MSc Students Presentations - Drosatou Anthoula

Organic aerosol (OA) is a major component of atmospheric particulate matter. OA consists of thousands of mostly unknown complex relatively large (more than 5 carbon atoms) organic compounds. The complexity of OA is a result of the diverse sources and reactions of organic compounds in the atmosphere. Factor analysis of Aerosol Mass Spectrometer measurements (OA mass spectra) is often used to determine the sources of OA. In this study we aim to gain insights regarding the ability of positive matrix factorization (PMF) to separate the OA sources accurately. We performed PMF and multilinear engine (ME-2) analysis on the predictions of a state-of-the-art chemical transport model (PMCAM-SR) during a photochemically active period for specific sites in Europe in an effort to interpret the diverse factors usually identified by PMF analysis of the field measurements. Our analysis used the predicted concentrations of 27 OA components, assuming that each of them is “chemically different” from the others.
We evaluated the results of our PMF analysis of model predictions using the corresponding results of PMF of aerosol mass spectrometer ambient measurements. The PMF results based on the chemical transport model predictions are quite consistent with those of analysis of aerosol mass spectrometer measurements suggesting that this study can be used to provide insights about the factors often determined by PMF analysis of field measurements.
Initially, we investigated two of the most important primary factors reported by field studies: the hydrocarbon like OA and the biomass burning OA factor. Our analysis suggests that around 30% of the primary factor from transportation and industry is not primary material. On the other hand, we found that PMF separates clearly the biomass burning primary OA source from the rest with only a 10% error (contribution of other sources to the biomass burning factor).
One of the major questions in positive matrix factorization analysis of aerosol mass spectrometer measurements regards the sources of the two oxygenated OA (OOA) factors often reported in field studies. We found that these factors include various secondary OA compounds from a variety of anthropogenic and biogenic sources and therefore do not correspond to specific sources. Their characterization in the literature as low and high volatility factors is probably misleading because these factors have overlapping volatility distributions. However, the average volatility of the one often characterized as low-volatility factor is indeed lower than that of the other (high volatility factor). Based on the analysis of the PMCAMx-SR predictions, the first oxygenated OA factor includes mainly highly aged OA transported from outside Europe, but also highly aged secondary OA from precursors emitted in Europe. The second oxygenated OA factor contains SOA from volatile, semi-volatile, and intermediate volatility anthropogenic and biogenic organic compounds. The exact contribution of these OA components to each OA factor depends on the site.