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Monitoring the Air and Rain

2010 April 21

As we’ve mentioned several times in this discussion forum over the past few weeks, the Acid Rain Program has been called the most successful environmental program in the past 40 years. We heard yesterday about how using continuous emission monitoring systems (CEMS) and other methods that measure the pollution that comes out of smokestacks gave us confidence that power plants were reducing pollution. But how do we know that those emission reductions are translating to better air quality and reductions in acid rain? In today’s blog, I’m going to talk about air monitoring and how EPA tracks changes in the chemistry of the air and of rainfall in order to show that the Acid Rain Program is actually having an effect – air quality is improving and acid rain is declining.

To track results of the program, EPA relies on data from two monitoring networks: the National Trends Network of the National Atmospheric Deposition Network (NADP/NTN) and the Clean Air Status and Trends Network (CASTNET).

NADP/NTN is a national, long-term monitoring network that began in the late 70s and collects and analyzes data from wet deposition – the rain, snow, fog, sleet, etc. that falls to the ground after coming in contact with pollution.  NADP’s more than 240 sites are operated by a collaboration of federal state, local and tribal government agencies; educational institutions; private companies; and non-governmental agencies.

CASTNET is a national, long-term monitoring network run by the EPA’s Clean Air Markets Division. It began in 1991 under the Clean Air Act Amendments, which created the Acid Rain Program, with the goal of assessing trends in air quality and also dry deposition – the dry dust, gases, and particles that fall to the ground after coming in contact with pollution. Many of the CASTNET sites have been around for a lot longer, with over 40 sites that have collected data for more than 15 years! Most of CASTNET’s 84 monitoring sites are located in rural areas around the country, where the influence from urban areas on pollution levels does not dominate the data. Twenty-five of these sites are located in national parks and other areas which need special protection from air pollution.

EPA doesn’t operate the NADP and CASTNET sites and so we rely on dedicated site operators around the country who actually go out to the monitoring station and collect the filter packs (which collect the dry deposition data from the air) and buckets (which collect wet deposition data from rainfall). One of the longest working and best known CASTNET site operators is Tom Butler from the Cary Institute of Ecosystem Studies and Cornell University. I had a conversation with Tom recently to talk about his experience with CASTNET.

Tom Butler has worked on acid rain since the mid-70s when he began working with Gene Likens, a pioneer in the study of acid rain. Most of Tom’s work focused on the chemistry of rainfall and air related to pollutants. He was particularly interested in how changing emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) affected the environment. He has been involved with CASTNET since its beginning and with its predecessor and has been collecting and analyzing data at his site, one of the originals, since the late 70s.

I asked Tom what it was like to operate a CASTNET site for so long. I was surprised to learn that even after 30+ years and a reputation as one of the leading scientists in his field, Tom is the one who drives out to the remote site southwest of Ithaca, NY (through rain or multiple feet of snow!) to collect the samples. And it’s clear that he loves this part of the job. He says it’s great to get out from behind a desk and a computer…something I can certainly appreciate!

Tom Butler

Connecticut Hill CASNTET monitoring site

But it’s also clear that Tom believes in the importance of his work. He noted that we spend billions of dollars on pollution control devices to reduce emissions at power plants so it’s equally important that we also invest some money in monitoring networks to study the impact of these pollution controls. The money spent on monitoring is small compared to the cost of reducing emissions, but well spent and achieves a lot of bang for the buck. The bottom line is that, through air and rainfall chemistry monitoring networks like CASTNET, we’ve been able to demonstrate that reducing SO2 and NOx emissions has reduced acid deposition by more than ½ in much of the eastern U.S. Monitoring might not be a sexy chunk of science, Tom explains, but it is vital. I couldn’t agree more.

What do you know about the CASTNET or NADP/NTN monitoring networks? Why do you think they are important? Tell us about your experiences with air or rainfall monitoring.

Erika Wilson works in communication for the Clean Air Markets Division in the Office of Air and Radiation.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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One Response leave one →
  1. April 21, 2010

    It would be helpful for EPA to address in this blog what’s happened to the value of SO2 allowances over the past few years, and over the past few months. Since early 2008, spot price has dropped from over $500 to less than $25. Just this year, values have dropped by over 50%. Facilities that purchased allowances to cover their emissions have taken a bath. And there’s no assurance that current allowances will continue to hold value under pending new rules.

    While we’re glad to see the significant progress with acid rain reduction, we need to question the market-based approach to allowance valuation. Especially since new CO2 requirements may be designed follow the Acid Rain model. We should also question the continued allowance allocations to older, less efficient plants, while the cleaner new plants must take their chances by purchasing allowances in an extremely volatile market.

    To stimulate investment in cleaner, more efficient power, we would hope for a greater degree of certainty than the market-based approach has provided.

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