Source terms and source strengths of the carbonaceous aerosol in the tropics

Abstract

Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6°N, 5°W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (13C/t2C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 20 x 10 t2 g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics.

Influence of production variables and starting material on charcoal stable isotopic and molecular characteristics

“…However, growing evidence suggests an offset in δ 13 C between the initial plant tissues and charcoal. Following heating over 100°C, δ 13 C values are elevated by up to 3.5‰ in bulk soil organic carbon, 2.0‰ in carbonized vegetation, 1.5‰ in plant propagules and 1.9‰ in wood (Cachier et al, 1985;Turekian et al, 1998;Werts and Jahren, 2007;Poole et al, 2002;Krull et al, 2003). In other work however, decreases of up to 1.8‰ have been observed in wood charcoal following heating up to 800°C (Jones et al, 1993, Czimczik et al, 2002Turney et al, 2006).…”

Natural Background Visibility and Regional Haze Goals in the Southeastern United States

“…29,30 The tropospheric burden of fine particulate carbon in low-latitude regions of the globe is dominated by long-range transport from the tropics. 31 A visible manifestation of biogenic organic aerosol is the blue haze often observed over forested regions, which results from oxidative particle formation, probably from biogenic terpenes. It is unclear, though, to what extent such secondary terpenoid aerosols contribute to the total biogenic organic aerosol burden.…”

“…Measurements of submicrometer (Ͻ1 m) PM in an equatorial forest in the Ivory Coast (west coast of Africa) found the average particulate carbon concentration (i.e., before multiplication by a factor, such as the 1.4 used by EPA and IMPROVE) to be 9 g/m 3 during the wet (growing) season. 31 Because biomass burning, which would have contributed carbonaceous particles during the dry season, did not take place during the wet season, the measured particulate carbon was attributed to natural emissions from the forest.…”

Evaluation of δ13C in Carbonaceous Aerosol Source Apportionment at a Rural Measurement Site

“…These effects can be direct, such as increased scattering or absorption of incoming solar radiation, or indirect by increasing light scattering caused by altered cloud properties (Twomey, 1974;Albrecht, 1989). Black carbon (BC), and more recently brown carbon (BrC), have been shown to absorb light, thereby contributing to climate warming (Bond (expressed as δ 13 C) has been widely used to characterize the sources of atmospheric aerosol (Chesselet et al, 1981;Cachier et al, 1985;Cachier, 1989;Widory, 2006;Cao et al, 2011;Kawashima and Haneishi, 2012). Common sources of aerosols have specific isotopic signatures, but variation in δ 13 C in aerosols from different sources can depend on many factors.…”