Rainwater Chemistry: What’s in Precipitation, and Why Does It Matter?

National Atmospheric Deposition Program monitoring equipment

National Atmospheric Deposition Program monitoring equipment

Chemicals are integral to human technology and enterprise. While chemicals such as ammonia, mercury, and nitrogen are also part of natural processes, they can occur at artificial levels in the earth’s water, soil, and atmosphere due to human influence. When these concentrations become too high, they can affect human and environmental health, water quality, agriculture, family and rural development, and more.

For more than 40 years, the National Atmospheric Deposition Program (NADP) has monitored North America’s precipitation and atmosphere for a range of pollutants, and the data are used to determine trends in pollution concentration over time and across geographic areas. Precipitation samples are sent to a central laboratory for testing.

According to Michael Olson, NADP Coordinator, “long-term monitoring is key to understanding how emissions impact ecosystems and the built environment. NADP’s unique dataset allows policymakers and researchers to make informed decisions about environmental health. Just as important, it gives us a way to measure the effectiveness of policies implemented to address these issues.”

NADP has several hundred monitoring stations across North America. The Arboretum, with a long history of ecological monitoring, has recently become a site for NADP equipment that will collect valuable data for the program. The instruments installed this winter at the Arboretum include:

  • bucket samplers to measure nutrient chemicals (such as nitrate, sulfate, and ammonium) and mercury in rainwater
  • a real-time rain gauge to calculate wet deposition, the transfer of pollutants to the ground through precipitation
  • a passive sampler to measure ammonia in the atmosphere and determine the dry deposition to the ground and plant surfaces

Data collected from this station provides an opportunity to link atmospheric chemistry to changes in patterns of plant and animal diversity, soil organisms, and water quality in long-term ecological restoration.

Olson says the Arboretum site is valuable for several reasons. “Working with Arboretum experts, we can identify links between precipitation chemistry and changes we see in ecosystems. In addition, the Arboretum’s NADP site is a great location for the public to learn how data collection and analysis help scientists understand the impact of human activities on the environment we all live in and care about.”

NADP started amid concerns about acid rain in the United States and continues to monitor long-term impacts of acid rain around the world. The program also monitors mercury and ammonia in precipitation and continues to respond to emerging issues, such as airborne allergens.

NADP, housed at the Wisconsin State Laboratory of Hygiene at the University of Wisconsin–Madison, is a cooperative effort of many different groups including federal, state and local government agencies, Native American organizations, state agricultural experiment stations, universities, and non-governmental organizations. It is often considered the international gold standard for long-term high-quality air pollutant monitoring.

—Susan Day, communications coordinator

To learn more, visit the NADP website.