Photochemical formation and microphysics of aerosols from real plant emissions

By emission of volatile organic compounds (VOC) which on oxidation form secondary organic aerosols (SOA) the vegetation is coupled to atmosphere and climate. We investigated new particle formation from tree emissions in a new setup: a plant chamber housing the trees coupled to a reaction chamber for oxidizing the plant emissions and for forming SOA (Julich Plant Aerosol Atmosphere Chamber, JPAC). Boreal, temperate Midlatitude, and Mediterranean tree species were studied and α-pinene was used as reference compound to characterize the specifics of JPAC and to study humidity and OH dependence of new particle formation. The strength and the pattern of the tree emissions were varied by increasing the temperature for the plants, thus mimicking the higher frequency of occurrence of warmer days in a future climate. Under the experimental conditions OH radicals were essential for inducing new particle formation, although O3 (≤ 80 ppb) was always present and a part of the monoterpenes and the sesquiterpenes reacted already with ozone before OH was generated. Formation rates of 3 nm particles were linearly related to the carbon mixing ratios of the VOC, as were the maximum observed volume and the condensational growth rates. The threshold of new particle formation was lower for the tree emissions than for α-pinene. Hygroscopic growth factors and activation to cloud droplets were measured to characterize climate relevant properties of the resulting aerosols. Overall the hygroscopic properties of the biogenic SOA from the highly mixed tree emissions are similar to those found for individual monoterpenes and sesquiterpenes. However, changes of emission pattern from species to species or induced by heat stress is reflected in the hygroscopic properties of the resulting SOA. The biogenic SOA revealed close to ideal Kohler behavior with significantly reduced surface tension at activation compared to pure water. Be and Cl interlaboratory comparisons: Implications for terrestrial production rates? S. MERCHEL, W. BREMSER, V. ALFIMOV, M. ARNOLD, G. AUMAITRE, L. BENEDETTI, D.L. BOURLES, R. BRAUCHER, M. CAFFEE, M. CHRISTL, L.K. FIFIELD, R.C. FINKEL , S.P.H.T. FREEMAN, A. RUIZ-GOMEZ, P.W. KUBIK, D.H. ROOD, K. SASA, P. STEIER, S.G. TIMS, A. WALLNER, K.M. WILCKEN AND S. XU CEREGE, 13545 Aix-en-Provence, France FZD, 01314 Dresden, Germany (s.merchel@fzd.de) BAM, 12489 Berlin, Germany ETH, 8093 Zurich, Switzerland PRIME Lab, Purdue University, IN 47906, USA ANU, Canberra, ACT 0200, Australia CAMS, LLNL, Livermore, CA 94550, USA SUERC, East Kilbride G75 0QF, UK CNA, University of Seville, 41092 Sevilla, Spain University of Tsukuba, Ibaraki, 305-8577, Japan VERA, Faculty of Physics, U Wien, 1090 Wien, Austria