Chemical and Source Characterization of Submicron Particles at Residential and Traffic Sites in the Helsinki Metropolitan Area, Finland

Abstract

Chemical characterization of non-refractory submicron particles (NR-PM 1 ) and source apportionment of organic aerosols (OA) were carried out at four different sites in the Helsinki metropolitan area, Finland, using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM). Two of the sites represented suburban residential areas, whereas the other two were traffic sites, one in a curbside in downtown and the other one in a suburban highway edge. The residential and the curbside measurements were conducted during the winter, but the highway campaign was carried out in the autumn. NR-PM 1 were composed mainly of organics (40-68% in the different sites), followed by sulphate (11-34%), nitrate (12-16%), ammonium (7.8-8.5%) and chloride (0.24-1.3%). The mean concentrations of NR-PM 1 were quite similar during the winter campaigns (10.1-12.5 µg/m 3 ), but NR-PM 1 was clearly lower during the autumn campaign at the highway site (6.0 µg/m 3 ) due to the meteorology (favourable mixing conditions), small concentrations of long-range transported particles and non-intensive heating period locally and regionally. Using a multilinear engine algorithm (ME-2) and the custom software tool Source Finder (SoFI), the organic fraction was divided into two or three types of OA representing hydrocarbon-like organic aerosol (HOA), oxygenated organic aerosol (OOA), and in three sites, biomass burning organic aerosol (BBOA). At the downtown traffic site (Curbside), BBOA could not be found, probably because most of the local wood burning occurs in the suburban areas of the Helsinki region. OOA had the largest contribution to OA at all the sites (50-67%). The contribution of HOA was higher at the traffic sites (25-32%) than at the residential sites (15-18%). At the suburban residential and highway sites, the contribution of BBOA was high (25-30%). Especially during cold periods, very high BBOA contributions (~50%) were observed at the residential sites.

Chemical and physical characterization of traffic particles in four different highway environments in the Helsinki metropolitan area

“…The speed limit on Ring I was 80 km h −1 . The Helsinki Region Environmental Services Authority (HSY) had an air quality monitoring station at Malmi, and the chemical composition and sources of PM 1 at this site have been discussed earlier in Aurela et al (2015).…”

Applications and limitations of constrained high-resolution peak fitting on low resolving power mass spectra from the ToF-ACSM

“…A collection efficiency of 0.5 was assumed based on previous studies conducted on SMEAR III station, e.g. Aurela et al (2015). During the measurement period presented here the PM concentrations exhibited a mean average of 16.2 µg m −3 .…”

“…The limited mass resolving power of the ETOF-equipped ToF-ACSM precludes the calculation of the oxidation state (see Kroll et al, 2011) and O / C and H / C ratios using the elemental analysis approach commonly employed in HR-ToF-AMS analysis and detailed in Aiken et al (2007) and Canagaratna et al (2015). However, it was recently shown that molecular and bulk chemical information can be extracted from series of complex mass spectra with limited mass resolution using a method developed by Stark et al (2015).…”

“…To support the validity of this method, the estimated oxidation state value was also analogously calculated from spectra generated for a range of organic standards using the data presented in Canagaratna et al (2015). For each compound, synthetic ETOF spectra were created by convolving a typical ETOF transfer function with the list of fitted ions and their intensities from the HR-ToF-AMS peak-fitting results of Canagaratna et al (2015). The estimated oxidation state calculated from these spectra is compared to the values calculated from the elemental composition in Fig.…”

Developments in Unipolar Charging of Airborne Particles: Theories, Simulations and Measurements

“…Airborne particles consist of diverse composition including nitrates, sulfates, elemental and organic carbon, polycyclic aromatic hydrocarbons (PAHs), biological compounds, and metals (Cheruiyot et al, 2015;Kim et al, 2015), which causes severe impacts on climate and human health (Li et al, 2015), fine particles have been extensively studied in diverse fields (Aurela et al, 2015;Malaguti et al, 2015). Among them, the charging process of particles plays an essential part in many applications.…”