Primary versus secondary contributions to particle number concentrations in the European boundary layer

Abstract

Abstract.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 nucleiCorrespondence to: C. L. Reddington (c.reddington@see.leeds.ac.uk) (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 Published by Copernicus Publications on behalf of the European Geosciences Union. C. L. Reddington et al.: Primary vs. secondary contributions to PN concentrationscampaign-mean number concentrations of particles with diameter >50 nm (N 50 ) and >100 nm (N 100 ) were well captured by the model (R 2 ≥0.8) and the normalised mean bias (NMB) was also small (−18 % for N 50 and −1 % for N 100 ). 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 (R 2 ≥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.

The direct and indirect radiative effects of biogenic secondary organic aerosol

“…The global annual production of SOA from these yield experiments is detailed in Table 2 and all lie within the wide range of previous estimates (Griffin et al, 1999;Kanakidou et al, 2005;Goldstein and Galbally, 2007;Heald et al, 2010Heald et al, , 2011Spracklen et al, 2011b). In GLOMAP, the simulated aerosol size distributions, and therefore the CCN concentrations, are sensitive to the treatment of primary anthropogenic emissions (Reddington et al, 2011;Spracklen et al, 2011a), in particular the emission characteristics of primary carbonaceous aerosol. Here, we emit primary carbonaceous particles with the distribution characteristics described by Stier et al (2005) in our standard simulations, i.e.…”

“…The treatment of primary carbonaceous emissions has been shown to strongly influence particle number concentrations and aerosol size distributions simulated by global aerosol microphysics models (Reddington et al, 2011;Spracklen et al, 2011a). We therefore compared against measurements filtered to minimise the influence of these particles: that is, data for terrestrial locations with a simulated present-day / pre-industrial CCN concentration ratio (calculated from [CCN] expt.…”

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

“…The overall kappa-variability will be inferred and discussed in context with the effective average kappa of 0.3 ± 0.1 and 0.7 ± 0.2 as estimated by Andreae and Rosenfeld (2008) for the continental and marine background aerosol, respectively. The former value has recently been superseded by 0.3 ± 0.2 which seems still fairly well constrained with regard to cloud droplet formation (Reutter et al, 2009;Pawlowska, 2010, 2011). Kappa deduced from the CCN data (i.e.…”

“…GLOMAP predictions of particle number over Europe were compared to aircraft and ground-based measurements recorded during the May 2008 EUCAARI intensive campaign and Long Range Experiment (LONGREX) by Reddington et al (2011). It was found that the spatial distributions of campaign-mean number concentrations >50 nm (N 50 ) and >100 nm (N 100 ) dry diameter were well captured by the model (R 2 >0.8) and the normalised mean bias was also small (−18 % for N 50 and 1 % for N 100 ) if a small emission size was assumed for primary carbonaceous particles, as used by AEROCOM .…”

Aged boreal biomass-burning aerosol size distributions from BORTAS 2011

“…Adding to the database of observations helps constrain the uncertainties associated with aerosol size. Thus, to improve BB-aerosol-climate interactions in models, there is a need to characterize the size of particles in aging and aged biomass-burning plumes for a range of fire types and atmospheric conditions (Bauer et al, 2010;Chen et al, 2010;Lee et al, 2013;Pierce et al, 2007;Reddington et al, 2011;Spracklen et al, 2011). In this paper, we specifically investigate the size distributions measured in aged plumes (1-2 days) of large boreal forest fires over Canada.…”