Aerosol particle chemical characteristics measured from aircraft in the lower troposphere during ACE-2

During the Aerosol Characterization Experiment (ACE-2), filter samples were collected aboard the Center For Interdisciplinary Remotely Piloted Aircraf t Studies (CIRPAS) Pelican aircraft near Tenerife in June and July of 1997. The flights included constant altitude measurements in the boundary layer as well as profiles up to 3800 m providing detailed chemical information ab out the composition of the aerosol distribution in the lower troposphere. T hree cases with different air mass origins - clean marine air, anthropogeni cally-influenced air from the European continent, and dust-laden air from t he Sahara - were identified. The samples were analyzed by ion chromatograph y (IC) for ionic species, by combined thermal and optical analysis (TOA) fo r organic carbon, and by total reflection X-ray fluorescence (TXRF) for ele mental composition. Particle composition and size distributions For the ran ge of air masses encountered illustrate links in the chemical and microphys ical characteristics of aerosol From different sources. Clean marine air ma sses were characterized by low particle number and mass concentrations with no detectable metals, while anthropogenically-influenced and dust-laden ai r had high number, mass, and trace metal concentrations. Anthropogenic sour ces were characterized by high concentrations of submicron particles and so me Fe and Cu, whereas dust particle loadings included a significant mass of micron-sized particles and significant loadings of Fe, in addition to smal l amounts of Mn, Cu, and Ni. These results showed similar tracers for air m ass origin as those found in other measurements of oceanic and continental air masses. Aerosol optical properties were estimated with a simplified mod el of the aerosol based on the measured compositions. The real and imaginar y refractive indices and single scattering albedos differed significantly a mong the three types of aerosol measured, with clean marine aerosol propert ies showing the least absorption and dust-containing aerosols showing the m ost. There were only small differences in optical properties for the two di fferent cases of clean marine aerosol, but some significant differences bet ween the two dust cases. Since measurement uncertainties affect these calcu lations, we studied the type of mixing and the fraction of absorbing specie s and found the calculation was sensitive to these variations only for the dust-containing aerosol case, probably due to the small amount of water pre sent. While the optical properties varied little with composition for clean marine and anthropogenically-influenced cases, they showed a strong depend ence on variations in particle composition and mixing state for the dust-co ntaining cases.