 300m inside the hill cap clouds are presented, reflecting their inhomogeneous nature. The cloud droplet number varies from 50 to 1000cm−3 and drop sizes between 1 and 20μm diameter are most frequent. Variations in the liquid water content (LWC) and in the total ion content (TIC) are much smaller when the measurement position is deeper in the cloud. Near cloud base variability in updraft strength and, near cloud top, entrainment processes (droplet evaporation by mixing with drier air, aerosol and gas scavenging) disturb the adiabatic conditions and produce large variations in LWC and chemical composition. Six different active cloud water collectors and impactors were running side by side; they differ in the principle of sampling, in the throughput of cloudy air per unit time and in the calculated 50% cutoff diameter, which influence also their sampling efficiency. Two of them are designed to collect cloud water in two droplet size fractions. Three cloud events were selected by the FEBUKO team for detailed cloud physical and chemical analyses because they serve best the modelling demands concerning connected flow between the upwind, summit and downwind sites for process studies. Frequency distributions of the LWC and, also of the cloud base height are given as statistical parameters for both FEBUKO experiments.

Hill cap cloud field experiments were performed during autumn 2001 and 2002 in the Thüringer Wald (Germany). Gas phase trace compounds were determined at an upwind, summit, and downwind sites and major particulate components at an upwind and downwind site. Cloud water and total cloud components (drop residuals and interstitial particles) were determined at a summit site. Three events were fulfilling the criteria for the best conditions defined by during a connected flow upwind–summit–downwind sites and further detailed analysis was performed on these events. Cloud water components were compared with particle concentration at upwind and downwind site. The concentrations of non-volatile components in cloud water were found to be in good agreement with corresponding particle phase concentrations at the upwind site. Downwind site particulate component concentrations of non-volatile compounds were lower than in cloud water indicating loss processes during transport such as deposition. The concentrations of volatile components were found to be higher in cloud water than in the particle phase concentrations at up- and downwind site samples probably due to a loss from impactor sampling technique as well as a transport loss. Indications for changes of aerosol composition by cloud processes were found from a limited number of cases. Elevated sulphate and ammonium concentrations from upwind to downwind site in the smallest particle size range (PM0.05–0.14) were found during event I (20% and 17%) and event III (70% and 150%), respectively. In the particle size range of PM0.14–0.42 an increase of OC by about 20% for event I was observed. Considering the relative contributions of components to the single size range mass (avoiding physical sink processes), comparatively higher increases for sulphate, nitrate, ammonium, OC, and EC could be observed. Indications of an increase of aerosol mass can be derived in some cases from the aerosol number and volume size distributions. Results from a complex multiphase model (SPACCIM) are consistent showing an increase in concentrations of some compounds for some cases.

This contribution presents characterisation efforts of the gas phase and particle phase main components during the FEBUKO orographic cloud passage experiments in autumn 2001 and 2002 in the Thüringer 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 17μgm−3. Particles with an aerodynamic diameter up to 1.2μm 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 1.0μgm−3, whereas EC concentrations were between 0.40 and 1.0μgm−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.

The H2O2 and organic peroxides are known to be important oxidants in cloud-water, influencing the oxidising capacity of the atmosphere. Measurements of H2O2 in cloud-water have shown a wide range of concentrations depending on the season and measuring site. Moreover, organic peroxide measurements are scarce in spite of their importance. Measurements of peroxides were carried out in the Thuringian Forest, Germany, during the FEBUKO research cluster in the Fall 2001. The measuring stations were located at three sites: upwind (gas phase), summit (cloud-water and gas phase) and downwind (gas phase). Analysis was achieved by high performance liquid chromatography (enzymatic method). From the different peroxides only H2O2 was detected in the gas phase at the upwind site with mixing ratios <130ppt. In the cloud-water, besides hydrogen peroxide (H2O2), hydroxymethylhydroperoxide (HMHP), 1-hydroxyethylhydroperoxide (1-HEHP) and methylhydroperoxide (MHP) were also detected with concentrations normalised with the liquid water content up to 1.30, 0.075, 0.065 and 0.015nmolm−3, respectively. Organic peroxides (HMHP+1-HEHP+MHP) constitute up to 80% of the total peroxides during nighttime while during daytime they accounted for about 14%. Consequently, organic peroxides might play an important role in nighttime cloud chemistry.

Measurements were performed at the research site Melpitz (87m a.s.l., 51°32′N and 12°54′E), 41km north east of the Leipzig conurbation in spring 2000 to measure atmospheric nitrous and nitric acid concentrations, to compare available methods for these acids, and to investigate the distribution of particulate nitrate vs gaseous HNO3. Two different wet denuder methods were run side by side during the experiment: a wet effluent diffusion denuder (WEDD) and a rotating wet annular denuder (RWAN). The concentrations obtained for HONO with both methods agreed very well. At low relative humidity (RH) values, a good agreement was also observed for HNO3 between the two methods. However, significant differences were observed at RH values >80%. Both methods allow the measurement of atmospheric HONO and HNO3 with a fine time resolution even at very low concentration levels. Measurable daytime values for nitrous acid were observed and there were indications for heterogeneous formation. Storage of HONO or nitrite, respectively, on wet surfaces can be a source for observed daytime HONO.

Ground-based measurements were performed at the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphérique et de Transport d`Emissions” (ESCOMPTE) field site E3 (Realtor) about 30 km north of the urban environment of Marseille and east of the industrial centre Berre pond to investigate the formation of nitrous and nitric acid and to detect the distribution of reactive N-species between the gas and particle phase during photochemical pollution events. A wet denuder sampling for gases followed by a steam jet collection for aerosols was both coupled to anion chromatographic analysis. The analytical system provided data continuously with 30-min time resolution between June 13 and July 13, 2001. Indications for heterogeneous formation of nitrous acid during nighttime and daytime on ground and aerosol surfaces were found, the average HNO2/NO2 ratio was 6%. Highest concentrations were observed during two episodes of strong pollution accumulation when sea breeze transported industrial, traffic and urban pollution land-inwards. After nocturnal heterogeneous formation (about 0.1 ppbv h−1 were estimated corresponding to increasing HNO2/NO2 ratios) and accumulation processes up to 1.2 ppbv HNO2 were observed. Their photolysis produces up to 5–9×106 OH cm−3 s−1 and will contribute significantly to initiation of the daily photochemistry in the lowest part of the troposphere. For the key tropospheric species, HNO3 daily peaks up to 4 ppbv were detected.

Sampling of aerosol-nitrate can be problematic because of evaporative loss of the semi-volatile ammonium nitrate or adsorption of nitric acid gas. Such artefacts, which depend on filter type and ambient conditions, are not well documented for the filters in use in Europe and this was the reason to study these in a series of intercomparison trials. The trials were performed within the "INTERCOMP" programme of the AEROSOL subproject of EUROTRAC-2.The major effort was a 2-week field campaign at the rural site of Melpitz, a village near Leipzig in eastern Germany (INTERCOMP2000). Samplers were used containing the most common filter types in use in Europe, i.e. quartz, Teflon, (mixed) cellulose ester and cellulose. The concentration of nitrate in PM2.5, mainly present as ammonium nitrate, was on average 3.3 mugm(-3). The variability in the concentrations stemming from the samplers appeared to be rather constant: +/- 0.5 mugm(-3) from the average of all samplers. The reason for the constant (but random) variability remains unexplained. Thus, the concentrations stemming from the samplers agreed very well at the average level with relative differences of 15% and less for higher concentrations. This is evidence that the influence of the mentioned artefacts was negligible. The absence is explained by extrapolation of results of tests on the artefacts in a laboratory setting (INTERCOMP99). It was found there that the loss of ammonium nitrate from Teflon and quartz filters is only substantial when temperatures are much higher than those during the field campaign. Cellulose and cellulose-acetate filters quantitatively collected both ammonium nitrate and nitric acid in the laboratory study, but in Melpitz measured nitric acid concentrations were too low to identify its adsorption. Possible artefacts due to adsorption of nitrous acid were negligible. We also used the laboratory information to evaluate the results of a further intercomparison (INTERCOMP98) in the Po-Valley, performed at much higher temperatures than at Melpitz. We found evidence of adsorption of nitric acid by cellulose filters and evaporational loss of aerosol-nitrate from quartz filters. For the conditions encountered during the campaign we parameterised the evaporational loss in a general way as a function of temperature, as follows. There is complete evaporation at temperatures exceeding 25degreesC and full retention at temperatures less than 20degreesC. At temperatures between 20 and 25degreesC the retention is on average 50%, but with high variability.A main conclusion from this study is that under central European conditions quartz is a suitable filter material for sampling nitrate as long as the temperature does not exceed 20degreesC during sampling. Cellulose-type filters quantitatively collect aerosol nitrate and nitric acid, but negligible amounts of nitrous acid. Teflon filters were more vulnerable for evaporation losses than quartz. Indications for losses from Teflon below 10degreesC (at Melpitz) were not obtained.(C) 2004 Elsevier Ltd. All rights reserved.

The field campaign INTERCOMP2000 was organised within the EUROTRAC-2 subproject AEROSOL for characterisation of aerosol at a rural site. The groups involved used a wide range of measurement methods for aerosol particles. Although the focus was on critical aerosol properties like mass, nitrate and carbon, in this paper particular attention is given to the role of inorganic soluble material being main part of the cloud condensation nuclei. Here, we compare methods used in Europe also for inorganic ion mass concentrations: three high-volume samplers (2 Digitel and 1 Sierra Andersen, equipped with quartz fibre filters), four low-volume samplers (1 Rupprecht Patashnik with Teflon filter; 3 stacked filter units with Teflon, cellulose ester or Whatman 41 filter), and 2 low-pressure impactors (Berner type with Tedlar foils). Ten parallel 24h samples were compared. The data for the main ions nitrate, sulphate and ammonium agree well for the PM10 as well for PM2.5 aerosol fraction; relative standard deviation of about 20–40% were found. The single values for calcium, sodium and chloride which contribute only minor to the soluble inorganic mass scatter very strongly around the calculated averages: about 50% in PM10 mode, and even 100% in PM2.5 mode. While laboratory calibrations typically indicate performance close to design specifications, methods during field operation are subject to a number of sampling and handling artefacts. We know that the different sampling principles used in this study, and the analytical procedures done by each group with their own methodology will cause a main part of the observed uncertainties. In reality, due to different reasons (availability, costs, manpower, different analysis from the same sample, size and time resolution, etc) in many networks and field studies a high variability of methods for aerosol characterisation is used and often those experimental figures will be used for statistical interpretations. Thus, our paper will emphasise that harmonisation among different PM measurements is the “order of the day”.

Within the EUROTRAC-2 subproject AEROSOL, the intensive field campaign INTERCOMP2000 was conducted to compare aerosol samplers and methods to measure various aerosol properties. Here a comparison of mass concentrations measured with different PM2.5 and PM10 samplers as well as cascade impactors is described. Different filter types were used. In general, the PM2.5 and PM10 mass concentrations obtained on filters agree well. The data agree within 18.1% (PM2.5, all data). If data obtained with the TEOM (18% low) and on Whatman QM-A quartz fibre filters (low face velocity, 38% high) are excluded, PM2.5 data agree within 8.1%. For PM10, the agreement is within 6.6% (again excluding the Whatman QM-A quartz fibre filters, 22% high) or 12.1% (all data). For the impactor samples, the data agreed within 6.3% (excluding the ELPI, which was 92% high) and 8.7% for PM2.5 and PM10.

H2O2 has been attributed as tracer for the oxidation capacity of the atmosphere as well as a toxic species for plants. The dramatic increase of H2O2 concentration found in Greenland ice cores has been explained hypothetically by a negative feedback of flue gas desulphurization in Northern America and Western Europe. The idea that SO2 does play a limiting factor in atmospheric H2O2 burden, initiated an one-year highly time resolved monitoring of H2O2 in gas and rain water phase suburb of Berlin (summer 2000 till summer 2001). The diurnal and seasonal variation, in- fluences of different air masses (by using back trajectory calculations), correlation with O3 con- centration and other parameters will be presented. Together with polluted air masses H2O2 is de- clined. Evidence is shown that H2O2 is chemically produced in aqueous phase.

Frequency distributions of cloud base height and cloud type of low clouds observed between May and October 1998 at Mt. Brocken (Germany) have been derived from ceilometer measurements and synoptic observations. The summit at 1142 m a.s.l. was about 50% of that time in cloud. During daytime, Stratus clouds were the dominant cloud type (65%), whereas Cumulus clouds amounted to 27% and Stratocumulus clouds to 8%. Evidence was found that the increase of the cloud base height observed at Mt. Brocken continues since the end of the 1980s. An example for a clear anticorrelation between the liquid water content (LWC) of the cloud and the height above cloud base is shown. Other results of this detailed case study of a cloud event on October 8, 1998 concerning phase partitioning of water-soluble inorganic compounds, black carbon (BC) and organic carbon (OC) between the liquid and the interstitial phase will also be presented. The observed ion-specific increase in the solute mass per cubic meter of air with decrease of the distance between sampling position and cloud base was caused mainly by entrainment of air from the below-cloud layer. As expected, for sulfate, ammonia and nitrate, high scavenging coefficients (>0.8) were found. OC exhibits a high scavenging fraction of between 0.4 and 0.7; the value for black carbon (0.2–0.4) implies that soot was possibly to some extent internally mixed in the cloud condensation nuclei (CCN). Simultaneous measurements during a cloud event of HNO2 and HNO3 in the gas phase and N(III) and N(V) in the liquid phase were made for the first time.

Gas-phase H2O2, organic peroxides and carbonyl compoundswere determined at various sites from Mid-July to early August 1998 during the BERLIOZ campaign in Germany. The sites were located northwest of Berlin and were chosen to determine pollutants downwind of the city emissions during a summer smog episode. Hydrogen peroxide (H2O2),methyl hydroperoxide (MHP, CH3OOH) and occasionally hydroxymethyl hydroperoxide (HMHP, HOCH2OOH) were quantified in air samples by commercial fluorimetric methods and classical HPLC with post-column derivatisation by horseradish peroxidase/p-hydroxyphenyl acetic acid and fluorimetric detection. Carbonyl compounds were determined in ambient air by a novel method based onO-pentafluorobenzyl hydroxylamine as derivatisation agent.Mixing ratio profiles of the hydroperoxides and the carbonyl compounds are reported for the intensive phase of the campaign, 20–21 July, 1998. Peroxides showed pronounced diurnal variations with peak mixing ratios in the early afternoon. At times, a second maximum was observed in the late afternoon. The major part of the H2O2 was formed throughrecombination reactions of HO2 radicals, but there is some evidencethat H2O2 is also formed from ozonolysis ofanthropogenic and/or biogenic alkenes. Diurnal variations of mixing ratios of various carbonyl compounds are reported: alkanals (C2 to C10,isobutanal), unsaturated carbonyl compounds (methacrolein, methylvinylketone, acrolein), hydroxycarbonyl (glycolaldehyde, hydroxyacetone) and dicarbonyl compounds (glyoxal, methylglyoxal, biacetyl), aromatic compounds (benzaldehyde, o- and m-tolylaldehyde) and pinonaldehyde.