AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Mass-Mobility Measurements of Urban and Background Aerosol – Measured with a DMA-TD-APM System
ERIK, Z NORDIN, Jenny Rissler, Axel C. Eriksson, Emilie Hermansson, Adam Kristensson, Erik Swietlicki, Joakim Pagels, Lund University, Sweden
Abstract Number: 54 Working Group: Urban Aerosols
Abstract Soot particles emitted in urban environments are transformed to spherical-like particles through atmospheric aging during long range transport, this alters the climate and health affecting properties of the particles. The timescale of the aging and the composition of the aged aerosol are important parameters that need more investigation. For this purpose, mass-mobility measurements, using a Differential Mobility Analyzer-Aerosol Particle Mass analyzer (DMA-APM) system, were performed in consecutive winters in the city of Copenhagen, Denmark and at the rural background station Vavihill, 60 km northeast of Copenhagen.
A thermo denuder (TD, heated to 300 °C, residence time ~10 s) between the DMA and APM was used in selected experiments. Parallel measurements included a SMPS and a Soot-Particle-AMS were also performed. From the mass mobility relationship the effective density of the aerosol could be determined.
DMA-TD-APM measurements at Vavihill showed a dominant mode with almost size independent effective density mode at 1.3 - 1.4 g cm$^(-3), independent of wind direction, interpreted as long range transported aerosol particles. A size dependent mode at lower effective densities were detected for some measurement days predominantly at southern wind directions interpreted as freshly emitted or lightly aged soot.
The mode of fresh soot particles was essentially non-volatile in terms of mass when sampled through the thermo denuder. Most long range transported particles proved to have high volatile mass fractions in the thermo denuder experiments, there was a broad signal corresponding to very low masses, significantly lower than the soot mode. From this we conclude that the long range transport aerosol mainly consists of rather volatile material and that only a minor fraction of the mass can be interpreted as soot.
This work was financed by the Swedish research council FORMAS.