Aerosol observations at Chebogue Point during the 1993 North Atlantic Regional Experiment: Relationships among cloud condensation nuclei, size distribution, and chemistry

Abstract

Observations of aerosol chemistry and microphysics were made at Chebogue Point, Nova Scotia, from August 16 to September 8, 1993 as part of the North Atlantic Regional Experiment (NARE) intensive. Most of the aerosols were classified into two groups according to the geometric mean volume diameter (Dgv) of the particles which contributed the greatest volume (sub‐0.5 μm). The group‐1 aerosols, representing 33% of the data, are characterized by Dgv of 0.18–0.19 μm; the group‐2 aerosols, representing 50% of the data, are characterized by Dgv of 0.20–0.22 μm; and the remaining aerosols bear similarities to either groups 1 or 2 but lie outside the Dgv ranges. The differences between these aerosol groups are consistent with the addition of sulfate to the group‐2 aerosols via recent processing through cloud. Factors supporting this possibility include the presence of low marine stratus upwind of the site only on days when the group‐2 aerosol was observed, the higher Dgv for the group‐2 aerosols consistent with the observed size threshold for activation in these clouds, and the association of non‐sea‐salt SO4= (nssSO4=) with larger particle sizes for the group‐2 aerosols. In general, the masses of the most abundant inorganic and organic ions, nssSO4= and oxalate, were associated with the main volume of the sub‐0.5‐μm particles. Cloud condensation nucleus (CCN) concentrations active at 0.4% supersaturation (CCN0.4) were highly correlated with the concentrations of particles >0.01 μm and oxalate and moderately correlated with nssSO4=. Concentrations of CCN active at 0.06% supersaturation (CCN0.06) correlate very well with the concentrations of particles >0.19 μm diameter. In the case of the recently cloud‐processed aerosols, for which nssSO4= is more strongly associated with particles >0.19 μm, the CCN0.06 also correlate well with nssSO4=. CCN spectra computed using the measured size distributions and aerosol chemistry agree well with the measured CCN.

Closure between measured and modeled cloud condensation nuclei (CCN) using size-resolved aerosol compositions in downtown Toronto

“…The aerosol/CCN closure studies which have been successful in achieving closure (Liu et al, 1996;Cantrell et al, 2001;Roberts et al, 2002 have seen high levels of sulfate, generally larger than 50% by mass. Only the Roberts et al (2002) study saw significant organic mass fractions (approx.…”

“…Liu et al (1996) made ground based aerosol and CCN measurements at Chebogue Point, Nova Scotia, during the 1993 NARE campaign. Composition information was derived from filter samples and the particles were divided into soluble and insoluble fractions, of which the soluble was assumed to be ammonium sulfate.…”

The importance of aerosol mixing state and size-resolved composition on CCN concentration and the variation of the importance with atmospheric aging of aerosols

“…CCN concentration was found to be predicted with sufficient accuracy assuming simplified composition and an internal mixture in some studies (e.g. Liu et al, 1996;Cantrell et al, 2001;Roberts et al, 2002;VanReken et al, 2003, Rissler et al, 2004Conant et al, 2004;Gasparini et al, 2006;Ervens et al, 2007;Chang et al, 2007;Andreae and Rosenfeld 2008;Wang et al 2008, Gunthe et al, 2009Rose et al, 2008a;Shinozuka et al, 2009), whereas other studies suggest prediction of N CCN may require detailed chemical composition, mixing state, and/or the properties of organics being taken into consideration (e.g., Mircea et al, 2005;Broekhuizen et al, 2006;Mochida et al, 2006;Stroud et al, 2007;Cubison et al, 2008;Quinn et al, 2008). Medina et al (2007) find a ∼35% overprediction of N CCN for semi-urban air masses in New Hampshire even when size-resolved aerosol composition is employed, and attribute the overprediction to the assumption of an internal mixture.…”

Cold and transition season cloud condensation nuclei measurements in western Colorado

“…The majority of their error probably resulted from instrument bias but they also note the importance of the treatment of aerosol composition in CCN prediction. This was also pointed out in earlier work by Liu et al (1996) who combined aerosol composition measurements with CCN predictions and found that some chemical constituents were correlated with N ccn .…”