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Ask AP: Jet pollution, fraction-of-a-cent coins
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    It can be a manufacturing plant, a spice grinder or a place where rumors get started. But did you know a ‘‘mill’’ can also be one-tenth of a cent — a unit of currency that showed up on state-issued tokens in the 1930s?
    A reader’s recollection that he once saw a 10-mill coin inspired one of three questions in this edition of ‘‘Ask AP,’’ a weekly Q&A column where AP journalists respond to readers’ questions about the news.
    If you have your own news-related question that you’d like to see answered by an AP reporter or editor, send it to newsquestions(at), with ‘‘Ask AP’’ in the subject line. And please include your full name and hometown so they can be published with your question.
    What happens to all the jet fuel exhaust that’s deposited high in the atmosphere, where airliners and other aircraft fly? Given the amount of fuel the world’s jets collectively consume — and the fact that the temperature is well below zero at an airliner’s typical cruising altitude — it seems unlikely that the exhaust would just harmlessly dissipate.
    So where does it all end up? Is there a growing layer of spent fuel around the planet at 35,000 feet? And is this contributing to global warming?
    Michael A. Terminiello
    Plantsville, Conn.
    Just like car engines, jet engines burn fossil fuels and produce emissions that add to global warming. And they are spewed at higher altitudes, which increases the heat-trapping properties of the pollution, according to the Intergovernmental Panel on Climate Change.
    In 1999, this panel of international scientists produced a special report on airplanes and global warming. It found that airplane emissions add to global warming directly by producing the chief man-made global warming gas, carbon dioxide. That’s the biggest global warming effect from planes — and it’s relatively small compared with the net effect from power plants and cars, said Jerry Mahlman, a retired top federal climate scientist and expert on the upper atmosphere.
    Airplanes’ condensation trails, or ‘‘contrails,’’ also contribute to global warming. And planes spew nitrogen oxides, which increase the global warming effect of ozone in the atmosphere — but also fight global warming a bit by reducing the amount of methane in the atmosphere.
    In 1992, airplanes were responsible for about 3.5 percent of the global warming effect, according to the science panel. But the group predicted that by 2050 that figure would increase to 5 percent.
    And no, planes don’t produce their own stratospheric belt of carbon dioxide — they don’t fly high enough for that to happen. Instead, jet emissions mix with all the other carbon dioxide produced closer to the ground, Mahlman said.
    Seth Borenstein
    AP Science Writer, Washington
    In a previous edition of Ask AP, you said the U.S. never issued ‘‘mill’’ currency, or tenths of a cent. But I remember seeing a 10-mill piece when I was 12 years old. Who issued these coins?
    Ray Morse
    Spring, Texas
    ‘‘Mill’’ coins — more commonly known as sales tax tokens — were issued by some states beginning in the mid-1930’s to allow for exact payment of taxes of less than one cent. States issuing the coins included Arizona, Colorado, Illinois, Kansas, Louisiana, Missouri, New Mexico and Washington.
    The tokens were known by all sorts of nicknames — like Tom Thumbs, sub-pennies, midgets, pygmy coins and molecule money. Some Kentuckians who used them to pay sales taxes called them rubies, after then-Gov. Ruby Laffoon. In Missouri, where the disks were made of cardboard, they were known as ‘‘milk bottle cap tokens.’’
    Some people came up with novel uses for mill tokens, leading to shortages of the coins. Arizona jewelers used them for bracelets, belts and watch fobs, and bridge players used them as counters. And the tokens from Kansas, it turns out, were a perfect fit for dime slot machines.
    Decades have passed since mill currency was last used — thanks to inflation, there simply isn’t any practical need to collect sales taxes that amount to a fraction of a penny.
    Judy Ausuebel
    AP News Research Center
    There has been talk of the airlines upgrading their tracking systems to GPS, in part to speed up passengers’ travel times. My question is this: How will GPS make flight delays a thing of the past? Sure, you might be able to get more planes in the air, but won’t crowded airport runways still be a problem?
    Thomas McAfee
    Little Rock, Ark.
    Replacing ground-based radar with the Global Positioning Satellite system is the heart of the Bush administration’s multi-billion-dollar proposal to redesign air traffic control. By giving controllers and pilots more accurate location information, the distances now required between aircraft can be reduced.
    This would allow more flights in the air at once — but would not by itself end flight delays.
    Air traffic controllers and other experts agree the number of available runways limits how many planes can fly at once and is a key contributor to flight delays.
    Michael Sniffen
    AP Transportation Writer, Washington
    Have questions of your own? Send them to newsquestions(at)

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