The NASA Global Tropospheric Experiment (GTE) Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) expedition was conducted September 21 through October 26, 1992, to investigate factors responsible for creating the seasonal South Atlantic tropospheric ozone maximum. During these flights, fine aerosol (0.1–3.0 μm) number densities were observed to be enhanced roughly tenfold over remote regions of the tropical South Atlantic and greater over adjacent continental areas, relative to northern hemisphere observations and to measurements recorded in the same area during the wet season. Chemical and meteorological analyses as well as visual observations indicate that the primary source of these enhancements was biomass burning occurring within grassland regions of north central Brazil and southeastern Africa. These fires exhibited fine aerosol (N) emission ratios relative to CO (dN/dCO) of 22.5 ± 9.7 and 23.6 ± 15.1 cm−3 parts per billion by volume (ppbv)−1 over Brazil and Africa, respectively. Convection coupled with counterclockwise flow around the South Atlantic subtropical anticyclone subsequently distributed these aerosols throughout the remote South Atlantic troposphere. We calculate that dilute smoke from biomass burning produced an average tenfold enhancement in optical depth over the continental regions as well as a 50% increase in this parameter over the middle South Atlantic Ocean; these changes correspond to an estimated net cooling of up to 25 W m−2 and 2.4 W m−2 during clear‐sky conditions over savannas and ocean respectively. Over the ocean our analyses suggest that modification of CCN concentrations within the persistent eastern Atlantic marine stratocumulus clouds by entrainment of subsiding haze layers could significantly increase cloud albedo resulting in an additional surface radiative cooling potentially greater in magnitude than that caused by direct extinction of solar radiation by the aerosol particles themselves.

We report airborne measurements of total and nonvolatile (at T < 290°C) fine and ultrafine aerosol emission indices (EI's) generated by a variety of jet aircraft. The data were obtained using an instrumented jet aircraft, flown repeatedly through aircraft wakes. These aircraft were observed to produce 0.5hyphen;10 × 1015 nonvolatile particles kg−1 of fuel burned. Their numbers varied as a function of aircraft type, age, and engine operating parameters, but less with atmospheric conditions. Large numbers of volatile aerosols were measured in all cases. Volatile EI's ranged from 0.1 to 40×1016 kg−1 fuel burned. The observed soot emissions are estimated to have only a minor impact on atmospheric aerosol loading, but a future fleet producing such high concentrations of implied sulfate aerosols could perturb cloud formation and heterogeneous chemical processes in the upper troposphere/lower stratosphere.

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[1] Intercomparisons of chemical, aerosol, and meteorological measurement systems were conducted in the spring of 2001 between the NASA Wallops P3-B and the NCAR EC-130Q aircraft during overlapping portions of the concurrent tropospheric missions: the Global Tropospheric Experiment's (GTE) Transport and Chemical Evolution in the Pacific (TRACE-P) and Aerosol Characterization Experiment's ACE-ASIA mission, respectively. Both aircraft were equipped with similar air-motion measurement systems and in situ meteorology sensors designed to measure the eddy-correlation fluxes of momentum, heat, and water vapor. This paper presents the results of the informal intercomparison flight legs at two altitudes within the marine boundary layer performed over the Sea of Japan. The variances and spectra of the three-dimensional winds and temperature are presented along with the cospectra of the vertical velocities and various parameters. The results show good agreement between the measurements obtained from the two aircraft. Discrepancies in the data are analyzed and discussed.

NASA's Arctic Boundary Layer Expedition (ABLE 3A) conducted during the summer of 1988 focused on the distribution of trace species in the Alaskan Arctic troposphere (altitudes <7 km) and the relative importance of surface sources/sinks, local emissions, distant transport, and tropospheric/stratospheric exchange. In situ ozone and aerosol number density and size data obtained during aircraft flights from Point Barrow and Bethel, Alaska, are discussed. Data are also presented for the ferry flights between Wallops Island, Virginia, and Point Barrow, Alaska, via Thule, Greenland. The major source of summer ozone for the troposphere is the intrusion of stratospheric air and subsequent transport to the lower altitudes. Photochemistry of mixed layer emissions and ozone transported from high northern latitude urban/industrialized areas do not appear to play major roles as sources of ozone for the Alaska region. Ozone gradients reflect the loss at the surface and supply from the stratosphere. Free‐tropospheric ozone (3‐ to 7‐km altitude) averaged 74 ppbv compared to 32 ppbv for the mixed layer. All four mixed layers studied (water, wet tundra, dry tundra, and boreal forest) are net ozone sinks. Ozone loss mechanisms are a combination of the destruction via photochemistry, chemical reactions with surface emissions, and direct loss through deposition to the surface. The boreal forest is the most efficient of the ozone sinks. Aerosol data showed that, of the mixed layers studied, the boreal forest has the largest increase in aerosol number density relative to the free troposphere. With the exception of the boreal forest, a significant portion of mixed layer aerosols are from the free troposphere. Results also show that while, in theory, free‐tropospheric air can be classified as originating from continental or maritime regions (Siberia, Canada, Pacific Ocean, Gulf of Alaska), little difference was found in the ozone and fine aerosol number density composition of the air. This is attributed, in part, to modification of the air during transport from its source region.