Primary versus secondary contributions to particle number concentrations in the European boundary layer
Creators: name: Reddington, Carly L.
name: Carslaw, Ken S.
name: Spracklen, Dominick V.
name: Frontoso, Maria Grazia
name: Collins, Lisa M.
name: Merikanto, Joonas
name: Minikin, Andreas
name: Hamburger, Thomas
name: Coe, Hugh
name: Kulmala, Markku
name: Aalto, Pasi Pekka
name: Flentje, Harald
name: Plass-Dülmer, Christian
name: Birmili, Wolfram
name: Wiedensohler, Alfred
name: Wehner, Birgit
name: Tuch, Thomas
name: Sonntag, Alfred
name: O'Dowd, Collin D.
name: Jennings, Stephen G.
name: Dupuy, Regis
name: Baltensperger, Urs
name: Weingartner, Ernest
name: Hansson, Hans-Christen
name: Tunved, Peter
name: Laj, Paolo
name: Sellegri, Karine
name: Boulon, Julien
name: Putaud, Jean-Philippe
name: Gruening, Carsten
name: Swietlicki, Erik
name: Roldin, Pontus
name: Henzing, J.S.
name: Moerman, Marcel
name: Mihalopoulos, Nikolaos
name: Kouvarakis, Giorgos
name: Ždímal, Vladimir
name: Zíková, Nadezda
name: Marinoni, Angela
name: Bonasoni, Paolo
name: Duchi, Rocco
Publisher: name: Copernicus
Year: 2011
Subjects: subject: 550 - Geowissenschaften

description: It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter &gt;50 nm (N50) and &gt;100 nm (N100) were well captured by the model (R2≥0.8) and the normalised mean bias (NMB) was also small (−18% for N50 and −1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2≥0.8, NMB = −52% and −29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.