While the overall global uncertainty in sulfur dioxide emissions is relatively small, regional uncertainties ranged up to 30%. The largest contributors to uncertainty at present, the authors said, are emissions from China and international shipping. Emissions were distributed on a 0.5° grid by sector for use in coordinated climate model experiments.

Anthropogenic emissions have resulted in greatly increased sulfur deposition and atmospheric sulfate loadings near most industrialized areas. Sulfuric acid deposition can be detrimental to ecosystems, harming aquatic animals and plants, and damaging to a wide range of terrestrial plant life. Sulfur dioxide forms sulfate aerosols that have a significant effect on global and regional climate. Sulfate aerosols reflect sunlight into space and also act as condensation nuclei, which tend to make clouds more reflective and change their lifetimes, causing a net cooling. The radiative forcing change wrought by sulfate aerosols may be second only to that caused by carbon dioxide, albeit in the opposite direction [i.e., cooling].

Sulfur is ubiquitous in the biosphere and often occurs in relatively high concentrations in fossil fuels, with coal and crude oil deposits commonly containing 1–2% sulfur by weight. The widespread combustion of fossil fuels has, therefore, greatly increased sulfur emissions into the atmosphere, with the anthropogenic component now substantially greater than natural emissions on a global basis.

—Smith et al.

To determine how much sulfur has been emitted between the approximate beginning of the Industrial Age, 1850, and 2005, Steven Smith of the Joint Global Change Research Institute in College Park, Md.—a collaboration between the Department of Energy’s Pacific Northwest National Laboratory and the University of Maryland—and colleagues analyzed data about sulfur-emitting activities such as coal burning, copper smelting, or the use of petroleum. The data came from more than 140 countries and went back as far as the 1800s, when publications even at that time tallied how much coal and copper were produced.

The team collected the datasets, evaluated the quality of the records and plotted the data over time, breaking them down by region, source—such as coal or oil burning—and economic use such as heating or cooking, power production, and others.

The team estimated emissions data both by calculating sulfur release based on how much was contained in sources as well as from actual data on emissions collected from modern power plants.

Global petroleum emissions from the present inventory compared to estimates from a global crude oil mass balance using two different assumptions for the fraction of total sulfur retained in non-combusted products. The inventory data include terrestrial and international shipping combustion and process emissions from refineries. Also shown is the estimated global amount of sulfur removed at refineries (as Gg SO2). Credit: Smith et al. Click to enlarge.

The factors that determine total emissions are the amount of fuel consumed, its sulfur content, and any pollution controls employed. The team found that manmade sources of sulfur emissions eclipsed natural sources by 1870, two decades after the start date of this analysis. By the year 2000, however, refineries were removing half the sulfur from crude oil, reducing emissions, the researchers estimated.

Since 1980, the fraction of sulfur coming from petroleum (50%) and coal (30%) has remained constant. In a reflection of desires for cleaner fuels, emissions as a fraction of fuel consumption began decreasing around 1970, due to shifting to lower sulfur fuel sources, different end uses, and emissions controls.

Total global emissions rose dramatically from 1850 to the 1960s, plateaued and then decreased after 1990, and then started rising again in 2000. Although the contribution from major emitters of the past—North America and Europe—has been declining since the 1970s, sulfur emissions are rising in much of the rest of the world. Especially noteworthy is China with its phenomenal growth. By 2005, China’s share of sulfur emissions came in at 28% of the global total, up from about 2% in 1950.

The international shipping industry generally uses a lower quality, higher sulfur content fuel than other transportation modes, and emissions from this activity have been growing in importance. They now constitute 10% of the global total. Although rising during the study’s time frame, a recent international agreement (MARPOL) promises to reduce these emissions in future years.

This work was supported by the US Department of Energy’s Office of Science.

Resources

• S. J. Smith, J. van Aardenne, Z. Klimont, R. J. Andres, A. Volke, S. Delgado Arias (2011) Anthropogenic Sulfur Dioxide Emissions: 1850-2005, Atmospheric Chemistry and Physics, doi: 10.5194/acp-11-1101-2011