Airborne measurements of atmospheric carbonaceous aerosols during ACE-Asia

[1] Airborne levels of carbonaceous aerosols were measured using the Twin Otter aircraft during the Aerosol Characterization Experiment (ACE)-Asia. Particles were collected using a newly developed honeycomb denuder sampler and organic carbon (OC), elemental carbon (EC), and carbonate (CC) carbon levels determined using a thermal-optical carbon analyzer. During some flights, atmospheric layers could be identified as marine boundary, pollution dominated, or mineral dust dominated. Angstrom exponent ((a) over circle) values, calculated based on data from an onboard three-wavelength nephelometer, were used to discern the nature of some individual layers. Values of (a) over circle for individual layers ranged from 0.2 to 2, corresponding to dust- and pollution-dominated layers, respectively. OC and EC concentrations below 3 km ranged from 0.58 to 29 mug C m(-3) and from 0.20 to 1.8 mug C m 3, respectively. In general, for a given type of atmospheric layer, higher levels of total carbon (TC) were observed during ACE-Asia than those observed during ACE-2, Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and Indian Ocean Experiment (INDOEX). Mixed layers of dust and pollution were found on some occasions. CC was detected in samples taken from layers in which (a) over circle = 1.6, indicating that significant amounts of dust can be present even though (a) over circle > 0.2. A linear regression of light absorption coefficient sigma(ap) (Mm(-1)) versus EC concentration had an r(2) of only 0.50, indicating that parameters other than the mass of EC significantly affected the value of sigma(ap). The mass absorption coefficient E-abs (m(2) g(-1)) varied by as much as a factor of 8 between sampling events, and the average value of 11 m(2) g(-1) (+/-5.0) agrees well with previous published values.