Particle Number Size Distributions at an Urban Site in southern Sweden: Estimates of the Contribution of Urban Particle Sources Erik Swietlicki 1, Andreas Massling 1, Ingela Dahlberg 1, Jakob Löndahl 1, Adam Kristensson 2, Henric Nilsson 3, Susanna Gustafsson 3 and Matthias Ketzel 4 1 Division of Nuclear Physics, Lund University, Lund, Sweden 2 Department of Chemistry, Copenhagen University, Copenhagen, Denmark 3 Environment and Health Protection Board, City of Malmö, Malmö, Sweden 4 Department of Atmospheric Environment, National Environmental Research Institute, Roskilde, Denmark Research funded by the Swedish FORMAS Paper 8A1, Session 8, IAC 2006

Motivation – Human Health CAFE estimates that fine particles (PM2.5) and ozone combined are responsible for 370,000 premature deaths each year in EU25, and the loss of 3.6 millions years of life annually. (CAFE: Impact Assessment of the Thematic Strategy on Air Pollution and the Directive on “Ambient Air Quality and Cleaner Air for Europe”, SEC(2005)1133, Brussels, 21 Sept ( WHO estimates that exposure to fine particulate matter in outdoor air leads to about deaths (and years of life lost) annually in Europe. (WHO, World Health Report 2002, Geneva) For Sweden, Forsberg et al. (2005) estimated that the current population exposure to PM10 results in 5000 premature deaths annually. RIP (RIP = Respired Inhalable Particles … and died!)

Motivation – Climate Size-resolved emission data are often close to source (tunnels, tail-pipe, street canyons…). Regional/global scale models need the size distributions of the urban plume crossing over the city limits. Are aerosol dynamics (coagulation, condensation…) fast enough to significantly modify the urban plume aerosol size distribution?

Measurements sites – Southern Sweden Vavihill Malmö Court House Malmö 55 36' 23'' N, 13 0' 9'' E

Malmö SMPS system Own design, manufacture and calibration Medium-long DMA (Vienna-type, own manufacture) Particle counter: TSI CPC 3760A nm Closed-loop (driers and filters in loop) Scanning mode (up and downscan, Labview software) CPC desmearing to improve time resolution Time resolution: 3 min RH and T sensors for data QA Measurements started April 2005

Court House, Malmö, Sweden (Urban Roof-top Measurement Site) Gas phase: NO, NO 2, SO 2, CO PM2.5, PM10 Meteorological data, nearby mast Environment and Health Protection Board, City of Malmö, Sweden

The Vavihill site Regional background – Southern Sweden Twin-DMPS (3-900 nm)

Aerosol Size Distributions Urban Roof-top – Malmö, Sweden April 2005 – April 2006 Mean Percentiles Median 70% 90% 30% 10% cm -3

Statistics April 2005 – April 2006 Particle concentration MeanMedianMaxMin Number (cm -3 ) Surface (µm 2 /cm 3 ) Volume (µm 3 /cm 3 ) Aerosol Size Distributions Urban Roof-top – Malmö, Sweden Mean PM2.5  10 µg/m 3

National holidays have been omitted. Aerosol Size Distributions Urban Roof-top – Malmö, Sweden April 2005 – April 2006 Average Size Distributions  50 nm Weekdays

Average size distributions for the various wind sectors. Aerosol Size Distributions Urban Roof-top – Malmö, Sweden Harbour Malmö Harbour Malmö city

Court House, Malmö (urban roof-top measurement site) Sources to the urban aerosol (size distribution): Long-range transported regional background Urban sources (road traffic, ship traffic, industry,…) Heating: oil and wood combustion (minor sources in Malmö) + aerosol dynamics transforming the size distribution within the city limits (condensation, coagulation, deposition, dilution) Attempt to separate: Urban contribution to the urban roof-top concentrations (Urban measurements – Regional Background) Local traffic contribution (Highest 20% [NO]/[NO 2 ] ratios) Ship plumes (High [SO 2 ], wind direction from harbour area)

Estimated Traffic Contribution Malmö Urban Roof-top Method suggested by Janhäll et al. (2004) Local traffic contribution: Cases with highest 20% [NO]/[NO 2 ] ratios Urban background: Cases with lowest 20% [NO x ] subtracted Size-dependent emission factors derived from a Swedish tunnel study (Kristensson et al., 2004) are shown for comparison. Tunnel study Estimated Traffic

Derived Traffic Contribution Mode GMDs: 13 nm, 25 nm, 68 nm

Rådhuset Ship Traffic Contribution

Ship plumes from Malmö City Harbour SO 2 Ship Plumes Nucleation mode particles from homogeneous nucleation of H 2 SO 4 + H 2 0 ?

Urban Roof-top – Regional Background Vavihill – Malmö Urban site (Malmö) Backgrund (Vavihill)

Malmö City Contribution to the Urban Roof-top Aerosol Mode GMDs: 8 nm, nm, nm Fresh aerosol (traffic, ships,..) + processed within city limits Weekdays Weekends Malmö City Contribution Malmö City Contr.

Malmö City Contribution to the Urban Roof-top Aerosol Mode GMDs: 8 nm, nm, nm Fresh aerosol (traffic, ships,..) + processed within city limits Malmö City Contribution Weekdays July 2005 Malmö City Contribution Traffic Ship?

Harbour Inlet Mode 1 N1 (cm-3) CMD1 (nm) Sigma Mode 2 N2 (cm-3) CMD2 (nm) Sigma Mode 3 N3 (cm-3) CMD3 (nm) Sigma Mode 4 N4 (cm-3) CMD4 (nm) Sigma The urban contribution seems to be from road traffic plus ship movements in the harbour. Could the size shift from 25 nm to 40 nm be caused by aerosol dynamics instead?

Method Ketzel, M. and Berkowicz, R. (2005): Multi-plume aerosol dynamics and transport model for urban scale particle pollution. Atmospheric Environment 39, AERO3 Model (E. Vignati, JRC) Input Assumptions: The background size distribution at Vavihill (3-modal) The estimated traffic emission size distribution (4-modal) Average wind speed = 4 m/s Emission density for Malmö = 230 (pt/cm 3 ) m/s Modelling Urban Aerosol Dynamics Question: Can particles grow from 25 to 40 nm in the urban background?

Regional background, Urban Traffic Emissions and Dilution, No Aerosol Removal process Modelling Urban Aerosol Dynamics 0 h 1 h 3 h 5 h Emissions

Regional background, Urban Traffic Emissions and Dilution, No Aerosol Removal process Regional background, Traffic Emissions, Dilution, Coagulation, Deposition with u*=1.33 m/s, No condensation Modelling Urban Aerosol Dynamics 0 h 1 h 3 h 5 h

Regional background, Urban Traffic Emissions and Dilution, No Aerosol Removal process Regional background, Traffic Emissions, Dilution, Coagulation Deposition with u*=1.33 m/s, No condensation Regional background, Traffic Emissions, Dilution, Coagulation, Deposition Condensation, Growth rate=6 nm/h, Condensing vapour conc. = 1.85 x 10 8 molec cm -3 Modelling Urban Aerosol Dynamics 0 h 1 h 3 h 5 h

Regional background, emissions, dilution, coagulation, deposition, condensation Modelling Urban Aerosol Dynamics 0 h 1 h Regional background, urban traffic emissions and dilution only Aerosol dynamics alone can not grow the 25 nm traffic mode to 40 nm. This latter mode is probably caused by ship traffic. Aerosol dynamics is nevertheless likely to affect the urban size distribution even within the city limits of a medium-sized city. The urban plume contribution to the rural bakground is not simply a linear combination of regional background plus urban emissions and dilution.

Particle Number Size Distributions at an Urban Site in southern Sweden: Estimates of the Contribution of Urban Particle Sources Erik Swietlicki, Andreas Massling, Ingela Dahlberg, Jakob Löndahl, Adam Kristensson, Henric Nilsson, Susanna Gustafsson and Matthias Ketzel > Conclusions < The dominant sources to the urban roof-top aerosol size distribution were determined and were identified as Long-range transport Local road traffic Ship traffic Aerosol dynamics play a role

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