Can Positive Matrix Factorization identify sources of organic trace gases at the continental GAW site Hohenpeissenberg?

Abstract

From the rural Global Atmosphere Watch (GAW) site Hohenpeissenberg in the pre-alpine area of Southern Germany, a dataset of 24 C 2 –C 8 non-methane hydrocarbons over a period of seven years was analyzed. Receptor modeling was performed by Positive Matrix Factorization (PMF) and the resulting factors were compared to literature source profiles. Photochemical aging during transport to the relatively remote site violates the PMF prerequisite of mass conservation from source to receptor. However, previous studies showed plausible results with this method at remote sites; the applicability and restrictions of the PMF model to such a remote dataset and the influence of photochemical processing on the interpretability of the results are discussed. A six factor solution showed a high stability and the most plausible results. In addition to biogenic sources and remote sources of very stable compounds – reflecting the continental background – four additional anthropogenic factors were resolved that could be divided into two short- and two long-lived patterns from evaporative sources and incomplete combustion processes, respectively. A method to increase the uncertainty for each individual compound by including photochemical reactivity did not improve the results, but decreased the stability of the model output. The contribution of the different source categories at the site over the entire period was, in decreasing order: remote sources, long-lived evaporative sources, residential heating and long-lived combustion sources, short-lived evaporative sources, short-lived combustion sources, and biogenic sources. Despite a low overall impact, biogenic sources played an important role during summer, in particular in terms of reactivity.