The 2nd Aerosol Characterization Experiment (ACE-2): general overview and main results

Abstract

This overview summarizes the objectives of the Aerosol Characterization Experiments (ACEs) of the International Global Atmospheric Chemistry (IGAC) project and the research strategy implemented in the second of this series of experiments (ACE-2). ACE-2 took place from 16 June to 24 July 1997, over the sub-tropical North-East Atlantic. It provided an opportunity to study the properties, processes and effects of contrasting aerosol types in this region, including background marine and anthropogenic pollution aerosol in the marine boundary layer (MBL), and background aerosol and mineral dust in the overlaying free troposphere (FT). The major achievements of ACE-2 include: (a) identification of entrainment, in-cloud scavenging and coagulation as the major processes transforming a pollution aerosol transported within the MBL; (b) the first documentation of the indirect radiative effect of aerosols at the scale of a cloud ensemble in continental pollution outflow; (c) observation of a wide range in the contribution of organic material to the sub-micron aerosol mass, with possibly the highest contribution in the free tropospheric; (d) improved understanding of the role of condensing HCl, HNO 3 and NH 3 as a growth mechanism of sub-micron aerosols in polluted air masses advecting over the ocean. A close connection was observed between meteorological factors (such as horizontal and vertical wind speed, boundary layer development, entrainment, humidity fields) and aerosol and cloud characteristics. In the ACE-2 region, these meteorological factors, rather than aerosol microphysics and chemistry, often dominated the shaping of the aerosol size distribution and/or their effect on radiation and clouds. The ACE-2 data presently analyzed provide a qualitative, and in many cases a quantitative understanding of the complex gas/aerosol/cloud system in the sub-tropical marine environment. This will guide future model development. Some major data sets are still to be analyzed.

Empirical relationships between aerosol mass concentrations and Ångström parameter

“…A literature search for t A data in combination with simultaneous measurements of aerosol composition led to the ACE-2 experiment conducted over the Atlantic Ocean in July 1997 (cf. Raes et al [2000]). BC and Na data, collected at the Izaña observatory (28.30°N, 16.50°W) were published by Putaud et al [2000].…”

“…The results are tested versus an independent data set obtained at the Baltic in July 1997. Additional tests were made using data obtained over the Atlantic Ocean during ACE-2 (e.g., Raes et al [2000]) and from Quinn et al [2001].…”

Characterization and parameterization of atmospheric particle number‐, mass‐, and chemical‐size distributions in central Europe during LACE 98 and MINT

“…Aerosol characterization experiments are essential to describe the atmospheric aerosol for different polluted regions in the world as a matter of defining the state of the atmosphere and providing model input. Several international field measurements such as the First Aerosol Characterization Experiment (ACE 1) [ Bates et al , 1998] and the Second Aerosol Characterization Experiment (ACE 2) [ Raes et al , 2000] were performed to characterize the clean marine aerosol in the South Pacific, and European aerosol outflow over the North Atlantic, respectively. Emphasis was put on intensive ground and airborne measurements.…”

Aerosol optical properties from columnar data during the second Aerosol Characterization Experiment on the south coast of Portugal

“…[3] Multiplatform experiments such as the second Aerosol Characterization Experiment CLEARCOLUMN (ACE-2 CLEARCOLUMN) [Russell and Heintzenberg 2000;Raes et al, 2000] are an ideal opportunity to validate both the aerosol physical models as well as the aerosol optical properties, by comparing different radiative, optical, and physico-chemical measurements. Examples are given by Schmid et al [2000] and Collins et al [2000].…”