Stuart J. Piketh

Variability of biomass burning aerosol optical characteristics in southern Africa during the SAFARI 2000 dry season campaign and a comparison of single scattering albedo estimates from radiometric measurements

A priority network utilizing a common bus coupled to a plurality of priority seeking peripheral devices wherein a processor or any number of processors is connected to the common bus. Each successive peripheral device is connected to the common bus in increasing priority order, such that each device will have a unique priority defined. Each peripheral device is provided with an associated peripheral control unit. Each of the peripheral control units is connected in serial fashion on an enabling line with the output of the higher priority control unit providing an enabling input to the next lowest priority peripheral control unit, such that the highest priority device requesting bus access prevents all lower priority devices from gaining access to the common bus until the higher priority device has completed its data transfer.

Maritime Aerosol Network as a component of Aerosol Robotic Network

The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island-based AERONET measurements) at 500 nm is similar to 0.11 and Angstrom parameter (computed within spectral range 440-870 nm) is calculated to be similar to 0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship-based aerosol optical depth compares well to simultaneous island and near-coastal AERONET site AOD.

Lower tropospheric aerosol loadings over South Africa: The relative contribution of aeolian dust, industrial emissions, and biomass burning

The southern African haze layer is a ubiquitous subcontinental-scale feature of the lower atmosphere that extends to a depth of ∼5 km(∼500 hPa level) on non rain days, particularly in winter. Aerosols derived from biomass burning are commonly thought to contribute substantially to the total background aerosol loading within the layer. It is shown that in both summer and winter this supposition is without foundation over South Africa. Summer and winter aerosol loadings are derived from gravimetric analysis of stacked filter units and from proton-induced X ray emission (PIXE) analysis of one to four hourly resolved streaker samples. From concentrations of eleven inorganic elements, apportionment into four primary sources, biomass burning particulates, aeolian dust, industrial sulphur aerosols, and marine aerosols, has been effected. It is shown that the background biomass burning component of the total aerosol loading over South Africa in general, and within the plume of material being recirculated over South Africa and from there exported from the subcontinent south of 22°S to the Indian Ocean in particular, is minimal in both summer and winter. Except over coastal and adjacent inland areas, marine aerosols likewise make up a small fraction of the total loading. This is particularly so over the inland plateau areas. Crustally-derived aeolian dust and industrially-produced sulphur aerosols are demonstrated to be the major summer and winter constituents of the haze layer over South Africa and the particulate material being transported to the Indian Ocean region. Sulphur is transported within the aerosol plume exiting southern Africa to the Indian Ocean as agglomerates on aeolian dust nuclei.

Concentrations, distributions and critical level exceedance assessment of SO2, NO2 and O3 in South Africa

South Africa has been identified as a source of industrial pollution that is significant at a global scale. This study was designed to provide quantitative information, by direct measurement, across northeastern South Africa, which includes the highly industrialised Mpumalanga Highveld. The specific aim of the study was to evaluate whether or not acidic atmospheric pollution poses a threat to soils, plants and water bodies of South Africa. To address this aim, a network of 37 passive sampling sites was established to measure monthly mean concentrations of near-surface SO2, NO2 and ozone. The area covered extended over the northern and eastern interior of South Africa while avoiding sources of local emissions such as towns, mines and highways. The field campaign was conducted between August 2005 and September 2007. Spatial distributions and temporal trends for these pollutant gases were assessed. Critical levels analysis comparisons were made against applicable air quality standards, guidelines and limits to evaluate the potential for adverse atmospheric pollution impacts on regional environments. The assessment indicates that only in the central source area of the South African industrial Highveld are some levels exceeded. In remote areas, including the sensitive forested regions of the Drakensberg escarpment, pollutant concentrations are below the critical thresholds for environmental damage.

Haze layer characterization and associated meteorological controls along the eastern coastal region of southern Africa

[1] Episodes of regionally extensive haze were observed over southern African during the dry season intensive of the Southern African Regional Science Initiative (SAFARI 2000). Several case studies of southern African haze layers were examined and characterized in terms of physical structure as they exited off of the eastern coastal region of southern Africa. In situ observations of aerosols and trace gases and their physical and chemical characteristics were collected on board South African Weather Service Aerocommander research aircraft. Haze structure, based on these measurements, is examined as it varies with synoptic type. Despite strong differences in the observed ENSO regime between SAFARI 2000 and that observed during the Southern African Fire-Atmosphere Research Initiative (SAFARI-92) and their respective aerosol accumulation mechanisms (col Rrgions/weak anticyclones versus strong anticyclones), a surprising degree of consistency in the observed vertical structure of the lower troposphere was found in southern Africa. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: haze layers, synoptic circulations, ENSO

Direct observation of two dimensional trace gas distributions with an airborne Imaging DOAS instrument

In many investigations of tropospheric chemistry information about the two dimensional distribution of trace gases on a small scale (e.g. tens to hundreds of metres) is highly desirable. An airborne instrument based on imaging Differential Optical Absorption Spectroscopy has been built to map the two dimensional distribution of a series of relevant trace gases including NO 2, HCHO, C2H2O2, H2O, O4, SO2, and BrO on a scale of 100 m. Here we report on the first tests of the novel aircraft instrument over the industrialised South African Highveld, where large variations in NO2 column densities in the immediate vicinity of several sources e.g. power plants or steel works, were measured. The observed patterns in the trace gas distribution are interpreted with respect to flux estimates, and it is seen that the fine resolution of the measurements allows separate sources in close proximity to one another to be distinguished.

A seasonal air transport climatology for Kenya

A climatology of air transport to and from Kenya has been developed using kinematic trajectory modeling. Significant months for trajectory analysis have been determined from a classification of synoptic circulation fields. Five-point back and forward trajectory clusters to and from Kenya reveal that the transport corridors to Kenya are clearly bounded and well defined. Air reaching the country originates mainly from the Saharan region and northwestern Indian Ocean of the Arabian Sea in the Northern Hemisphere and from the Madagascan region of the Indian Ocean in the Southern Hemisphere. Transport from each of these source regions show distinctive annual cycles related to the northeasterly Asian monsoon and the southeasterly trade wind maximum over Kenya in May. The Saharan transport in the lower troposphere is at a maximum when the subtropical high over northern Africa is strongly developed in the boreal winter. Air reaching Kenya between 700 and 500 hPa is mainly from Sahara and northwest Indian Ocean in the months of January and March, which gives way to southwest Indian Ocean flow in May and November. In contrast, air reaching Kenya at 400 hPa is mainly from southwest Indian Ocean in January and March, which is replaced by Saharan transport in May and November. Transport of air from Kenya is invariant, both spatially and temporally, in the tropical easterlies to the Congo Basin and Atlantic Ocean in comparison to the transport to the country. Recirculation of air has also been observed but on a limited and often local scale and not to the extent reported in southern Africa.

Aerosol optical depth over a remote semi-arid region of South Africa from spectral measurements of the daytime solar extinction and the nighttime stellar extinction

Abstract Spectral daytime aerosol optical depths have been measured at Sutherland, South Africa (32°22′S, 20°48′E), from January 1998 to November 1999. Sutherland is located in the semi-arid Karoo desert, approximately 400-km northeast from Cape Town. The site, remote from major sources of aerosols, hosts the South African Astronomical Observatory (SAAO), where nighttime stellar extinction is being measured. The comparison of daytime and nighttime measurements for the years 1998–1999 makes it possible to validate the astronomical dataset of aerosol optical depth ( τ a ) dating back to 1991. The 1998 and 1999 annually averaged daytime τ a at 500 nm are 0.04±0.04 and 0.06±0.06, respectively. Half-day averages vary between 0.03 and 0.44, with peak values in August–September. This pronounced seasonality is linked to the biomass-burning season in the Southern Hemisphere. Smoke haze layers transported to Sutherland originated primarily on the African landmass at latitudes between 10° and 20°S and passed over Namibia and Angola. On one occasion, aerosols from fires in Brazil transported across the Atlantic Ocean were likely detected. The haze layers reaching Sutherland are therefore at least 2–3 days old. The spectral dependence of the aerosol optical depth for the smoke layers supports the bimodality of the volume size distribution for biomass burning aerosols. The accumulation mode has a volume modal diameter of 0.32 μm, consistent with the hypothesis of aged haze. The stellar measurements (1991–2001) show that, due to the eruption of Mt. Pinatubo, the atmospheric extinction depth at 550 nm in the years 1991–1993 increased by 33% with respect to the average value (0.14±0.03) for the period 1994–2001. Outside the Pinatubo event, extinction is largest in the period 1997–1999.

Tropospheric carbon monoxide measurements from the Scanning High-Resolution Interferometer Sounder on 7 September 2000 in southern Africa during SAFARI 2000

Retrieved tropospheric carbon monoxide (CO) column densities are presented for more than 9000 spectra obtained by the University of Wisconsin-Madison (UWis) Scanning High-Resolution Interferometer Sounder (SHIS) during a flight on the NASA ER-2 on 7 September 2000 as part of the Southern African Regional Science Initiative (SAFARI 2000) dry season field campaign. Enhancements in tropospheric column CO were detected in the vicinity of a controlled biomass burn in the Timbavati Game Reserve in northeastern South Africa and over the edge of the river of smoke in south central Mozambique. Relatively clean air was observed over the far southern coast of Mozambique. Quantitative comparisons are presented with in situ measurements from five different instruments flying on two other aircraft: the University of Washington Convair-580 (CV) and the South African Aerocommander JRB in the vicinity of the Timbavati fire. Measured tropospheric CO columns (extrapolated from 337 to 100 mb) of 2.1 x 10(exp 18) per square centimeter in background air and up to 1.5 x 10(exp 19) per square centimeter in the smoke plume agree well with SHIS retrieved tropospheric CO columns of (2.3 plus or minus 0.25) x 10(exp 18) per square centimeter over background air near the fire and (1.5 plus or minus 0.35) x 10(exp 19) per square centimeter over the smoke plume. Qualitative comparisons are presented with three other in situ CO profiles obtained by the South African JRA aircraft over Mozambique and northern South Africa showing the influence of the river of smoke.

Smoke and Clouds above the Southeast Atlantic: Upcoming Field Campaigns Probe Absorbing Aerosol’s Impact on Climate

1 Campaigns Probe Absorbing Aerosol’s Impact on Climate 2 Paquita Zuidema∗ 3 University of Miami, Miami, Florida 4 Jens Redemann 5 NASA AMES Research Center, Mountain View, California 6 James Haywood 7 University of Exeter, Exeter, United Kingdom 8 Robert Wood 9 University of Washington, Seattle, Washington 10 Stuart Piketh 11 North-West University, Potchefstroom, South Africa 12 Martin Hipondoka 13 University of Namibia, Windhoek, Namibia 14 Paola Formenti 15 Laboratoire Interuniversitaire des Systemes Atmospheriques, Creteil, France 16