Remote and still alert-eyed-aerosol research at the Sonnblick Observatory

Atmospheric aerosol particles are either emitted directly into the atmosphere (primary particles) or produced in situ through condensation of vapours formed in chemical reactions of precursor gases (new particle formation; secondary particles). Independently from the formation process atmospheric aerosol particles play an important role in respect to health issues and climatic effects.
Situated at the 3 km level, the Sonnblick Observatory generally encounters very low concentrations of particulate matter, but occasionally the observatory is also a receptor site for episodes with elevated concentration levels. These episodes can be caused by mineral (often Saharan) dust (long-range transport) or wood smoke advected from the valleys below.
A combined event of these two aerosol sources was observed at the high-altitude Sonnblick Observatory in August 2013. Evaluation of on-line aerosol measurements allowed to determine the combined and sometimes alternating influence of these emission sources. The occurrence of Saharan dust was confirmed by an increase of number concentrations of coarse particles and a negative exponent of the wavelength dependence of the single scattering albedo, determined by Nephelometer and Aethalometer measurements. During time periods less influenced by Saharan dust number concentrations of accumulation mode particles increased and a marked correlation of aerosol mass concentrations and CO mixing ratios was observed. By analyzing the wavelength dependence of the absorption coefficients determined with a seven wavelength Aethalometer the influence of the two aerosol sources was decoupled. Therefore absorption exponents of 3 and 1.3 were assumed for Saharan dust and wildfires, respectively. Mass concentrations of particulate matter caused by Saharan dust and wildfire emissions were estimated, the contribution of Saharan dust to overall particulate matter mass ranged from 5 to 80 %.
Besides episodes with elevated mass concentrations nucleation events are determined at the site. Classification of the nucleation episodes was performed for spring and early summer 2013 according to the scheme described by Del Maso et al. (2005). Occurrence of nucleation events was related to meteorological conditions prevailing at the site.
In addition to physical characterization of particulate matter the chemical characterization of aerosol samples is desirable. However, using classical methods the required sample amounts leadto longer sampling times and consequently to lower time resolution. To overcome this problem a novel approach using image-based analysis With a Horiba LabRam 800HR Raman microscope and a Quanta FEI 200 electron microscope (elemental composition investigated using energy-dispersive X-ray spectroscopy) was performed.The obtained hyperspectral images were combined into a multisensor dataset using the software package Imagelab (Epina Software Labs). Main aerosol constituents e.g. sulfates, elemental carbon and mineral particles could be identified. Based on the results from the bulk analysis, first attempts towards quantification of multisensor images of size-segregated aerosol particles could be performed for elemental carbon.