Increased PM Concentrations during a Combined Wildfire and Saharan Dust Event Observed at High-Altitude Sonnblick Observatory, Austria

Gerhard Schauer,Gris?a Moc?nik,Anne Kasper-Giebl

doi:10.4209/aaqr.2015.05.0337

Abstract

A period of increased particulate matter concentrations was observed at the high-altitude Sonnblick Observatory in August 2013. Trajectory analysis, wildfire maps and the evaluation of aerosol measurements revealed a combined and sometimes alternating influence of long-range transport of Saharan dust and emissions of wildfires. The occurrence of Saharan dust was confirmed by an increase of coarse particle number concentration and a negative exponent of the single scattering albedo wavelength dependence, determined by Nephelometer and Aethalometer measurements. During time periods less influenced by Saharan dust, number concentration 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, with the contribution of Saharan dust to overall particulate matter mass ranging from 5% to 80%.

Highlights

The great potential of mountain observatories to be used as platforms for monitoring background concentrations of aerosolized particulate matter and atmospheric trace gases is well documented (e.g., Galasyn et al, 1987; Kasper and Puxbaum, 1998; Nyeki et al, 1998)
Elevated concentrations were determined in the time period from August 3 to August 9, 2013, when the average mass concentration increased to 22.4 μg m–3
The analysis of a combined event of long range transport of Saharan dust and particulate matter originating from wildfires allowed us to distinguish the contributions of the two aerosol sources

Summary

Introduction

The great potential of mountain observatories to be used as platforms for monitoring background concentrations of aerosolized particulate matter and atmospheric trace gases is well documented (e.g., Galasyn et al, 1987; Kasper and Puxbaum, 1998; Nyeki et al, 1998). Regional or long range transport can lead to elevated concentration levels. Long range transport of Saharan dust and its climatology are well documented (Collaud Coen et al, 2004). The Sahara is the most powerful source for the emission of soil dust in the world (Swap et al, 1996; Goudie and Middleton, 2001) and transport to Europe is observed regularly (Stuut et al, 2009; Su and Toon, 2011). The transport of Saharan dust to Europe and especially the high Alpine regions has been addressed long ago (Wagenbach et al, 1989; DeAngelis and Gaudichet, 1991). A review about the occurrence and implications of Saharan dust storms and subsequent long range transport of soil dust is given by Goudie and Middleton (2001). Saharan dust events lead to PM concentrations above the existing regulatory limit values in the Mediterranean region (Matassoni et al, 2009; Salvador et al, 2013)

Methods

Results

Conclusion