Peter Tunved, Johan Ström, Radovan Krejci Department of Applied Environmental Science, Stockholm University CLIMSLIP meeting

+10 years DMPS size distributions +9 years Particle Soot Absorption Photometer (PSAP) +10 years nephelometer data ~3 years of weekly OC/EC samples CO 2, CN>10nm (CPC3010) and CN>3nm (CPC3025)

Tunved et al., MS 2011 The seasonal distribution of aerosol number concentration is bimodal

Tunved et al., MS 2011

LRT dominates the aerosol number during the dark half of the Arctic year...but local production gets increasingly important during the summer months Which processes control this seasonal behaviour? Prime suspects: seasonality of source areas, photochemistry and removal processes

Depletion of mass ”Recovery” What is the role of sources and what is the role of sinks? HAZE Tunved et al., MS 2011

Tunved et al., MS in preparation

trajectory transport cases associated with observation of mass Tunved et al., MS in preparation

WHOLE YEAR

Dark period Sunlit period Tunved et al., MS in preparation

Prec=2mm Prec=4mm Prec=6mm Prec=8mm Prec=14mm Prec=18mm Prec=28-32mm Prec=38-42mm

Precipitation results in removal of particles in all size classes during the dark period of the year......while precipitation initially remove number and mass during sunlit period, but particle number seem to be regenerated when precipitation gets even higher

Sunlit conditions  photochemical production of nucleating species Photochemical production+low condensation sink  new particle formation Aitken mode typically less efficient CCN’s  establishment of a new aitken mode that in fact is larger than without any precipitation at all i.e. a second generation of particles is introduced whose chemical properties likely is different from original population

Study the relation between soot and precipitation Soot is clearly removed by precipitation during both sunlit and dark season Tunved et al., MS in preparation

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Soot is likely to be less effectively scavenged compared to more soluble species  potentially enrichment of soot after consequtive precipitation events during the dark period......but summer time shows the opposite: the soot fraction is reduced with increasing precipitation: this means that new mass is added from sources different than the original ones

Soot and re-generated Aitken mode have different sources: Secondary production!! Tunved et al., MS in preparation

No rain cases Rainy cases

Arctic aerosol exhibit a very pronounced seasonality with respect to number and mass concentration This seasonality seem to correlate well with dominating sink processes as represented by precipitation during transport – During dark period wet removal result in depletion of mass, number and soot content of aerosol – During sunlit period wet removal results in an initial removal of particle mass and number. This initial decrease is however followed by a relative increase of particle number and mass, a feature not shared by the aerosol soot content, which instead is depleted

Thus, during photochemically active conditions, wet removal facilitates regeneration of particle number and mass and establishement of a an aerosol population significantly different from the old one This is most likely the result of reduced CS, favouring nucleation and growth

Use exisiting data to develope a sink parameterisation for soot using precipitation data Extend the current analysis with modelling to resolve the role of the combined effect from annual variation in source strength and wet removal