The Taipei Department of Environmental Protection yesterday recommended imposing an air pollution tax on jet fuel producers following an investigation showing that aviation emissions at Taipei International Airport (Songshan airport) are much higher than those produced by scooters and automobiles combined.

The study, funded by the Environmental Protection Administration (EPA), found that the 60,647 flights that passed through the airport last year produced 218,000 tonnes of sulfur dioxide, compared with 140,000 tonnes for scooters and automobiles.

As fumes discharged by airplanes freeze at high altitudes, the study targeted fumes produced by planes operating below 3,000 feet (910 m) and covered sulfur dioxide emitted during takeoff and landing, department Commissioner Liou Ming-lone said.

The study also found that the sulfur content in jet fuels produced by Formosa Petrochemical Corp, one of the two jet fuel refiners in the nation, averaged 1,400 parts per million (ppm), which is significantly higher than CPC Corp's average of 400 ppm.

Liou said that although neither firms exceeded the legal limit on sulfur content in jet fuel -- which is set at 3,000 ppm -- sulfur concentrations in Formosa Petrochemical's fuel were far higher compared with those by international refiners of the Pacific Rim, which the non-profit Coordinating Research Council said ranged from 348 ppm to 830 ppm in 2005 to 2010.

The department will recommend that the EPA, as stipulated in the Air Pollution Control Act levy an air pollution tax on airplane jet refiners, similar to the fuel tax collected from motorists, he said.

The tax revenue can be used by municipalities that have airports -- such as Taoyuan, Taichung, Tainan, Hualien and Taitung -- to research policies and measures to improve air quality in areas close to airports, Liou said.

The department would also recommend that the Bureau of Standards, Metrology and Inspection tighten the standards on sulfur content in jet fuel, he said.

Liou said that Formosa Petrochemical has promised to cut the sulfur content in its jet fuel to 1,100 ppm before March, but added that as sulfur levels are mainly affected by the manufacturing process, the firm would have to purchase hydro-desulfurization equipment if it wants to reduce sulfur content.

Sulfur dioxide can give rise to acid rain, which could cause soil acidification and damage freshwater ecosystems over extended periods, the department said.