Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 1: Size-resolved measurements and implications for the modeling of aerosol particle hygroscopicity and CCN activity

Abstract

Abstract. Atmospheric aerosol particles serving as Cloud Condensation Nuclei (CCN) are key elements of the hydrological cycle and climate. We measured and characterized CCN in polluted air and biomass burning smoke during the PRIDE-PRD2006 campaign from 1-30 July 2006 at a rural site ∼60 km northwest of the mega-city Guangzhou in southeastern China.CCN efficiency spectra (activated fraction vs. dry particle diameter; 20-290 nm) were recorded at water vapor supersaturations (S) in the range of 0.068% to 1.27%. The corresponding effective hygroscopicity parameters describing the influence of particle composition on CCN activity were in the range of κ≈0.1-0.5. The campaign average value of κ=0.3 equals the average value of κ for other continental locations. During a strong local biomass burning event, the average value of κ dropped to 0.2, which can be considered as characteristic for freshly emitted smoke from the burning of agricultural waste. At low S (≤0.27%), the maximum activated fraction remained generally well below one, indicating substantial portions of externally mixed CCN-inactive particles with much lower hygroscopicity -most likely soot particles (up to ∼60% at ∼250 nm).The mean CCN number concentrations (N CCN,S ) ranged from 1000 cm −3 at S=0.068% to 16 000 cm −3 at S=1.27%, which is about two orders of magnitude higher than in Correspondence to: D. Rose (d.rose@mpic.de) pristine air. Nevertheless, the ratios between CCN concentration and total aerosol particle concentration (integral CCN efficiencies) were similar to the ratios observed in pristine continental air (∼6% to ∼85% at S=0.068% to 1.27%). Based on the measurement data, we have tested different model approaches for the approximation/prediction of N CCN,S . Depending on S and on the model approach, the relative deviations between observed and predicted N CCN,S ranged from a few percent to several hundred percent. The largest deviations occurred at low S with a simple power law. With a Köhler model using variable κ values obtained from individual CCN efficiency spectra, the relative deviations were on average less than ∼10% and hardly exceeded 20%, confirming the applicability of the κ-Köhler model approach for efficient description of the CCN activity of atmospheric aerosols. Note, however, that different types of κ-parameters must be distinguished for external mixtures of CCN-active and -inactive aerosol particles (κ a , κ t , κ cut ). Using a constant average hygroscopicity parameter (κ=0.3) and variable size distributions as measured, the deviations between observed and predicted CCN concentrations were on average less than 20%. In contrast, model calculations using variable hygroscopicity parameters as measured and constant size distributions led to much higher deviations: ∼70% for the campaign average size distribution, ∼80% for a generic rural size distribution, and ∼140% for a generic urban size distribution. These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the Publ...

Mixing state of biomass burning particles by single particle aerosol mass spectrometer in the urban area of PRD, China

“…Studies have showed that internally mixed ECesulfate and OC-coated EC particles enhanced atmospheric absorption ability by increasing a particle's absorption efficiency by about 3 times compared to uncoated EC (Jacobson, 2001;Bond et al, 2006), and their ability as CCN by hydrophobic to hydrophilic surface alteration (Rose et al, 2010). Presented here are the first in situ chemically resolved measurements of the mixing state of biomass burning particles in the PRD Fig.…”

Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events

“…Nevertheless, particle number and size are expected to remain the major predictors for the variability of CCN concentration [Dusek et al, 2006;Rose et al, 2008b;Gunthe et al, 2009]. Reduced hygroscopicity of newly formed particles can be expected where SOA plays a major role in particle growth, e.g., over boreal and tropical forests [Tunved et al, 2006;Gunthe et al, 2009].…”

“…The $10% higher value of k inorg obtained in this study can be attributed to the higher proportion of ammonium nitrate. For the prediction of CCN concentrations and the modeling of cloud droplet formation, however, such small differences in k are likely negligible [Rose et al, 2008b;Gunthe et al, 2009;Reutter et al, 2009].…”

Assessment of cloud supersaturation by size-resolved aerosol particle and cloud condensation nuclei (CCN) measurements

“…The measurement data of the CCN efficiency spectra were corrected for differences in the CCNC and CPC counting efficiencies as described in Rose et al (2010), using a constant correction factor of 1.03. Moreover, a correction for multiply charged particles was performed according to .…”

“…As a result of long-term efforts and recent advances in atmospheric research, the CCN activity of atmospheric aerosol particles can be fairly well constrained by measurements and models (e.g., Kreidenweis, 2007, 2008;Gunthe et al, 2009;Kinne, 2009;Moore and Nenes, 2009;Juranyi et al, 2010;Pringle et al, 2010;Rose et al, 2010;Wex et al, 2010;Gunthe et al, 2011;Kim et al, 2011;Kulmala et al, 2011;Rose et al, 2011;Spracklen et al, 2011;Anttila et al, 2012;Christensen and Petters, 2012;Engelhart et al, 2012;Padró et al, 2012;Jurányi et al, 2013;Lance et al, 2013;Mikhailov et al, 2013;Petters and Kreidenweis, 2013). To fully describe the process of CCN activation and cloud droplet growth in the atmosphere, however, the supersaturation of water vapor in the cloud also needs to be known (e.g., Reutter et al, 2009;Pruppacher and Klett, 2010;Rosenfeld et al, 2012;Renno et al, 2013).…”