On the Origin of AMS "cooking Organic Aerosol" at a Rural Site

A number of field observations employing aerosol mass spectrometers (AMS) have demonstrated that organic matter rich in monocarboxylic acids and aliphatic carbonyls originating from cooking activities (the COA factor) contributes significantly to ambient organic matter (OM) in urban environments. Little is known about the contribution and nature of COA in rural localities. We studied the correlation of COA with chemical tracers at a rural site in the Po Valley, Italy. Our statistical approach, based on positive matrix factorization (PMF) shows that the COA factor was clearly linked to local emissions of chloride and methanesulfonic acid (MSA), chemical tracers not associated with cooking emissions, or with combustion sources. While the association with Cl is not understood at this stage, the emission of reduced sulfur compounds, aliphatic carbonyls and monocarboxylic acids is consistent with several agricultural practices (e.g., manure storage) and waste disposal systems (e.g., landfills) which characterize the suburban and rural areas of the Po Valley and of other many populated environments. It is concluded that the nature and origins of the AMS COA factor measured at a rural site are complex and include far more than the emissions from food cooking.