Airplane pollution, reusing shoes and biomass energy. (Ask E).

Do airplanes contribute significantly to air pollution?--Neil Gladstone, New York, NY

Airports cause as much pollution as power plants, incinerators and oil refineries, although they are subject to less regulation, according to the Natural Resources Defense Council (NRDC). The hundreds of thousands of airplanes taking off, landing, taxiing and idling each day across the country create smog, contribute to global warming and severely impact local air quality.

Major airports rank among the top 10 industrial air polluters in many cities and have been linked to health problems from asthma to cancer. A 1999 report by the Intergovernmental Panel on Climate Change (IPCC) found that aircraft are responsible for 3.5 percent of greenhouse gas emissions worldwide; this could increase to 10 percent by 2050 as the popularity of air travel rises.

Because airplanes are considered part of interstate commerce, they are not subject to local and state pollution laws. Furthermore, the Federal Aviation Administration has the potentially conflicting responsibilities of monitoring pollution and promoting air travel. Despite a lack of governmental control, however, Delta Air Lines has voluntarily reduced engine idling, thereby cutting ground-level air pollutants up to 40 percent.

Meanwhile, NRDC promotes fuel taxes as a way to encourage airlines to increase their efficiency. In Britain, legislators hope to promote train travel as an alternative with higher taxes on aviation. Even so, airplanes that are at least 70 percent full are still more fuel-efficient than other means of travel, including automobiles and trains. CONTACT: IPCC, www.ipcc.ch; NRDC, [phone], www.nrdc.org.

Are there ways to recycle old athletic shoes?--Carmen Wolf, Los Angeles, CA

For folks with athletic shoes headed for the landfill, Nike has established the Reuse-a-Shoe program. Since it began in 1993, the program has recycled some 13 million pairs of athletic shoes into surfaces such as soccer, football and baseball fields, weight room flooring, synthetic basketball and tennis courts, playground tiles and floor padding. The program accepts all athletic shoes as long as they don't contain any metal. The Nike website offers a list of collection locations as well as an address to which old shoes can be mailed. The company also hopes to eventually recycle old shoes into new ones.

The Clean Washington Center is another organization researching athletic shoe recycling. The group is looking at manufacturing doormats and shoe soles out of recycled footwear.

For people with wearable athletic shoes they'd like to be rid of, there's also the option of donating sneakers to local charities and thrift stores. Some organizations, such as the Children's Rights Foundation (CRF), are making a significant effort to place used shoes where they are needed most. CRF accepts shoes at its Florida-based operation, and then distributes them to needy and at-risk children and their families within the U.S. and abroad. CONTACT: Children's Rights Foundation, [phone], www.crfi.org/retail.html; Clean Washington Center, www.cwc.org/tires/t971rpt.htm; Nike, [phone], www.nike.com.

What is "biomass energy" and where is it used?--Kourosh Khazaii, Vancouver, BC

Biomass refers to any plant matter used directly as fuel or converted into other forms of fuel before combustion. Unlike fossil fuels, which take millions of years to form, biomass is renewable in a short period of time. Biomass, when burned, emits less carbon dioxide into the atmosphere than gasoline or coal.

Developing countries generally use large amounts of biomass as fuel for cooking and heating, given their lack of access to other forms of energy. In the developing world, biomass makes up almost a third of total energy usage. In contrast, the U.S. uses biomass for only four percent of its total energy supply.

The International Energy Association (IEA) reports that biomass combustion could potentially grow from 11 percent of the world's energy supply to 40 percent. While many countries are making efforts to increase their biomass usage, Australia is generally recognized as a leader due to the close cooperation between government agencies, research facilities and industry. Some of Australia's foremost projects include the production of ethanol and methanol for use as liquid fuels and the use of combustible gases to power electric generators. Britain is also developing significant biomass projects. CONTACT: Biomass Energy Research Association, [phone], www.bera1.org; International Energy Association, (011)33-1-40-57-65-00, www.iea.org.

Send your questions about environmental issues, from the personal to the political, to Ask E, P.O. Box 5098, Westport, CT 06881, or e-mail [e-mail]. Please keep your questions brief. Include your full name, address and a daytime phone number.