Where Air Quality and Climate Change Meet

As Woods Hole Oceanographic Institution research vessel Atlantis chugged up the coast off La Jolla in June, a particularly fecund red tide happened to be rendering the local surf pink and frothy.

And in the sky above a marine layer gathered enough strength to dim the sun slightly at the onset of a Southern California summer that would be known for its relentless grayness.
The people on the vessel, including Amanda Frossard and Cassie Gaston from Scripps Institution of Oceanography, UC San Diego, were curious to see if the invasion of dinoflagellates that caused the red tide was also behind the thickening of the marine layer.

Woods Hole Oceanographic Institution research vessel Atlantis gathers air samples off Scripps Pier, It wouldn’t be the first time that local weather was influenced by microbial ocean dwellers. In fact, aerosols of all kinds — from sea spray to diesel exhaust — that are released from land and sea into the sky have a major influence on climate in and coastal regions around the world. Defining their role in air quality and understanding how they scatter light and impact cloud formation once airborne has been, however, one of the toughest challenges of the past decade to the atmospheric chemistry community.To help fill in details, Scripps researchers joined colleagues from 15 other research centers on the NOAA-led project CalNex. From several ground locations throughout California and Tijuana, Mexico, from aircraft and Atlantis, project participants sought to create a comprehensive survey of pollution in the state.

“That makes CalNex pretty exciting,” said Frossard. “This is a big push to look at air quality and climate change in California.” 

Lynn Russell, an atmospheric chemistry professor at Scripps and a CalNex principal investigator, said the project could be the most comprehensive study of aerosols and pollution done anywhere to date.

“It should provide a great guideline for us about sources of particles as well as their impact,” she said. “It’ll give us an idea of the variety of the aerosols in California.”

Gaston, a student of UCSD atmospheric chemistry professor Kim Prather, and   Frossard, a student of Russell, analyzed particles in different ways. While Frossard gathered them on filters to acquire overall organic composition of particles during given time periods, Gaston analyzed the chemical composition of individual particles to determine which natural and human sources were impacting the marine boundary layer and determine how long they had been airborne. Land and aircraft measurements allowed for comparisons of the state’s airborne aerosols across multiple spatial dimensions. 

“Using all these different techniques will hopefully help us get a more cohesive picture of how we impact our local climate,” Gaston said.

After collecting field data in May and June, the researchers are in the middle of analysis that could start yielding conclusions by early 2011. Russell said that an expected report to the California Air Resources Board, which funded a portion of the CalNex study that took place in Bakersfield, could help to shape air quality regulations in the future.

Prather’s group flew sampling instruments on two research aircraft during the CalNex campaign.  At the beginning of the study, the team flew an instrument on a Twin Otter plane from Ontario, Calif. and at the end of the study sampled on the DOE G1 aircraft out of California. 

“Understanding how ocean-generated aerosols mix with air pollution at all levels of the atmosphere from other manmade sources is critical to understanding their overall impact on regional climate and air pollution in California,” said Prather. 

Atlantis, which sampled air up the coast from San Diego to the Sacramento River delta, gathered a cross-section of California’s coastal air from the congestion of America’s busiest commercial port in Long Beach to the open ocean and to the plumes of exhaust given off by cargo ships at sea. Around the same time, ground stations in Bakersfield and Pasadena vacuumed in ambient air samples that occasionally provide local color to their regional air. While Pasadena samples gathered by Russell’s graduate student Ashley Corrigan contained particles that would be expected to be found from the vehicle exhaust dominating an urban area’s pollution mix, Bakersfield’s — collected by Shang Liu, another student in Russell’s lab — contained often high concentrations of filter-darkening agriculturally-based particles, such as those caused by burning crop waste. Air samples gathered at the Tijuana station (in an associated project called CalMex) revealed the signatures of trash burning and the still-frequent use of older cars and trucks in the Mexican border city.

Atlantis gathered hints of urban smog that blew out to sea and combined with particles from natural sources to influence the marine layer in ways not yet understood.

“Even just from looking at the filters, it was very clear what days we were getting clean air and what days had a lot of pollution. The filters looked totally different, with the filters from the polluted days much darker than the clean days,” Frossard said. “But they still weren’t as dark as Bakersfield.”  

--Robert Monroe