We tend to think of summer as prime time for pollution—picture the haze that hangs over big cities on hot, steamy days. That's when increased sunlight and temperatures speed up chemical reactions that transform pollutants in the air into other "secondary" pollutants, including ozone, particulate matter, and others. But pollution doesn't cease at summer's end. Instead, the pathways to these familiar summertime pollutants are altered in ways that haven't been well studied and that therefore aren't well understood.

Beginning in February, a team of researchers, including those from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder and NOAA’s Earth System Research Laboratories (ESRL) in Boulder, Colorado, will join colleagues from the National Center for Atmospheric Research (NCAR) and several universities in an airborne atmospheric chemistry experiment to remedy this gap. “I’m not aware of any recent campaign that examined air pollution in winter, from aircraft, with state-of-the-art instruments,” says José-Luis Jiménez, a CIRES scientist and one of the instrument’s principal investigators.

This experiment—Wintertime Investigation of Transport, Emissions, and Reactivity, or WINTER 2015—is a National Science Foundation (NSF)-funded, 6-week field campaign in the eastern United States that will take airborne measurements of atmospheric gases and particles that can affect air quality. From February 1 to March 15, scientists will use instruments on board the NSF/NCAR C-130 aircraft, based at NASA’s Langley Research Center in Hampton, Virginia, to sample several kinds of pollution sources in the mid-Atlantic and southeastern United States: large urban areas, coal-fired power plants, oil and gas extraction fields, agricultural or biofuel burning, and vegetation.

Though the researchers expect to see some familiar pollution-forming processes at work in the wintertime, they also expect differences.  For example, winter’s colder temperatures and reduced sunlight lead to a different mix of emissions than in summer, as agricultural activities shift and emissions produced by plants or animals are reduced. Instead, different trace gases almost certainly have larger, but unexplored, roles in wintertime pollution chemistry. “When we look at ozone chemistry in winter, the effects of pollutants on ozone production aren’t as clear,” says Steve Brown, a scientist with NOAA’s Earth System Research Laboratories and one of two WINTER lead scientists.

The cold also slows down the chemical transformations in the atmosphere. This slowed chemistry means that the main drivers of air pollution in the summer, such as sunlight triggering ozone production, are only minor players in winter. According to Brown, “the slower processes at work in winter mean that primary emissions stay longer in the  atmosphere, and disperse over wider areas as compared with summer, before they are removed by reactions.”

The CIRES and NOAA ESRL teams will operate three instruments on board the C-130 aircraft, to measure a suite of nitrogen-containing trace gases, ozone, sulfur dioxide, organic acids, and airborne particles.  Other teams will measure several other trace gases and solar radiation. Together, these observations will ultimately yield a rich data set that will enable the researchers to decipher the wintertime chemical pathways that transform primary emissions (such as methane and nitrogen oxides) into secondary pollutants (such as ozone and fine particles). See sidebar for the specific goals of the WINTER 2015 project.

Steve Brown and Joel Thornton of the University of Washington are the project’s principal investigators. Brown and Thornton will share flight scientist duties, which include developing daily flight plans and working on board during flights with the pilots and instrument scientists to achieve flight objectives. CIRES’ José-Luis Jiménez, along with several other university colleagues, are heading up teams in charge of the various instruments on board the aircraft. 

Ultimately, the findings from WINTER 2015 should help researchers better understand the impacts of wintertime processes on air quality and climate.

CIRES scientists at NOAA ESRL/CSD and NOAA ESRL/CSD scientists involved in the project are:  Steve Brown (Principal Investigator, NOAA ESRL), José-Luis Jiménez (Principal Investigator, CIRES), Patrick Veres (CIRES), Bill Dubé (CIRES), John Holloway (CIRES), Erin McDuffie (CIRES), Jim Roberts (NOAA ESRL), Dorothy Fibiger (NSF Geospace Sciences Post-Doctoral Fellow, NOAA ESRL), Pedro Campuzano-Jost (CIRES), Jason Schroeder (CIRES), Doug Day (CIRES), and Brett Palm (CIRES).

More on the web:

• NOAA ESRL Chemical Sciences Laboratory’s WINTER 2015 field mission page
• WINTER White Paper
• NCAR’s WINTER 2015 page
• University of Washington’s WINTER 2015 page

High-resolution images are available for download on CIRES’ Flickr account, News Release album

1. Researcher working inside the C-130 aircraft.
2. The NSF/NCAR C-130 research aircraft.
3. Suite of instruments inside the C-130 aircraft