AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Long-Term Aerosol Mass Spectrometric Measurements in Zurich
Francesco Canonaco, JAY SLOWIK, Andre Prévôt, Urs Baltensperger, Paul Scherrer Institute
Abstract Number: 453 Working Group: Urban Aerosols
Abstract Long-term monitoring of aerosol chemical composition provides a powerful tool for investigating aerosol sources and atmospheric processing, which are critical to understanding their effects on human health, climate, and visibility. We present year-long continuous measurements of submicron aerosol composition from an aerosol chemical speciation monitor (ACSM, Aerodyne Research, Inc.) deployed in downtown Zürich, Switzerland throughout 2011. The ACSM yields quantitative mass spectra of the non-refractory aerosol component with 15 minute time resolution. These long-term measurements show a number of seasonal cycles in aerosol components. For example, particulate nitrate is much higher during the winter than in warmer seasons. Additional trends are evident in the organic spectra. Significant secondary aerosol formation from biogenic VOCs during the spring and summer months is suggested by an increase in the fraction of organic mass occurring at m/z 43 (C2H5O+ and/or C3H7+ ions) relative to the organic mass fraction at m/z 44 (CO2+, proportional to the molecular O:C ratio). Interestingly, it was observed that photochemical activity does not always increase the aerosol oxidation state. The continuous nature of the measurements also enables sampling of aerosol from unique local events, such as high levels of cooking-derived aerosol from a local festival, which might not be captured by a shorter campaign. Particle sources and processes are further investigated using positive matrix factorization (PMF) and the multi-linear engine (ME-2), which both represent the organic mass spectral time series as a linear combination of static factor mass spectra and their time-dependent intensities. ME-2 allows constraints to be placed on the factor mass spectra, which is useful for distinguishing hard-to-resolve factors. These techniques are used to evaluate the year-long importance and seasonable variability of particle sources in Zürich.