Composition and sources of particulate matter in an industrialised Alpine valley

Abstract. A three-week long field campaign was carried out under autumnal meteorological conditions at four valley floor sites in the industrialised Swiss Rhone Valley. For one week of stable meteorological conditions, particulate matter with an aerodynamic diameter below 10 μm (PM₁₀) was analysed from daily filters using ion chromatography, X-ray fluorescence, anhydrosugars and radiocarbon analysis of the organic and elemental matter (OM and EM, respectively). Furthermore, PM₁ composition along the whole campaign was monitored in Massongex (a site near industries) by a seven-wavelength aethalometer and a quadrupole aerosol mass spectrometer (Q-AMS). At all sites, PM₁₀ secondary inorganics and non-fossil EM and OM exhibited relatively stable concentrations over the selected days. On the contrary, PM₁₀ fossil carbonaceous fractions, mineral dust components and several trace elements showed a significant decrease on Sunday, compared to the analysed working days. Their concentrations were also highly correlated. This evidenced the role of exhaust and resuspension emissions by heavy-duty vehicle traffic to the PM₁₀ concentrations along the valley.

In Massongex, organic matter and black carbon (BC) were the main contributors to PM₁ over the campaign (accounting for 45% and 18% of PM₁, respectively). An optical discrimination of BC highlighted the prevalence of fossil over wood-burning sources. Three types of PM₁ organics could be identified by factor analysis: primary wood-burning organic aerosol (P-WBOA) dominated the PM₁ carbonaceous fraction, followed by oxygenated organics (OOA) mostly representing secondary organics, and by traffic or possibly industry-related hydrocarbon-like organics (HOA) as the smallest carbonaceous contribution.

Furthermore, unusually high contributions of fine chloride were detected at all sites. They were attributed to ammonium chloride (NH₄Cl) in Massongex and represented the only significant component exclusively attributable to industrial emissions.