New particle formation from agricultural recycling of organic waste products

Secondary organic aerosols (SOA) are a major uncertainty in climate understanding. Agriculture contributes to primary aerosol emissions, but SOA formation from gaseous precursors has not been quantified. Organic waste products such as sewage sludge are applied to cropland. Here, we show that sewage sludge is an unaccounted source of nucleation precursors, specifically skatole (C11H9N). Laboratory measurements show skatole emission and nucleation rates up to 1.1 × 10^6 cm−3 s−1 due to ozone reactivity. SO2 plays a key role in skatole oxidation and leads to intense new particle formation (NPF). We identify products of ozone reactions with skatole and discuss a possible ozonolysis mechanism. This nucleation mechanism can help explain the contribution of organic waste recycling to atmospheric aerosol balance. Based on measured particle emission fluxes, the surface area of sludge spread in France, and the incorporation time into soil, we estimate roughly one ton per year of particles generated by this activity (~0.03% of total PM10 emissions from agriculture and forestry in France). Because spreading occurs over a few days (mid-summer), these emissions may significantly affect local and regional air quality during that period.

R. Ciuraru, J. Kammer, C. Decuq, M. Vojkovic, K. Haider, Y. Carpentier, F. Lafouge, C. Berger, M. Bourdat-Deschamps, I. K. Ortega, F. Levavasseur, S. Houot, B. Loubet, D. Petitprez, C. Focsa