Carbonaceaous Aerosol Components: Chemical Composition, Reactivity, and Hygroscopicity (CARBAERO)

Funding: BMBF-AFO2000 (Nachwuchsgruppe)

 

Introduction

The influence of aerosols on atmospheric chemistry and physics, climate and public health is one of the central topics in today's environmental research. Besides the aerosol particles’ size distribution their chemical composition is the primary parameter governing heterogeneous and multiphase chemical reactions in the atmosphere, formation of clouds and precipitation, radiative climate forcing effects, and health effects of aerosols. Several studies have shown that carbonaceous components are major constituents of tropospheric aerosols (10-50 % mass fraction), that black carbon is the main light absorber in air particulate matter, and that organics can strongly affect the physicochemical particle properties. The actual composition of atmospheric particles is, however, spatially and temporally highly variable, and in particular carbonaceous components have been characterized only sparsely and incompletely up to now (e.g. Pöschl et al., 2002; Pöschl et al., 2003a; and references therein). Therefore the project CARBAERO, which is part of the German Atmospheric Research Program 2000 (AFO2000), is aimed at characterizing the molecular structures and abundances, reactivity and water vapor interactions of carbonaceous aerosol components. The investigations are focused primarily on aromatic compounds, macromolecules (biopolymers and humic-like substances), and elemental carbon, and the following key questions are addressed:

1) What are the effects of carbonaceous aerosol components on the physico-chemical properties of  atmospheric particles, on their interaction with reactive trace gases, water vapour, clouds, and precipitation, and thus on their influence on climate and public health?

2) How is the composition of carbonaceous aerosol components changed by chemical aging (reaction products and kinetics), and how can these processes be efficiently described in atmospheric models?

 

Activities and Results

Since the project start in July 2000 extensive research activities have been pursued and scientific results have been achieved in the following areas:

1) Development and optimization of analytical methods for the determination of polycyclic aromatics, carbohydrates, proteins, and humic-like substances in atmospheric aerosol samples (extraction schemes; chromatographic, spectroscopic, and thermochemical methods; enzymatic assays; Franze et al., 2003; Schaller et al., 2003; Schauer et al., 2003a).

2) Field measurement campaigns at urban/suburban, rural/alpine and high alpine locations (Munich, Hohenpeiussenberg, Zugspitze): observation of characteristic differences in the physical properties (particle number and mass concentration and size distribution) and chemical composition (total/elemental carbon TC/EC, polycyclicl aromatic hydrocarbons and nitro-derivatives PAH/Nitro-PAH, proteins, amino acids; Franze et al., 2003; Schaller et al., 2003; Schauer et al., 2003a; Zerrath et al., 2003).

3) Aerosol flow tube experiments on the interaction of spark-discharge soot particles (with/without PAH-coating) with reactive trace gases (O3, NO2) and water vapor: reaction kinetics and products (Pöschl et al., 2001; Schauer et al., 2003b)

4) Investigation of the hygroscopic growth and microphysical restructuring of aerosol particles with complex chemical composition upon interaction with water vapor (HTDMA-experiments with mixtures of biopolymers and inorganic salts; Mikhailov et al., 2003a; 2003b).

5) Development of a kinetic model framework for aerosol surface chemistry and gas-particle interactions (Ammann et al., 2003; Pöschl et al., 2003).

 

References

Ammann, M., Pöschl, U., & Rudich, Y. (2003). Effects of reversible adsorption and Langmuir-Hinshelwood surface reactions on gas uptake by atmospheric particles, Phys. Chem. Chem. Phys., 5, 351-356.

Franze, T., Krause, K., Niessner, R., & Pöschl, U. (2003). Proteins and amino acids in air particulate matter, EAC 2003, Madrid.

Mikhailov, E., Vlasenko, S., Niessner, R., & Pöschl, U. (2003a). Interaction of aerosol particles composed of protein and inorganic salts with water vapor: hygroscopic growth and microstructural rearrangement, EAC 2003, Madrid.

Mikhailov, E., Vlasenko, S., Niessner, R., & Pöschl, U. (2003b). Interaction of aerosol particles composed of protein and inorganic salts with water vapor: hygroscopic growth and microstructural rearrangement, to be submitted to Atmospheric Chemistry and Physics.

Pöschl, U. (2002). Formation and decomposition of hazardous chemical components contained in atmospheric aerosol particles, Journal of Aerosol Medicine, 15, 203-212.

Pöschl, U. (2003). Aerosol particle analysis: challenges and progress, Analytical and Bioanalytical Chemistry, 375, 30-32.

Pöschl, U., Letzel, T., Schauer, C., & Niessner, R. (2001). Interaction of ozone and water vapor with spark discharge soot aerosol particles coated with benzo[a]pyrene: O3 and H2O adsorption, benzo[a]pyrene degradation and atmospheric implications, Journal of Physical Chemistry A, 105, 4029-4041.

Pöschl, U., Rudich, Y., & Ammann, M. (2003). Kinetic model framework for aerosol surface chemistry and gas-particle interactions, to be submitted to Atmospheric Chemistry and Physics.

Schaller, U., Zerrath, A., Niessner, R., & Pöschl, U. (2003). Analysis of carbohydrates, humic-like substances and elemental carbon in air particulate matter, EAC 2003, Madrid.

Schauer, C., Niessner, R., & Pöschl, U. (2003a). Polycyclic aromatic hydrocarbons in urban air particulate matter: decadal and seasonal trends, chemical degradation and sampling artefacts, submitted to Environmental Science & Technology.

Schauer, C., Niessner, R., & Pöschl, U. (2003b). Chemical reactivity of polycyclic aromatic hydro­carbons on aerosol particles: field measurements and laboratory experiments, EAC 2003, Madrid.

Schauer, C., Niessner, R., & Pöschl, U. (2003). Polycyclic aromatic hydrocarbons (PAH) and Nitro-PAH in urban, rural, and alpine aerosols: local differences, decadal and seasonal trends, and sampling artefacts, EAC 2003, Madrid.

Zerrath, A., Niessner, R., & Pöschl, U. (2003). Physical and chemical characterisation of atmospheric aerosols with an electrical low pressure impactor, EAC 2003, Madrid.

 

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