Real-time characterization of the mixing state and droplet growth kinetics of CCN sampled during ICARTT

Ground measurements of cloud condensation nuclei (CCN) were made during July and August of 2004 as part of the NEAQS ITCT-2K4 (New England Air Quality Study - Intercontinental Transport and Chemical Transformation 2004) mission at the Thompson Farm sampling site maintained by the University of New Hampshire. Over the duration of the field campaign, the two CCN instruments (built by Droplet Measurement Technologies, Inc.) were used to measure the concentration of CCN at 0.1, 0.2, 0.3, 0.37, 0.4, 0.5 and 0.6% supersaturation continuously over extended periods of time. One of the CCN instruments sampled unclassified ambient aerosol and the other was operated in our newly developed "Scanning Mobility CCN Analysis" technique (in which classified ambient aerosol obtained from a scanning DMA is introduced into the CCN counter), which allows the rapid characterization of the activation properties of classified ambient aerosol. Aerosol size distributions were measured using a TSI scanning mobility particle sizer (SMPS 3080). Finally, an Aerodyne Aerosol Mass Spectrometer (AMS) operated by the University of New Hampshire was used to measure the size-resolved chemical composition of the aerosol. We analyze the measurements using detailed numerical models of the CCN instrumentation. By close integration of measurements and theory, CCN closure can be assessed and real-time observations of CCN mixing state, ageing and droplet growth kinetics can be obtained. Finally, we derive characteristic aggregate properties for the carbonaceous component of the CCN, and discuss how this information can be introduced into aerosol-cloud interaction modules for GCM assessments of the aerosol indirect effect.