Anthropogenic contributions to the carbonaceous content of aerosols over the Pacific Ocean

Abstract

Listen

Translate article

During a joint U.S./U.S.S.R. research cruise from 3 May to 27 July 1987 both total and fine (< 2 μm) particulate material was sampled. This cruise started in the Hawaiian Islands and then proceeded to the Kamchatka peninsula, south to Wellington, New Zealand, south of Australia into the Indian Ocean, to Singapore and then returned to the Hawaiian Islands by sailing just north of the Equator. Particulate samples, collected on quartz fiber and Teflon filters, were analysed for organic and elemental carbon by transmission thermo-optical carbon analysis and for trace elements by energy dispersive X-ray fluorescence. In the Northern Hemisphere the total particulate, organic carbon and elemental carbon concentration ranges were, respectively, 10–25, 0.5–2.5 and 0–0.3 μg m −3. In the Southern Hemisphere they were, respectively, 5–10, <0.6 and <0.02 μg m −3. In the Northern Hemisphere the fine particulate concentration range was 2–15 μg m −3 and the fine fraction varied from 20 to 80% of total aerosol loading. In the Southern Hemisphere the fine particulate loading was 1.2–1.7 μg m −3 and was usually less than 20% of the total particulate mass. Chemical mass balance (CMB) modeling was used to determine possible anthropogenic particulate contributions to the ocean aerosol. Readily available source profiles were used for CMB modeling. Sea-salt aerosol was represented by either the conventional EPA marine source profile or by the average of ambient ocean aerosols sampled in very clean mid-ocean regions. Usually 60–90% of ambient particulate mass was “explained” by the CMB model. Sources such as soil, catalytic auto emissions and wood-burning emissions were found to be possible contributors to the ocean aerosol, especially in the Northern Hemisphere. Anthropogenic contributions were estimated to contribute from 10 to 30% of oceanic aerosol mass. Emissions from a hugh forest fire that burned in northern China during the spring of 1987 were possibly detected, but the CMB model cannot distinguish this source from emissions from heating and cooking with wood. Since anthropogenic emissions are mainly combustion emissions which usually contain a large carbon component, carbon data is essential to CMB modeling. The relatively good CMB results obtained in this study suggest that it might be useful to develop source profiles for major emission sources in those countries which contribute most directly to oceanic aerosols. Perhaps characteristic national or regional source profiles could be developed.