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List of Abstracts 140two mixtures of ammonium sulphate/sulphuric acid (pH ≈ 0.6, pH ≈ 2). OH radicals were produced usingtwo different methods: ozonolysis of tetramethylethylene, photolysis of methylnitrate and photolysis ofozone in the presence of nitrogen oxide. The particle phase analysis revealed the compounds with the massto charge ratios (m/z) 171, 185, 203 and 231 corresponding to terpenylic acid, pinic acid, 3-methyl-1,2,3-butanetricarboxylic acid and diaterpenylic acid acetate, respectively. The highest percentages of thesecompounds in SOA are observed in the presence of neutral particles, a dramatic decrease in mass percentageis observed with increasing particle acidity, suggesting the consumption of monomeric compounds throughacid catalysed reactions. Higher SOA yields were also observed in the presence of NO x than in the absenceof NO x . This is consistent with other monoterpene oxidation studies that the low HO x /NO ratio leads to lowerSOA yield.P-Transformation.33 ID:4264 10:30Secondary aerosol formation over urban atmosphere in the Indo-Gangetic Plain, northern IndiaKirpa Ram, Manmohan SarinPhysical Research LaboratoryContact: kirpa@prl.res.inThe chemical composition of ambient aerosols (PM2.5 and PM10) sampled during day-time (n=20) andnight-time (n=14), spread over two weeks, provides an unequivocal evidence for the formation of secondaryaerosols over an urban location (Kanpur) in the Indo-Gangetic Plain (IGP). The aerosol mass dominated byfine-mode particles (PM2.5/PM10 mass ratio = 0.46 – 0.86) and their chemical composition suggest thattotal carbonaceous aerosols (TCA = 1.6*OC + EC) account for ~50% of the PM2.5 mass; whereas massfraction of water-soluble inorganic species (WSIS) is no more than 20%. The PM2.5 mass and concentrationof carbonaceous species (EC, OC) show significant increase during night-time, indicating their efficienttrapping due to decrease in boundary layer height and/or increase in the source strength. But the averageWSOC/OC ratio is significantly higher in the day-time samples (0.66 ± 0.11) compared to that in the nighttime(0.47 ± 0.07); suggesting increased contribution of secondary organic aerosol (SOA) during day-time.The formation of particulate NO3- increases by a factor of four during night-time; whereas fractionalcontribution of SO42- shows enhancement (~20%) during day-time. The particulate NH4+ neutralizes ~85%of the acidic species (NO3- and SO42-) in PM2.5. The contribution of TCA and WSIS was maximum(~75% of PM2.5) on 30th Oct 2008, marked by a thick haze formation (also supported by MODIS data). Theformation of secondary aerosols over an urban polluted region has, thus, attracted much attention in recentyears in view of their importance in degrading the air-quality, visibility, haze formation and enhancing theaerosol absorption and scattering properties.P-Transformation.34 ID:4136 10:30Identification of higher molecular weight carboxylic acids as important components of atmosphericorganic aerosolsZoran Kitanovski, Irena GrgićLaboratory for Analytical Chemistry, National Institute of Chemistry - Ljubljana, SloveniaContact: zoran.kitanovski@ki.siWater-soluble organic compounds (WSOC) are found to be an important fraction of the total organic mass inatmospheric aerosols. It was suggested that WSOC are a mixture of polar oxygenated multifunctionalcompounds with different functional groups, like carboxylic acids as very important constituents. Studyingthe chemical diversity of the WSOC is essential for understanding the physico-chemical properties ofatmospheric organic aerosols and their role in atmospheric processes. The present study was focused mainlyiCACGP-IGAC 2010 14 July, 2010