Comparison of real time measurements by FIGAERO CIMS and AMS from biogenic SOA formation in the CLOUD chamber.

Abstract:

Highly oxygenated molecules from the ozonolysis of α-pinene have been seen to nucleate and form new particles in the atmosphere. The composition of these particles is affected by kinetics and thermodynamics, the effects of which are highly dependent on the temperature where these particles are formed. Here we present results from pure biogenic nucleation at several temperatures ranging from +5 to -50 degrees Celsius at the CLOUD chamber at CERN, that the temperature affects the composition of particles formed and further work to show physical relevance of these chemical differences by comparing data collected by two mass spectrometers in real time. The aerosol mass spectrometer (AMS) quantitatively measures the bulk composition of particles, while the Filter Inlet for Gases and AEROsols (FIGAERO) with an iodide chemical ionization mass spectrometer can provide aerosol molecular information. With positive matrix factorization (PMF) of AMS data we show different factors dominate the composition of the particles at high temperature and at low temperature. The most highly oxygenated products are associated with the particles formed at high temperatures, while the least oxidized products are selected for at low temperatures. By coupling these results with the thermograms of the FIGAERO we can understand the chemistry that bulk AMS data misses. PMF of thermograms provides valuable information in terms of volatility of the products and greatly expands our understanding of the factors seen in the AMS data.