Articles | Volume 17, issue 2
Research article
24 Jan 2017
Research article |  | 24 Jan 2017

Size-resolved aerosol and cloud condensation nuclei (CCN) properties in the remote marine South China Sea – Part 1: Observations and source classification

Samuel A. Atwood, Jeffrey S. Reid, Sonia M. Kreidenweis, Donald R. Blake, Haflidi H. Jonsson, Nofel D. Lagrosas, Peng Xian, Elizabeth A. Reid, Walter R. Sessions, and James B. Simpas

Abstract. Ship-based measurements of aerosol and cloud condensation nuclei (CCN) properties are presented for 2 weeks of observations in remote marine regions of the South China Sea/East Sea during the southwestern monsoon (SWM) season. Smoke from extensive biomass burning throughout the Maritime Continent advected into this region during the SWM, where it was mixed with anthropogenic continental pollution and emissions from heavy shipping activities. Eight aerosol types were identified using a k-means cluster analysis with data from a size-resolved CCN characterization system. Interpretation of the clusters was supplemented by additional onboard aerosol and meteorological measurements, satellite, and model products for the region. A typical bimodal marine boundary layer background aerosol population was identified and observed mixing with accumulation mode aerosol from other sources, primarily smoke from fires in Borneo and Sumatra. Hygroscopicity was assessed using the κ parameter and was found to average 0.40 for samples dominated by aged accumulation mode smoke; 0.65 for accumulation mode marine aerosol; 0.60 in an anthropogenic aerosol plume; and 0.22 during a short period that was characterized by elevated levels of volatile organic compounds not associated with biomass burning impacts. As a special subset of the background marine aerosol, clean air masses substantially scrubbed of particles were observed following heavy precipitation or the passage of squall lines, with changes in observed aerosol properties occurring on the order of minutes. Average CN number concentrations, size distributions, and κ values are reported for each population type, along with CCN number concentrations for particles that activated at supersaturations between 0.14 and 0.85 %.

Short summary
Aerosol particles were measured by ship in remote marine regions of the South China Sea as part of the 2012 7 Southeast Asian Studies (7SEAS) experiments. As the particle populations changed throughout the experiment, the distribution of particle sizes and the amount of water that collected on them changed as well. These changes were associated with various impacts from smoke, sea salt, and pollution sources, and impact how clouds form and precipitation occurs in the region.
Final-revised paper