NIST's natural air standards support accurate greenhouse gas measurements

February 19, 2016, National Institute of Standards and Technology
NIST's natural air standards support accurate greenhouse gas measurements
Standard Reference Material 1720 (Northern Continental Air), is based on samples collected in the Rocky Mountains. Credit: NIST/Bob Watters

When it comes to tallying emissions of greenhouse gases, there is no better substitute than directly measuring the atmosphere. But this important accounting can be obscured, and even confused, if measurements of the air-borne heat-trapping chemicals are inaccurate or can't be compared from one instrument or data set to the next.

To help ensure reliably accurate measurements of the big three long-lived greenhouse gases, the National Institute of Standards and Technology (NIST) has issued two new Standard Reference Materials (SRMs) that are puffs of naturally occurring from far-flung parts of the globe.

The new NIST-certified references—Southern Oceanic Air (SRM 1721) and Northern Continental Air (SRM 1720)—contain painstakingly measured concentrations of , methane and . They respond to the growing need for greenhouse gas calibration standards that extends beyond organizations participating in the World Meteorological Organization (WMO) Global Atmosphere Watch Program, including its North American network. This program is served by a dedicated set of calibration laboratories.

A variety of other organizations outside these official monitoring networks also measure greenhouse gases and need tools for ensuring accuracy. They include state and local agencies that track emissions and atmospheric concentrations of the gases; automobile manufacturers, which are particularly interested in leaks and other unintended emissions of nitrous oxide from vehicles; and so-called megacities projects that inventory sources and levels of the gases in large metropolitan areas.

To ensure measurement accuracy, these and other types of organizations can first use their instruments to measure concentrations of the three gases in a NIST natural-air SRM. If the results differ from the SRM's certified values, they can adjust—or calibrate—their instruments accordingly before measuring gas levels in the local atmosphere.

The two natural air benchmarks hold the NIST record for lowest uncertainties assigned to components in the agency's more than 60 primary gas SRMs.

The southern oceanic air hails from Baring Head, New Zealand, site of an air-monitoring station situated on a coastal cliff 79 meters above the Pacific Ocean. Samples were gathered in New Zealand at times in which prevailing winds originated from Antarctica.

Samples of northern continental air were collected during late winter and early spring seasons in the Rocky Mountains at Niwot Ridge, Colo., a forested area more than 3,500 meters (almost 11,500 feet) above sea level.

Standard Reference Material 1720

For nearly four decades, the National Oceanic and Atmospheric Administration (NOAA) has been siphoning the site's pristine air for its monitoring program and, more recently, for supplying calibrated reference samples to organizations participating in the WMO's atmospheric monitoring network and NOAA's tracking system.

NIST and NOAA independently measured concentrations of the three greenhouse gases in the volumes of northern continental air contained in aluminum gas cylinders. While the NIST and NOAA measurements were in close agreement, the SRMs' certified concentrations are taken from the actual NIST assigned values. The NOAA values are included for those users who need to use the WMO-accepted calibration.

Among long-lived greenhouse gases, the three compounds account for about 90 percent of what is known as "radiative forcing"—a measure of the compounds' influence on the balance of incoming and outgoing energy in the Earth-atmosphere system. Carbon dioxide, the most abundant greenhouse gas, accounts for 65 percent of radiative forcing. Molecule for molecule, methane (at 17 percent) and nitrous oxide (6 percent) are much stronger absorbers of the Earth's reradiated energy, but they are less abundant in the atmosphere.

Accurate measurements of known and suspected influences on climate change require a sophisticated, underpinning infrastructure. NIST research chemist George Rhoderick says certifying concentrations of the three in both natural air SRMs first required developing a set of even more exacting primary standards for each gas. The NIST Gas Sensing Metrology Group, he explains, spent five years developing suites of these primary standard mixtures so that measured NIST-certified concentrations of each gas in the SRMs is linked to the global measurement system.

For both natural-air SRMs, pressurized canisters containing the mixture have been calibrated individually. Average values are 390.1 parts per million for carbon dioxide and 0.32 parts per million for nitrous oxide. Average methane values differ by about 6 percent—1.7 parts per million for the southern ocean air mixture and 1.8 parts per million for cylinders of northern continental air.

To learn more about the new SRMs, visit their pages at SRM 1720-Northern Continental Air and SRM-1721-Southern Oceanic Air.

Explore further: Scientists blend synthetic air to measure climate change

Related Stories

Scientists blend synthetic air to measure climate change

February 26, 2014

Scientists at the National Physical Laboratory (NPL) have produced a synthetic air reference standard which can be used to accurately measure levels of carbon dioxide and methane in the atmosphere. This will greatly help ...

New website to monitor greenhouse gases

June 20, 2011

An Australian research institute on Monday launched a website that allows the public to monitor greenhouse gas emissions in the southern hemisphere.

NASA takes part in airborne study of Antarctic seas

January 29, 2016

A team of scientists has launched a series of research flights over the remote seas surrounding Antarctica in an effort to better understand how much carbon dioxide the icy waters are able to lock away.

Recommended for you

Rainfall's natural variation hides climate change signal

February 22, 2018

New research from The Australian National University (ANU) and ARC Centre of Excellence for Climate System Science suggests natural rainfall variation is so great that it could take a human lifetime for significant climate ...

Seasonal patterns in the Amazon explained

February 22, 2018

Environmental scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have led an international collaboration to improve satellite observations of tropical forests.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.