Although separate programs are in place to research and manage both air quality and climate change effects, these problems are not separate and in fact are intimately connected. These connections arise because in many cases the agents of concern are the same, and in many cases the sources of the agents are the same or intimately connected.

...For example, surface ozone is both an air pollutant and a greenhouse gas. Also, aerosols not only have significant climate impacts, but they also constitute particulate matter (PM), an important air pollutant, are responsible for visibility degradation, and are important agents in acidic deposition. In many cases, efforts to address one of these issues can be beneficial to the other, but in other cases policies addressing one issue can have unintended detrimental impacts on the other.

The complex roles that ozone and aerosols play in the atmosphere provide examples of such trade-offs. Reductions in the emissions of nitrogen oxides (NO_x) and/or volatile organic compounds (VOCs) to reduce ozone formation for improved air quality, also ameliorate climate impacts from ozone and VOCs. However, efforts to reduce emissions of PM and its precursors (SO₂, NO_x, VOCs, ammonia) for air quality improvement can lead to a further warming effect on the climate, because scattering of sunlight by aerosols masks as much as 50% of the present warming effect of greenhouse gases.

—2010 CalNex Science and Implementation Plan

In the CalNex 2010 study outlined here, NOAA researchers are studying several issues at the heart of the coupled air quality and climate change problems. California was chosen as the site for this first case study for a number of reasons, including its well-document air quality problems and leadership in addressing them, and in its efforts to address global climate change.

The CalNex collaborators have outlined a number of science questions for the project. They are intended to be 1) feasible to address in the context of the proposed study; 2) specific enough to provide a needed focus; but 3) general enough to cover the scientific issues of immediate policy interest. These questions fall into three broad categories: emissions; chemical transformation and climate processes; and transport and meteorology.

1. How can we improve the emissions inventory for greenhouse gases, ozone and aerosol precursors including emissions from soil, ships, agriculture and other non-industrial or transportation related processes?

2. What emissions (natural and anthropogenic) and processes lead to sulfate formation over California coastal waters and in urbanized coastal areas? What is the contribution from ship emissions? How does Southern California compare and contrast with the San Francisco Bay Area?

3. What sources and processes contribute to atmospheric mercury concentrations in California?

4. How important are chemical processes occurring at night in determining transport and / or loss of nitrogen oxides, reactive VOC and ozone? Do regional models in California adequately represent these processes and their effect on air quality? What measurements can help validate the use of satellite data for biogenic VOC and NO_x emission inventories?

5. What are the sources and physical mechanisms that contribute to high ozone concentrations aloft that have been observed in Central and Southern California?

6. Are there significant differences between Central Valley and South Coast Air Basin precursors or ozone formation chemistry? Will meteorological and/or precursor differences between the Central Valley and the South Coast Air Basin lead to different chemical transformation processes and different responses to emissions reductions? What is the importance of natural emissions to the ozone formation process? Are there regional differences in the formation rates and efficiency for particulate matter as well?

7. What are the impacts of aerosols in California on radiative forcing and cloud formation? What are the most important precursors and formation processes for secondary organic aerosol? What is the role of aqueous phase processes in atmospheric transformations?

8. What are proper oceanic boundary conditions for coastal and regional atmospheric chemistry modeling? Are there variations in oceanic boundary conditions in northern and central California vs. the southern part of the state? What physical and chemical changes occur as a parcel of air moves from off-shore, through the shore zone, and inland?

9. How best can we characterize and model air flow over coastal waters and the complex terrain of California? For example: what is the best representation of air flow in the southern San Joaquin Valley, particularly with respect to flow between the San Joaquin Valley and South Coast Air Basin versus recirculation north along the Sierra Nevada and Coastal ranges?

10. What are the major deficiencies in the representation of chemistry and meteorology in research and operational models and how can models be improved through the collection of additional measurements? What physical and chemical processes are not captured well by available models? Is there an optimum grid resolution to capture all of the relevant physical and chemical processes that occur?

11. What are the important transport corridors for key chemical species and under what conditions is that transport important?

12. What are the relative roles of regional (North American) sources and long range transport (from East Asia) on aerosol forcing over California?

Along with recent efforts to address climate change, ARB is contributing its expertise in air pollution studies with decades of baseline air quality data, an on-going atmospheric monitoring capacity and existing research capabilities. NOAA brings its ability to rapidly study the atmosphere over large areas of ocean and land by employing large, richly instrumented, long-range aircraft, a fully capable oceanographic vessel and its experienced scientists.

Started in early May continuing through most of June, the project involves four airplanes, an ocean-going research ship, two land-based air monitoring super sites and more than 150 scientists. The project is employing:

• Four aircraft: WP-3D, Twin Otter and CIRPAS’ Twin Otter from NOAA, and a King Air from NASA
• A research vessel (NOAA’s Atlantis)
• Two ground air monitoring super sites: Caltech, with more than 40 investigators, will focus on organic or carboneous PM and nighttime chemistry.
• Arvin (Kern County), with 18 investigators, will provide a comprehensive suite of chemical measurements that will significantly improve the understanding of ozone and PM formation of in the San Joaquin Valley.

NOAA’s contribution of hardware and expertise is estimated at $15 million. California is contributing $5 million, as well as the expertise of their meteorological, modeling, monitoring and research staff. Researchers from all over the United States and Europe will also be on the teams collecting data.

The data collected will give scientists a better understanding of atmospheric-chemical transformations, climate processes, transport and meteorology. This will improve ARB’s methodologies for measuring greenhouse gases, traditional air pollutants and their precursors.

In addition, the study will improve ARB’s understanding of the atmospheric formation of ground-level ozone and PM that will improve air-quality models which in turn enables ARB to develop more effective control strategies.

Other specific benefits stemming from CalNex California will include:

• Refining methods for determining greenhouse gas and air-pollutant emissions. The teams will look to interpret ambient CO₂ measurements to provide feedback to the emissions inventory. They are able to avoid complications from background concentrations, multiplicity of sources and the absorption and release of CO₂ by the biosphere. The use of aircrafts’ spatial coverage and resolution will provide valuable information on CO₂ and other gases. Such data can be used to analyze emission trends, and develop methods to evaluate the effectiveness and potential of carbon sequestration, including natural, agricultural and forestry methods.

• Improvement of Air Quality Modeling. ARB depends on air quality models to prepare strategies for reducing air pollution and complying with federal clean air standards. The State Implementation Plan is the compendium of strategies that must be submitted to the federal government. CalNex can provide key data that will benefit the state’s air quality models with three-dimensional, complementary measurements collected by the aircrafts, ship and ground sites. Each aircraft is not only a mobile monitoring platform and vertical profiler, but also a “supersite” with an extensive complement of technology that can characterize collected gas and particle chemicals. The quality of instrumentation and the advantages of range, speed and vertical profiling that an aircraft can accommodate will provide highly valuable information to refine air-quality models and ensure that upcoming SIPs are based on the best science.

Resources

• CalNex 2010 - An Air Quality and Climate Change Field Study in California in 2010