10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Influence of Traffic Emissions on Chemical Composition of Particles in Helsinki, Finland
MINNA AURELA, Kimmo Teinilä, Sanna Saarikoski, Jarkko Niemi, Harri Portin, Pasi Aalto, Liisa Pirjola, Hilkka Timonen, Finnish Meteorological Institute
Abstract Number: 1248 Working Group: Source Apportionment
Abstract Particle emissions from traffic are known to significantly contribute to regional air quality and the Earth’s radiation budget. Particulate matter (PM) emission categories for traffic has been estimated to be 27% in the Helsinki metropolitan area in Finland. Primary particles emitted from motor vehicles consist mainly black carbon and organic material, but motor vehicle emissions include also gaseous compounds like volatile organic compounds, which may produce secondary particles. In order to reduce PM concentrations and improve urban air quality, detailed information on PM concentrations, chemical composition and the contribution of local sources to PM is needed.
The concentration and chemical composition of submicron PM were measured in Helsinki from August 2016 to May 2017 simultaneously at two urban locations: at the urban background site (SMEAR III) and at the curbside in a street canyon (Supersite). The SMEAR III, is located on a small hill, approximately 150m away from one of the main streets (43 000 vehicles/working day) leading to city center. The other station, Supersite, is located in a street canyon on the sidewalk next to another main street (28 000 vehicles/working day) leading to the city center. The chemical composition of non-refractory submicron particles (NRPM1: organic aerosol (OA), sulfate, nitrate, ammonium and chloride) was measured in-real time with an aerosol chemical speciation monitor (ACSM). An aethalometer or a multi-angle absorption spectrometer were used for black carbon measurements. In addition, particles number size distributions and concentrations of trace gases were measured. The mass to charge ratio (m/z) of 55 and 57 and their ratio to total OA, f55 and f57, respectively, were used for estimating the contribution of traffic related aerosol. These m/z’s are mainly hydrocarbon ion fragments (C4H7+ and C4H9+) and are typically seen in a mass spectra of vehicle exhaust. Additionally, the multi-linear engine (ME-2) are used for source apportionment of OA.
At both sites, NRPM1 was dominated by organic aerosol. At the urban background site, traffic-related OA had larger contribution to total OA in wintertime as highest f55 and f57 values were detected on December and lowest during warmer months (Aug-Sep, 2016 and April-May, 2017). At the street canyon site, no clear seasonal patterns were observed, although the highest values of f55 and f57 were observed on December. Regarding the diurnal variation, f57 had more pronounced diurnal variation at the curbside than at the urban background while f55 was similar during the day at both sites without any clear diurnal variation.
This study has been funded by TEKES funded INKA-ILMA/EAKR project (Tekes nro: 4588/31/2015) and by the Regional innovations and experimentations funds AIKO, governed by the Helsinki Regional Council (project HAQT, AIKO014).