Reactive Trace Gases

What are atmospheric reactive trace gases?

Reactive trace gases in the atmosphere can chemically alter other atmospheric gases, create or modify aerosols, and chemically alter surfaces they interact with. They are measured in units of mixing ratio, for example 'parts of reactive gas per million parts of air'. Many biological surfaces, from leaves to human lungs, can sustain damage when exposed to reactive trace gases. For this reason, the United States EPA or Environmental Protection Agency (and similar agencies in most other countries) has determined the reactive trace gases that are the most destructive, oversees the monitoring of these gases, and sets limits on the concentration of these gases which often requires controlling anthropogenic sources. The EPA has established a concentration‐based National Ambient Air Quality Standard for certain trace gases to protect human health. These criteria pollutants include ozone (O₃), carbon monoxide (CO), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂).

History of atmospheric reactive trace gases at Whiteface Mountain

Atmospheric trace gas research by the ASRC at Whiteface began in 1974 with the installation of a Thermo Environmental (TEI) continuous ozone analyzer at the Whiteface Summit Observatory in collaboration with the New York State Department of Conservation (DEC). ASRC's measurements of CO, SO₂, NO, NO₂ and total oxides of nitrogen began in earnest in the late 1980's to develop an understanding of atmospheric pollution chemistry and to quantify the efficacy of pollution control policy. Aerosol, precipitation, and cloud chemistry sampling complement the trace gas monitoring and collectively these observations contribute to our understanding of acid precipitation chemistry and the deposition processes of atmospheric pollutants. Currently, analyzers with enhanced sensitivity such as Thermo and Teledyne API trace-level instruments are in use with automated daily calibration checks further supported by weekly site visits. A gaseous elemental mercury (Hg) analyzer was installed in 2020 to monitor airborne Hg.

A second monitoring site near Marble Mountain Lodge was installed in 1990 in a collaboration between ASRC and DEC. Like the Whiteface Summit site, the four criteria pollutants O₃, CO, NO₂, and SO₂ are monitored as well as a variety of aerosol measurements. Three collaborative long‐term monitoring projects are also collocated at the Marble Mountain Lodge site. The National Atmospheric Deposition Program (NADP) has monitored precipitation quantity and chemistry at this site since 1984 with weekly samples shipped to their central analytic laboratory. Ammonia passive samplers were added in 2012 and are collected every other week. A Clean Air Status and Trends Network (CASTNET) tower was installed nearby in 2000 and moved to the present site in 2012. CASNET filter packs are collected weekly to monitor the dry deposition of aerosols. Meteorological observations are provided by the New York State MESONET since 2016. Like at the Whiteface Summit these aerosol, precipitation chemistry, and meteorological observations complement the trace gas monitoring in understanding atmospheric pollution.

Why is it important to study atmospheric reactive trace gases?

Criteria trace gases have a negative impact on human health and ecosystems worldwide. Nearly every country regulates these pollutants to address health and environmental effects; understanding trace gas transport and chemistry is critical in developing sound regulatory policy. The Adirondack Park has experienced widespread damage to forests, lakes, and streams from acidic precipitation whose primary source stems from the precursor trace gases NO₂ and SO₂. The Whiteface summit stands sentinel as the choice location at altitude in the Adirondack Park where trace gases, cloud and precipitation chemistry, and aerosols can be monitored and studied to understand the connection between long-range pollution transport and the deposition of acids on the environment. A remarkable recovery from acid rain is underway in the Adirondacks as a response to policy and informed regulation made possible by long-ter atmospheric monitoring and a developing understanding of atmospheric chemistry.