AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Re-evaluating the Contribution of Sulfuric Acid in Atmospheric Nanoparticle Growth
VILLE VAKKARI, Petri Tiitta, Kerneels Jaars, Philip Croteau, Johan Paul Beukes, Miroslav Josipovic, Veli-Matti Kerminen, Markku Kulmala, Andrew D. Venter, Pieter G. van Zyl, Douglas Worsnop, Lauri Laakso, Finnish Meteorological Institute, Helsinki, Finland
Abstract Number: 283 Working Group: Aerosol Chemistry
Abstract In atmospheric new particle formation the survival probability of a newly-formed 1-2 nm particle depends strongly on its growth rate and subsequently on the concentration of condensable vapors in the air. However, atmospheric chemistry responsible for the growth of newly-formed aerosol particles to climate-relevant sizes is still not very well known. We utilized one year of simultaneous measurements of aerosol particle size distributions and on-line PM1 chemical composition with an aerosol chemical speciation monitor (ACSM) at the Welgegund measurement station in South Africa to investigate the composition of the growth in regional scale new particle formation (NPF) events.
During the measurement period from September 2010 to August 2011 we could estimate the chemical composition of the growth for 88 NPF events. Not surprisingly, the growth was dominated by either sulfuric acid accompanied by ammonium or organic compounds depending on the air mass origin and size of the growing particles. The contribution of sulfuric acid was larger during the early phases of the growth, but in clean conditions organic compounds originating from either biogenic emissions or savannah fires dominated the growth from 1.5 nm up to climatically relevant sizes.
Finally, we compared the observed growth by sulfuric acid to the calculated growth by sulfuric acid from gas phase sulfuric acid concentration, which is a commonly-used method if no aerosol chemical composition measurements are available. In clean conditions these two methods agreed reasonably well, but in high sulfuric acid concentrations the gas phase sulfuric acid calculation underestimated the observed growth by sulfuric acid by up to a factor of ten.