Anne Kasper-Giebl

Source apportionment of PM2.5 organic aerosol over Europe: Primary/secondary, natural/anthropogenic, and fossil/biogenic origin

On the basis of a 2-year comprehensive data set obtained within the CARBOSOL project, seasonal source apportionment of PM2.5 aerosol is attempted for five rural/remote sites in Europe. The approach developed combines radiocarbon measurements with bulk measurements of organic carbon (OC), elemental carbon (EC), and two organic tracers ( levoglucosan and cellulose). Source types are lumped into primary emissions from fossil fuel combustion and biomass burning, bioaerosol, and secondary organic aerosol from precursors emitted by fossil and nonfossil sources. Bulk concentration ratios reported for these source types in the literature are used to estimate the source contributions which are constrained by measured radiocarbon concentrations. It has been found that while fossil-related sources predominate EC throughout the year at all sites, the sources of OC are primarily biogenic and markedly different between summer and winter. In winter biomass burning primary emission is the main source, with sizable additional contribution from fossil fuel combustion. In contrast, in summer secondary organic aerosol (SOA) from nonfossil sources becomes predominant (63-76% of TC), with some contribution of SOA from fossil fuel combustion. The results agree well with recent findings of other authors who established the predominance of biogenic SOA for rural sites in summer in Europe. An uncertainty analysis has been conducted, which shows that the main conclusions from this study are robust.

Levoglucosan levels at background sites in Europe for assessing the impact of biomass combustion on the European aerosol background

Atmospheric levoglucosan has been determined as a proxy for “biomass smoke” in samples from six background stations on a west–east transect extending from the Atlantic (Azores) to the mid-European background site KPZ (K-Puszta, Hungary). Concentration levels of levoglucosan (biannual averages) in the west–east transect range from 0.005 μg/m3 at the oceanic background site AZO (Azores) to 0.52 μg/m3 at AVE (Aveiro, Portugal). The atmospheric concentration of “biomass smoke” (biannual averages) was derived from the levoglucosan data with wood-type-specific conversion factors. Annual averages of wood smoke levels ranged from 0.05 μg/m3 at AZO to 4.3 μg/m3 at AVE. Winter (DJF) averages at the low-level sites AVE and KPZ were 10.8 and 6.7 μg/m3, respectively. Relative contributions of biomass smoke to organic matter (OM) range from around 9–11% at the elevated sites SIL, PDD and SBO, as well as for AZO, to 36% at the low-level site AVE and 28% at KPZ. Surprisingly high relative concentrations of biomass smoke in OM (68 and 47%) were observed for wintry conditions at the continental low-level CARBOSOL sites AVE and KPZ. Thus biomass smoke is a very important constituent of the organic material in the mid and west European background with summer contributions to organic matter of around 1–6% and winter levels of around 20% at the elevated mountain sites and 47–68% at rural flat terrain sites, not including secondary organic aerosol from biomass combustion sources.

The contribution of bacteria and fungal spores to the organic carbon content of cloud water, precipitation and aerosols

To estimate the contribution of bacterial and fungal carbon to the carbon content of atmospheric samples, the number concentrations of bacteria and fungal spores in cloud water, snow, rain and aerosol samples collected at a continental background site in the Austrian Alps were determined. Based on these number concentrations, bacterial and fungal carbon was calculated and related to the total carbon (TC) and organic carbon (OC) contents of the samples. In cloud water samples, an average of4.5 x 10 3 spores ml -1 was found, which corresponds to 1.5% of OC. The average bacterial abundance was 2.0 × 10 4 cells ml -1 corresponding to 0.01% ofOC. In snow samples, the average concentrations of bacteria and fungi were 3.1 x 10 3 cells ml -1 corresponding to 0.015% of TC and 6.2 x 10 2 spores ml -1 corresponding to 1.8% of TC, respectively. In aerosol samples, average concentration of bacteria amounted to 1.2 x 10 4 cells m -3 , which corresponds to 0.03% of OC, while fungal concentrations averaged to 7.3 x 10 2 spores m -3 3 or 0.9% ofOC. As fungal spores occur predominantly in the size range > 2.1 μm aerodynamic equivalent diameter (a.e.d.), their contribution to the coarse size fraction (2.1-10 μm) was investigated and amounted up to 9.9% ofOC.

Climatology of aerosol composition (organic versus inorganic) at nonurban sites on a west‐east transect across Europe

in central Europe. Aerosols were analyzed for 210 Pb, inorganic ions, elemental (EC) and organic (OC) carbon, water soluble organic carbon (WSOC), macromolecular type (humic-like) organic substances (HULIS), C2–C5 diacids, cellulose, and levoglucosan. Pooled aerosol filters were also used for the identification of different families of organic compounds by gas chromatography/mass spectrometry, GC/MS, as well as 14 C determinations. The data resulted in a climatological overview of the aerosol composition over Europe in the various seasons, from west to east, and from the boundary layer to the free troposphere. The paper first summarizes the characteristics of the sites and collected samples and then focuses on the aerosol mass partitioning (mass closure, inorganic versus organic, EC versus OC, water soluble versus insoluble OC), giving an insight on the sources of carbonaceous aerosol present in rural and natural background areas in Europe. It also introduces the main role of other companion papers dealing with CARBOSOL aerosol data that are also presented in this issue.

Seasonal trends and possible sources of brown carbon based on 2-year aerosol measurements at six sites in Europe

Brown carbon is a ubiquitous and unidentified component of organic aerosol which has recently come into the forefront of atmospheric research. This component is strongly linked to the class of humic-like substances (HULIS) in aerosol whose ultimate origin is still being debated. Using a simplified spectroscopic method the concentrations of brown carbon have been determined in aqueous extracts of fine aerosol collected during the CARBOSOL project. On the basis of the results of 2-year measurements of several aerosol constituents at six European sites, possible sources of brown carbon are inferred. Biomass burning ( possibly domestic wood burning) is shown to be a major source of brown carbon in winter. At elevated sites in spring, smoke from agricultural fires may be an additional source. Direct comparison of measured brown carbon concentrations with HULIS determined by an independent method reveals that the two quantities correlate well at low-elevation sites throughout the year. At high-elevation sites the correlation is still high for winter but becomes markedly lower in summer, implying different sources and/or atmospheric sinks of brown carbon and HULIS. The results shed some light on the relationships between atmospheric brown carbon and HULIS, two ill-defined and overlapping components of organic aerosol.

Origin of C2–C5 dicarboxylic acids in the European atmosphere inferred from year‐round aerosol study conducted at a west‐east transect

[1] An atmospheric study of C 2 -C 5 dicarboxylic acids was conducted over two years at seven sites located from the Azores to eastern continental European sites. The lowest concentrations of total C 2 -C 5 diacids are observed at the Azores (Portugal) and at 4360 m elevation in the Alps (∼50 ng m -3 ), and the highest (400 ng m -3 ) are observed at the rural K-puszta site (Hungary). Quasi-absent at surface sites, the seasonal cycle of total diacids is characterized by a pronounced summer maximum at elevated sites, the highest summer level (510 ng m -3 ) being observed at the forested mountain site of Schauinsland (Germany). Whatever site and season, oxalic acid is always the most abundant diacid with a relative abundance higher than 60%. The climatology of C 2 -C 5 diacids in Europe is discussed versus environmental conditions at sites (marine/ continental, rural/forested, boundary layer/free troposphere, and winter/summer). Observations are used to discuss the possible sources of C 2 -C 5 diacids, with special emphasis on their primary versus secondary and natural versus anthropogenic origin. At surface sites in winter, fast secondary productions in wood burning plumes in addition to secondary production from volatile organic carbon (VOC) species emitted by vehicles seem to be important contributors. In summer the impact of anthropogenic sources is weakened and biogenic emissions from vegetation (unsaturated fatty acids, isoprene, oxygenated VOCs, and eventually monoterpenes) likely represent major precursors of diacids. At the Azores, diacids are not only related to long-range transport from continents but also to marine biogenic emissions from phytoplankton, particularly in summer.

Formic, acetic, oxalic, malonic and succinic acid concentrations and their contribution to organic carbon in cloud water

The carbon content of cloud water at a continental background site in Austria was studied during two intensive field campaigns in spring 1999 and 2000. Six carboxylic acids, total (TC) and black (BC) carbon as well as major inorganic ions were determined. Organic carbon (OC) was calculated as the difference between TC and BC. The most abundant carboxylic acids were acetic (average: 0.93 μg ml−1) and formic (0.61) followed by oxalic (0.38), succinic (0.15) and malonic (0.20) acids. Pyruvic acid was below the detection limit (<0.08) in all samples. The BC concentration was 1.15 and OC 4.81 μg ml−1 on average. Relating carboxylic acid concentrations to OC, the monocarboxylic acids alone represent 9.3% of OC. Adding the dicarboxylic acids, this average value increases to 11%. Although they are major components, no general trend could be seen between carboxylic acid and OC concentrations.

CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter

Abstract The cloud droplet activation of monodisperse laboratory aerosols consisting of single organic and inorganic substances as well as a mixture of several substances was investigated using the University of Vienna cloud condensation nuclei counter (CCNC). The CCNC operates on the principle of a static thermal diffusion chamber. Water vapour supersaturations can be set in the range from 0.1% to 2%. Aqueous solutions of oxalic acid and malonic acid as well as solutions of inorganic compounds (NaCl and (NH4)2SO4) were nebulized in a Collison atomizer and then passed through a closed-loop differential mobility particle spectrometer to produce monodispersed particles. An internally mixed aerosol consisting of ammonium sulphate, oxalic acid and malonic acid with relative concentrations resembling those found in cloud water at a mountain station [Loflund, Kasper-Giebl, Schuster, Giebl, Hitzenberger, Reischl et al. (2002) Atmos. Environ. 36, 1553] was also investigated for cloud condensation nuclei (CCN) activation. All these particles were activated at supersaturations expected from Kohler theory. Oxalic and malonic acid particles are therefore expected to be good atmospheric CCN both as pure particles and as internally mixed particles containing other chemical compounds.

Scavenging Efficiency of ‘Aerosol Carbon’ and Sulfate in Supercooled Clouds at Mt. Sonnblick (3106 m a.s.l., Austria)

Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and ‘aerosol carbon’ to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (εSO) ranged from 0.52 to 0.99 with an average of 0.80. ‘Aerosol carbon’ was scavenged less efficiently with an average value (εAC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both εSO and εAC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, εSO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of ≈ 0.3 g/m3. In the case of ‘aerosol carbon’, we obtained a more gradual increase of εAC up to an LWC of ≈ 0.5 g/m3. At higher LWCs, ε_ remained relatively constant at 0.60. As the differences between εSO and εA varied across the LWC range observed at SBO, we assume that part of the ‘aerosol carbon’ was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior.

Black carbon and other species at a high‐elevation European site (Mount Sonnblick, 3106 m, Austria): Concentrations and scavenging efficiencies

During a recent measurement project, several intensive campaigns were performed on Mount Sonnblick (3106 m above sea level) in the Austrian central range of the Alps. Cloud water and interstitial aerosol samples were obtained from supercooled clouds by using a specially designed cloud water sampler [Kruisz et al., 1993]. The samples were analyzed for black carbon (BC) by an optical technique (integrating sphere [Hitzenberger et al. 1996]) using liquid samples, for major inorganic ions by ion chromatography and for total carbon (TC) by a combusion method. During the fall campaign of 1996, cloud water BC concentrations ranged from 0.45 to 3.64 μg/mL (average concentration 0.85 μg/mL). During the spring 1997 campaign, cloud water BC concentrations ranged from 0.55 to 2.95 μg/mL (average concentration 1.07 μg/mL). The dominant ion in cloud water was SO42− with concentrations from 0.36 to 86.5 μg/mL (average 6.83 μg/mL) in fall 1996 and 0.31–15.4 μg/mL (average 3.06 μg/mL) in spring 1997. In the individual samples, the BC/SO42− ratio ranged from 0.036 to 1.2 (average 0.316) in fall 1996 and 0.036 to 2.04 (average 0.79) in spring 1997. The extreme values were usually confined to short periods within one cloud event. Scavenging efficiencies e were calculated by using cloud water and interstitial aerosol concentrations from samples obtained simultaneously with the cloud water sampler for the 1997 campaign. For BC, eBC = 0.74 (±0.19) was found, while the values for SO42− and TC were eSO4 = 0.91 (±0.08) and eTC = 0.57 (±0.21), respectively. The findings of an earlier study [Kasper-Giebl et al., 2000], where eSO4 depended on the liquid water content, were confirmed here for all the three substances.