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Secondary organic aerosols (SOA) are one of the main sources of uncertainty in the current understanding of the Earth's climate. Agriculture contributes to primary aerosol emissions, but there is no estimate of SOA formation from gaseous precursors. Organic waste products such as sewage sludge are applied to cropland as fertilizers. In this work, we show that sewage sludge is an unaccounted source of nucleation precursors, such as skatole (C9H9N). Skatole emission and nucleation rates up to 1.1 × 106 cm−3 s−1 owing to ozone reactivity were measured in the laboratory. Our results show that SO2 plays a key role in the oxidation of skatole and leads to intensive new particle formation. The products of ozone reactions with skatole and the possible ozonolysis reaction mechanism are discussed. This nucleation mechanism might aid our understanding of the organic waste agricultural recycling contribution to the aerosol balance in the atmosphere. Based on the measured particle emission flux, the surface area of sewage sludge spread in France and the time before sewage sludge incorporation into the soil, a rough estimate of the annual quantity of particles generated by this agricultural activity is in the range of one ton, which represents ~0.03% of the total PM1.0 emissions from the agricultural and forestry sectors in France. As spreading occurs over only a few days (mid-summer), these emissions may locally be of great concern for local and regional air quality during this period of the year. [ABSTRACT FROM AUTHOR]

The intricate chemistry of the carbonaceous particle surface layer (which drives their reactivity, environmental and health impacts) results in complex mass spectra. In this respect, detailed molecular-level analysis of combustion emissions may be challenging even with high-resolution mass spectrometry. Building on a recently proposed comprehensive methodology (encompassing all stages from sampling to data reduction), we propose herein a comparative analysis of soot particles produced by three different sources: a miniCAST standard generator, a laboratory diffusion flame and a single cylinder internal combustion engine. The surface composition is probed by either laser or secondary ion mass spectrometry. Two examples of multivariate analysis, Principal component analysis and hierarchical clustering analysis proved their efficiency in both identifying general trends and evidencing subtle differences that otherwise would remain unnoticed in the plethora of data generated during mass spectrometric analyses. Chemical information extracted from these multivariate statistical procedures contributes to a better understanding of fundamental combustion processes and also opens to practical applications such as the tracing of engine emissions. [ABSTRACT FROM AUTHOR]