A US new analysis of sulfur emissions appearing in the journal Atmospheric Chemistry and Physics shows that after declining for a decade, worldwide emissions rose between 2000 and 2005 due largely to international shipping and a developing economies.

An accurate read on sulfur emissions will help researchers predict future changes in climate and determine present day effects on the atmosphere, health and the environment.

Sulfur dioxide is a major air pollutant and has significant impacts upon human health. In addition the concentration of sulfur dioxide in the atmosphere can influence ecosytems. Sulfur dioxide emissions are a precursor to acid rain and atmospheric particulates.

The Industrial Age ushered in widespread combustion activities that emit sulfur compounds into the atmosphere. Sulfur dioxide has the potential to acidify rain, soil and lakes, and it can counteract some of the warming effect of carbon dioxide, making it an important component of the environment to understand.

Due largely to the US EPA’s Acid Rain Program, the U.S. has witnessed a 33 percent decrease in emissions between 1983 and 2002. This improvement resulted in part from flue gas desulfurization, a technology that enables SO2 to be chemically bound in power plants burning sulfur-containing coal or oil. This does not take into account the world's growth and other national sources.

In the air, Sulfur compounds can form particles called aerosols. Aerosol particles help form cloud drops, potentially changing rainfall amounts as well as affecting the acidity of the raindrops. Both clouds and the aerosols themselves reflect sunlight, reducing the amount of energy absorbed by the planet.

To determine how much sulfur has been emitted between the approximate beginning of the Industrial Age, 1850, and 2005, Smith 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 data sets, 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. In the United States, government agencies such as the Environmental Protection Agency and the Department of Energy collect such data.

The factors that determine total emissions are the amount of fuel consumed, its sulfur content, and any pollution controls employed. The team found that man made sources of sulfur emissions eclipsed natural sources by 1870, two decades after the start date of this analysis.

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 growth. By 2005, China's share of sulfur emissions came in at 28 percent of the global total, up from about 2 percent 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 percent of the global total.