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Organic nitrates (ON) are known to be present in secondary organic aerosol and act as a reservoir of nitrogen oxides, regulating the local and regional ozone and hydroxyl radical budgets. This work reports observations of particulate ON in Finnish remote boreal forest at a site with dominant emissions from biogenic volatile organic compounds. High Resolution-Aerosol Mass Spectrometer data were analysed in a unique way to characterize the sources of inorganic and organic nitrates. ON were found to be related to local sources with semi-volatile properties. Also they were implying a nocturnal formation mechanism. Occasionally, local sawmill emissions contributed greatly to the organic nitrates. The observations indicated that in the remote boreal forest area the NO3 radicals are oxidizing biogenic VOCs producing ON. This work demonstrates the significant impact of anthropogenic-biogenic emissions interaction on the atmospheric organic nitrate aerosol mass concentration. [ABSTRACT FROM AUTHOR]

Measurements of aerosol chemical and hygroscopic properties and cloud condensation nuclei were carried out as a part of the third Pallas Cloud Experiment. In this study, the aerosol hygroscopicity parameter, κ, was determined using data from instruments operating in the sub-saturated and supersaturated water vapour regimes, as well as from measurements of aerosol chemical composition. During the campaign, κ varied from ~0.01 to ~0.37 as derived by Cloud Condensation Nuclei counter and Hygroscopic Tandem Differential Mobility analyser data, and from ~0.13 to ~0.60 as derived from Aerosol Mass Spectrometer data, the average values being 0.11 and 0.29, respectively. CCN closure calculations showed that the sub-saturated growth factor retrieved CCN concentration is lower than the measured one. Overall, at the Pallas site, aerosol hygroscopicity was size dependent with hygroscopicity increasing with size. Hence, size dependent information on composition is needed to predict CCN concentrations relevant to cloud droplet formation. [ABSTRACT FROM AUTHOR]

Organic compounds can enhance the hygroscopic properties of insoluble dust particles and thereby affect their cloud condensation nuclei activity in the atmosphere. In this study, Arizona Test Dust (ATD) particles were exposed to oxidized organic vapors from the ozonolysis of α-pinene in a laboratory chamber. The particle size-dependent morphology, inorganic and organic composition and hygroscopic properties were studied. The dust consisted of particles with a range of morphologies from spherical to geometrical, with a size range from 50 nm to 1 µm. Exposure to oxidized organics resulted in a separate mode of secondary organic aerosol (SOA) particles with size ranging below 100 nm and a well-mixed ATD + SOA mode at larger sizes. The O:C mole ratio for the organics produced from α-pinene ozonolysis was stable at 0.4 ± 0.05 in all experiments. The results showed that the hygroscopicities of the ATD particles with a diameter of 100-150 nm were enhanced by a factor of four with the addition of SOA, corresponding to a particulate organic volume fraction of ~0.6 and an average κ of 0.09. [ABSTRACT FROM AUTHOR]

In this study, we compare new particle formation (NPF) in the boundary layer at different sites in Europe: Melpitz, Germany (central Europe), San Pietro Capofiume, Italy (southern Europe) and Hyytiälä, Finland (northern Europe) for the period of two years (July 2003 June 2005). NPF was studied based on observations of the particle size distribution, meteorological and gas phase parameters. Nucleation was found to occur frequently at all stations, however seasonal differences were observed for every station. These differences have a cleat- correlation with the annual variation of estimated formation rate values. The growth rate reached its maximum values during summer at all three stations. In Hyytiälä the formation and growth of the particles was characterized by low pre-existing condensation sink and most likely high biogenic VOC concentrations associated with the growth season, and in Melpitz and San Pietro Capofiume by the high level of pollution arriving from the nearby industrial and agricultural sources. [ABSTRACT FROM AUTHOR]