Regional aerosol properties: Comparisons of boundary layer measurements from ACE 1, ACE 2, Aerosols99, INDOEX, ACE Asia, TARFOX, and NEAQS

Means and variability of aerosol chemical composition and optical properties are compared for the first and second Aerosol Characterization Experiments (ACE 1 and ACE 2), a cruise across the Atlantic (Aerosols99), the Indian Ocean Experiment (INDOEX), the Asian Aerosol Characterization Experiment (ACE Asia), the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX), and the New England Air Quality Study (NEAQS). These experiments were focused either on the remote marine atmosphere (ACE 1) or areas downwind of continental aerosol source regions including western Europe, North America, Africa, India, and Asia. Presented here are size‐segregated concentrations of aerosol mass, sea salt, non‐sea‐salt (nss) SO 4 = , NH 4 + , NO 3 − , dust, organic carbon (OC), elemental carbon (EC), and nss K + , as well as mass ratios that are commonly used to identify aerosol sources and to assess aerosol processing (Cl − to Na + , OC to nss SO 4 = , EC to total carbon (TC), EC to nss SO 4 = , nss K + to EC, Fe to Al, and Si to Al). Optical properties that are compared include size‐segregated scattering, backscattering, and absorption coefficients, and single‐scattering albedo at 550 nm. Size‐segregated mass scattering and mass absorption efficiencies for the total aerosol and mass extinction efficiencies for the dominant chemical components also are compared. In addition, we present the contribution to light extinction by the dominant chemical components for each region. All data are based on shipboard measurements performed at a relative humidity of 55 ± 5%. Scattering coefficients and single‐scattering albedos also are reported at ambient relative humidity (RH) using published values of f(RH). Finally, aerosol optical depths from each region are compared. Identical sampling protocols were used in all experiments in order to eliminate sampling biases and to make the data directly comparable. Major findings include (1) nss SO 4 = makes up only 16 to 46% of the submicron aerosol mass, which means there is a large and variable fraction of the aerosol that is not sulfate, (2) particulate organic matter (POM) makes up 1 to 51% of the submicron mass, with highest POM mass fractions observed downwind of the NE United States, (3) highest submicron mass fractions of EC and lowest single‐scattering albedos were observed in biomass‐burning plumes from Africa and downwind of the Indian subcontinent, (4) NO 3 − was found predominantly in the supermicron size range due to the interaction of gas phase oxidized nitrogen species with sea salt aerosol, and (5) mass extinction efficiencies for the individual chemical components were consistent between regions. All data presented are available as auxiliary material.