Atmospheric Field Studies

This page last reviewed March 11, 2015

monitoring platform collage

In compliance with U.S. Environmental Protection Agency (U.S. EPA) regulations and guidelines, the California Air Resources Board (ARB) and local air pollution control districts routinely collect ambient air quality data for the State of California, act to ensure the quality of these data, and make them available to the public.These data are used to examine temporal and spatial variations of ambient air pollutants, to assess compliance with ambient air quality standards, and to evaluate air quality model results that are used to develop the State Implementation Plans for achieving healthful air quality for the public. However, this routine air monitoring network is limited in the number of pollutants and the spatial extent (particularly in the vertical dimension) that it can characterize. Thus, the air quality community also conducts field studies on occasion to supplement the routine meteorological and air quality measurements and to improve its understanding of atmospheric processes.The Legislature of the State of California has endorsed such research (via Sections 39700 - 39706 of the California Health & Safety Code) as a critical component of identifying sources and types of pollutants and developing air pollutions control measures.

The pictures above illustrate some of the various platforms (e.g., in-situ: planes, ships, cars, balloons; remote sensing: lidars, satellites) used to measure air quality and meteorological parameters in our atmosphere. This linked Excel file is a table identifying many of the various field studies and measurement projects that the Research Division has sponsored in whole or in part during the last quarter century.

Listed below are some atmospheric research studies conducted since 1985 that were supported, in whole or part, by the Research Division of ARB to better characterize our knowledge and modeling of atmospheric processes (involving emissions, meteorology, air quality, climate, exposure). The list is arranged in chronological order with the current and longest-running projects appearing first.

Mobile Monitoring Platform (2003 – present)

Several Toyota RAV 4 Electric Vehicles (EV) have been outfitted with an array of air monitoring instruments to measure greenhouse gases (GHG) and toxic air pollutants important to exposure and community health. Projects are currently underway to investigate pollutant levels near and on several freeways in the Los Angeles area, greenhouse gas emissions from poorly characterized sources, the effect of high emitting vehicles on short-term exposure, and community health monitoring.

Much of the monitoring equipment has never been used in a mobile manner prior to these projects. Among the equipment in the EVs are NOx and CO analyzers, an N2O and CO2 analyzer, a nephelometer, an aethalometer, PM10 and PM2.5 monitors, an ultrafine particle counter, and an ultrafine particle size classifier. These electric vehicles are used for this type of research because they have adequate interior volume for the monitoring equipment, have no emissions of their own to contaminate the samples being collected, and have the mobility to safely go where emissions are released or where people are routinely exposed to pollutants. For more information, please contact Kathleen Kozawa at (916) 323-2229.

Mobile Measurement of Greenhouse Gas Emissions (2009 – present)

Field research efforts to verify the California greenhouse gas (GHG) emissions inventory, as instructed by Assembly Bill 32, are currently underway using mobile measurement platforms. Two electric vehicles outfitted with an extensive suite of analytical instrumentation conduct data collection experiments using several sampling methodologies to assess the GHG emissions from a variety of source categories. Measurements include GHG mixing ratios (CH4, N2O, CO2 and CO), particulate concentration metrics (PM2.5 mass, PM1.0 number, and Black Carbon), and meteorology metrics (wind speed, wind direction, temperature and relative humidity). Active research collaborations with industry and academia are fostered where available, and collocated data collection events are pursued to enhance the power of each data set and to provide additional quality assurance via intercomparison of data collection methods. These field studies serve to develop and refine measurement protocols to accurately ascertain the GHG source emissions such that the existing emissions inventory values can be evaluated and uncertainty in future values can be reduced. For more information, please contact Abhilash Vijayan at (916) 324-0621.

Greenhouse Gas Monitoring Network (2010 – present)

The objective of this project is to establish a greenhouse gas (GHG) monitoring network in California with state-of-the-art analyzers at air quality monitoring stations that complement the existing GHG measurement sites in California. Measurements are needed especially in the San Joaquin and Sacramento Valleys and southern California, where there are many GHG emission sources, such as landfills, oil and gas extraction facilities, natural gas systems, rice paddies, dairies, waste water treatment facilities, and feed lots. Seven GHG monitoring stations have been established at locations where they represent the regional atmospheric compositions: two in Los Angeles, three in the San Joaquin Valley and two in the Sacramento Valley. Starting in May 2010, this network has provided high quality measurements of methane (CH4) concentrations. The Research Division’s pilot CH4 monitoring network was the first of its kind deployed at the regional level and with a monitoring network sufficiently dense to identify emission sources and to “true-up” the inventory of anthropogenic CH4 emissions. The methane monitoring has now been expanded to include other GHGs (CO2, N2O, and other gases with high global warming potentials). In the near future, ARB’s Monitoring & Laboratory Division plans to measure black carbon particulate matter (BC) at these sites as well. Over time, the GHG monitoring network will provide the critical data necessary to evaluate the effectiveness of California’s efforts to reduce pollutants that contribute to climate change. For more information, contact Ying Hsu at (916) 323-5774.

Enhanced Sulfur Study of Southern California (2012-2013)

As a component of ambient particulate matter, particulate sulfate is a pollutant of concern for ARB and local districts. Questions about the sources and formation mechanism of particulate sulfate (sulfate) in the South Coast Air Basin (SoCAB) have been investigated beginning in the 1970s. Recognizing the need to reduce sulfur pollution, ARB and the local districts have regulated the sulfur content of fuels and stationary combustion sources, resulting in a 74% reduction in SOx emissions from 1990 to 2012. But sulfate still accounts for ~15% of the annual PM2.5 mass at selected sites in the SoCAB and SOx emissions are expected to start increasing as population and economic growth overcome the effects of regulations sometime after 2015. The first step in identifying additional potential reductions is to reexamine the sources of sulfate in SoCAB with particular attention to sources and processes not currently in ARB’s inventory, such as oceanic emissions of dimethyl sulfide. For these reasons, the Monitoring and Laboratory and Research Divisions conducted the Enhanced Sulfur Study of Southern California [ESSSC] which collected continuous sulfate data at six sites - four SCAQMD monitoring sites and two new sites on Santa Catalina Island, from the spring of 2012 to the spring of 2013. Data analysis by ARB staff is underway. For more information, contact Eileen McCauley at (916) 323-1534.

Research in California at the Nexus of Air Quality and Global Climate Change (CalNex 2010)

CalNex 2010 was a major climate and air quality study in California jointly conducted by the National Oceanic and Atmospheric Administration (NOAA) and ARB, with the participation of numerous academic researchers from around the world measuring a wide variety of air quality parameters for 4 to 6 weeks. Additional material, including data, regarding the CalNex field study are accessible at NOAA. Various aspects of the field study began in May and continued into July of 2010. NOAA’s deployment of two aircraft in the State and the establishment of two supersites (Bakersfield and Pasadena) generated a dataset of unprecedented chemical completeness, spatial extent and temporal resolution. The presence of the research vessel Atlantis provided data about the emissions and impacts of shipping off California’s coast. The study provided insights and answers to important scientific questions about emissions, chemical transformations, climate processes, transport, and meteorology in California. The air quality and meteorological data collected during CalNex will improve ARB’s emission inventories of greenhouse gases, traditional air pollutants and precursors. In addition, the study data will inform ARB’s air quality models used in SIP development and our understanding of the atmospheric formation of ozone and PM. A synthesis report summarizes the main findings for policy-makers. 

A couple of additional field studies overlapped with CalNex 2010 and received administrative support from ARB. The Carbonaceous Aerosols and Radiative Effects Study (CARES) was sponsored by the U.S. Department of Energy. CARES investigated the formation of secondary aerosols downwind of Sacramento, CA. The California-Mexico Border Study (Cal-Mex 2010) investigated ozone formation and transport near the international border. For more information, contact Eileen McCauley at (916) 323‑1534.

Condensation Particle Count Study (2007-09)

This 3-year study was conducted by the University of Southern California and sought to accomplish several specific objectives via three deployments of a network of condensation particle counters (CPCs). The first deployment featured about a dozen CPCs within a significant source region associated with the movement of goods through the Los Angeles/Long Beach ports complex. This phase of the study was conducted in conjunction with the Harbor Communities Monitoring Study and investigated the fine-scale spatial and temporal variability of ambient particle number concentrations (PNC) within communities near the ports (e.g., San Pedro, Wilmington, Long Beach). The second phase of the study was conducted in the greater Riverside area to investigate the spatial and temporal variability of ambient PNC within communities that not only emit their own pollution but are impacted by emissions from upwind areas (i.e., local vs. regional contributions to PNC). The third phase of the study was conducted near two busy freeways in the Los Angeles area to investigate the effects of freeway sound walls on particle number and size distribution, as well as CO, NO2 and BC concentrations, in adjacent neighborhoods. For more information, contact Ash Lashgari at 916-323-1533.

Arctic Research in the Composition of the Troposphere from Aircraft and Satellites – California phase (ARCTAS-CA; 2008)

The National Aeronautics and Space Administration (NASA) collaborated with ARB on a brief study of atmospheric conditions aloft in 2008. NASA flew its DC-8 research aircraft, equipped with a full suite of monitoring instruments. The objective was to investigate the emission of air quality pollutants, greenhouse gases, and aerosols with extensive low altitude sampling of emissions across southern California, the Central Valley, offshore shipping lanes, and, serendipitously, numerous wild fires. The measurements provided detailed characterization of aerosols, ozone precursors, and secondary products for evaluating the performance of air quality models. The aircraft also flew over the Pacific Ocean, well off-shore of California, to provide boundary conditions for ARB to use in regional air quality models and testing the accuracy of global models for providing boundary conditions. The measurements also were useful for validating satellite measurements (e.g., OMI, TES, MODIS, MISR) and the potential use of their remotely sensed data for surface air quality applications. For more information, contact Eileen McCauley at (916) 323-1534.

Harbor Communities Monitoring Study (HCMS; 2007)

The Harbor Communities Monitoring Study (HCMS) was conducted to characterize air quality in the communities of the greater Wilmington area, located north of San Pedro Harbor. The air pollution measurement phase occurred during 2007. The primary goal of this study is to characterize the spatial variations in air quality in this area with various large emission sources. The measurement program featured non-traditional monitoring tools to cost-effectively characterize pollutant concentrations in the area and to identify locales where pollutant concentrations are high. The measurements consisted of three types of air pollution sampling: a network of passive samplers, a mobile monitoring platform, and a network of particle counters (see Condensation Particle Count Study above). The sampling program helped to characterize the temporal and spatial variations of air pollution in the study region. For more information, contact Ash Lashgari

Children’s Health Study (CHS; 1993-2004)

The Children's Health Study is a large, long-term, study of the effects of chronic air pollution exposures on the health of children living in Southern California. Children may be more strongly affected by air pollution because their lungs and their bodies are still developing. Children are also exposed to more air pollution than adults since they breathe faster and spend more time outdoors in strenuous activities. About 5500 children in twelve communities were enrolled in the study; two-thirds of them were enrolled as fourth-graders. Data on the children's health, their exposures to air pollution, and many factors that affected their responses to air pollution were gathered annually until they graduated from high school.

The Children's Health Study Final Report is available here and represents an extensive compilation of more than 10 years of community ambient air pollution measures and health outcomes related to lung function growth, asthma, bronchitis, and acute respiratory illnesses. Although the ARB funding support for the health portion of the study has concluded, the investigators have received support from the National Institute of Environmental Health Sciences to continue the program. For more information, contact Barbara Weller at (916) 324-4816.

Lake Tahoe Atmospheric Deposition Study (LTADS; 2003)

Between the mid-1960s and the mid-1990s, the water clarity of Lake Tahoe decreased from 100 feet to 65 feet. To address this deteriorating environmental quality indicator, California's Lahontan Regional Water Quality Board (LRWQCB) and the Nevada Division of Environmental Protection (NDEP) developed the Lake Tahoe Nutrient and Sediment Total Maximum Daily Load (TMDL). A TMDL is a water quality restoration plan designed to determine the ability of a body of water to accept contaminants without resulting in a reduction in water quality. Contaminants adversely affecting water clarity enter the lake via runoff containing sediments and nutrients, seepage of groundwater containing nutrients, shoreline erosion and direct atmospheric deposition. To update estimates of the impact of atmospheric deposition to the Lake, the ARB conducted a comprehensive field study. The objective of LTADS was to better quantify the atmospheric deposition of nutrients and particulate matter directly to Lake Tahoe. The study also provided insights into the relative contribution of local and regional sources of nutrients and PM to the declining water clarity of Lake Tahoe. For more information, contact Ash Lashgari at 916-323-1533

Central California Ozone Study (CCOS; 2000)

The Central California Ozone Study (CCOS) consisted of field measurements, data analysis, emission inventory development, and modeling. The field measurement program occurred during the summer of 2000. Emission inventory development, data analysis and modeling were on-going projects over many years (2000-2011). CARB and local air pollution control districts used the results of CCOS to prepare the demonstration of attainment for the ozone standard for non-attainment areas in central California. For more information, contact John DaMassa at (916) 324-7167.

California Regional Particulate Air Quality Study (CRPAQS; 1999-2001)

The California Regional PM10/PM2.5 Air Quality Study ( CRPAQS) was a comprehensive public/private sector collaborative investigation to provide an improved understanding of particulate matter and visibility in central California and to provide decision-makers with the tools needed to identify equitable and efficient control methods. The study evaluated both particulate matter smaller than 10 micrometers in diameter (PM10) and particulate matter smaller than 2.5 micrometers (PM2.5). Ambient air quality standards for both of these pollutants are consistently exceeded in central California, compromising the health of more than 10 million people. Excess particulate matter also reduces visibility, affects crop yields, causes materials damage, and adversely impacts the overall quality of life. The field study was designed to address annual particulate levels as well as fall and winter episodic conditions. Data were collected for 14 months (December 1999 through February 2001) throughout the San Joaquin Valley (SJV) and surrounding regions. For more information, contact John DaMassa at (916) 324-7167.

California Acid Deposition Monitoring Program (CADMP; 1988-97)

Scientific evidence in other parts of the world has shown that atmospheric deposition of sulfur and nitrogen compounds can cause harm to the environment and, thus, may present a threat to California's ecosystems and the health of its citizens. To adequately address this concern, the causes and effects of acid deposition in California were studied in two comprehensive State-funded monitoring and research programs. The California Legislature enacted the Kapiloff Acid Deposition Program (KADP) and the Atmospheric Acidity Protection Program (AAPP). These studies examined the atmospheric processes associated with acid deposition and its effects on human health, aquatic ecosystems, forest ecosystems, agricultural crops, and man-made materials. Concentrations of acidic air pollutants in precipitation, fog, and dry-deposited particles and gases were measured in support of the KADP and AAPP by the Air Resources Board's California Acid Deposition Monitoring Program (CADMP). The monitoring network associated with dry deposition consisted of ten sites representing various exposures throughout the State - from Gasquet in northern California to Long Beach in southern California. The CADMP monitoring was terminated in September 1995. For more information, contact Nehzat Motallebi at (916) 324-1744.

Southern California Ozone Study (SCOS97-NARSTO; 1997)

This major field study collected extensive data in southern California in 1997 to support detailed photochemical modeling and data analysis. The objective was to better understand and document the processes involved in the formation of high ozone concentrations in the South Coast Air Basin and across the southern California region. The ARB, the Mojave Desert AQMD, the San Diego County APCD, the Santa Barbara County APCD, the South Coast AQMD, the Ventura County APCD, the U.S. EPA, and the U.S. Navy collaborated to-sponsor the 1997 Southern California Ozone Study - North American Research Strategy for Tropospheric Ozone (SCOS97 - NARSTO). The SCOS97 - NARSTO meteorological network and most of the air quality network collected data from June 16 to October 15, 1997. During intensive operational periods (5 multi-day campaigns), emissions data and additional meteorological and air quality data were captured for five different types of multi-day ozone episodes of interest to the sponsors. A compact disc (CD) of the meteorological and gaseous air quality data collected by the various study participants is available. For more information, contact Ash Lashgari at 916-323-1533

Ozone Transport Corridors Study (1995)

This monitoring program was conducted during the 1995 ozone season to examine the transport of ozone along two corridors out of the South Coast Air Basin (SoCAB): 1) into the Mojave Desert, and 2) offshore toward the San Diego Air Basin. Eight sites (continuously monitoring ozone, ambient temperature, wind speed and direction) were established and operated for a period of five months (June-October 1995) throughout southern California (7 sites at strategic locations in the Mojave Desert and 1 site at the airport on Santa Catalina Island). The island site and three sites on prominent peaks in the desert served as surrogates for continuous measurements of conditions aloft. The representativeness of measurements made at these “at altitude” sites was evaluated by comparisons with remote sensing instruments and aircraft soundings. These measurements, together with data from the long-term monitoring network and other supplementary sources, were analyzed to better characterize the frequency of transport from the SoCAB into the Mojave Desert and the relative contribution of local sources to ozone exceedances in the Desert. Specific investigations were pursued when the data were deemed worthy of closer examination (e.g., ozone exceedances at the Santa Catalina Island site). For more information, contact Ash Lashgari at 916-323-1533

Sierra Cooperative Ozone Impact Assessment Study (1990-94)

In the 1980s, studies conducted on pine trees in the Sierra Nevada found leaf injury characteristic of the damage caused by ozone. However, due to the lack of air quality data in forested regions of the State, a causal relationship to ozone exposure could not be established. In response to the need for air quality data, the Sierra Cooperative Ozone Impact Assessment Study (SCOIAS) was initiated in 1990 to measure ambient concentrations of ozone and a suite of meteorological parameters in mid-elevation conifer forests in the Sierra Nevada. The objective of this study was to determine the ozone exposures of ozone-sensitive pine tree species during the growing season (May through October). The SCOIAS consisted of a network of six monitoring stations in five national forests. The northernmost station was White Cloud in the Tahoe National Forest and the southernmost was Mountain Home in the Sequoia National Forest. Peak hourly average ozone concentrations were greater than 60 ppb at all sites in the network and frequently exceeded 80 ppb. These levels have been found to cause needle injury in laboratory studies and in forests in southern California. In future years, the risk to mid-elevation conifer forests in the Sierra Nevada from ozone may increase as a result of increased amounts of emissions generated from expanding urban centers in the Central Valley and foothills. For more information, contact Ash Lashgari at (916) 323-1506.

Los Angeles (Claremont) Free Radical Study (1993)

The hydroxyl free radical (OH) initiates and propagates atmospheric photochemical reactions that lead to the formation of ozone and essential components of particulate matter. In 1993, the Environmental Protection Agency funded the first use of a low-pressure, laser-induced fluorescence (LIF) spectroscopic device to directly measure free-radical concentrations in Claremont, California. There are very few other reliable methods for accurate and direct measurement of OH. Measurements of atmospheric chemicals involved in free-radical processes are also critical for improving OH estimates in photochemical models. Data from studies such as this one are important for providing information to support direct free-radical measurements and can also be used to determine changes that have occurred in the atmosphere downwind of Los Angeles. For more information, contact Ash Lashgari at (916) 323-1506.

Atmospheric Transport Assessment Study (1991 in NorCal; 1992 in SoCal)

NOAA's Environmental Technology Laboratory (ETL) used its boundary-layer 915-MHz radar wind profilers and supporting meteorological instrumentation to monitor and study major interbasin transport corridors for ozone (and its precursors) over two summer ozone seasons during 1991 and 1992. Wind profilers, some equipped with RASS temperature profiling, were deployed at twenty-five sites throughout California. The goal was to provide data necessary to meet ARB needs to assess transport of ozone and its precursors in a number of transport couples throughout the State using wind and mixed layer depth determinations from profilers. A data base and workstation were provided that would assist future modeling exercises and real-time data evaluation and transfer capabilities.

In the course of the study, NOAA discovered contamination of the wind data by migrating birds (nocturnal and seasonal) and found the effect to be significant along certain migratory paths in spring and early summer and again in late summer and early fall. In response to the seriousness of the problem, NOAA developed new editing methods to flag contaminated data after the fact and also developed new signal processing routines that eliminate a substantial fraction of the contamination in real-time. With the re-edited data, NOAA carried out a number of analyses of meteorological conditions associated with high- and low-ozone periods in selected areas. In addition, a series of short term supplemental measurement campaigns suggested that the dynamics of the diurnal, thermally-forced circulation along the major topographic boundaries of the Central Valley and the South Coast Basin play a significant role in the recirculation of pollutants in some cases and their transport into other air basins in other instances. Analysis of profiler data adjacent to Banning and Cajon Passes in southern California suggested that such passes can be easily monitored with wind profilers to determine the direction and depth of transport from one basin to another. For more information, contact Ash Lashgari at 916-323-1533

Walnut Grove Tower Study (1992, 2005 - present)

Ozone concentrations are routinely measured at more than 200 ground-level monitoring sites in California. However, surface measurements often are not representative of concentrations a few hundred feet higher. Photochemical models indicate that ground-level ozone concentrations are sensitive to the amount of pollution aloft, which may have persisted from the previous day or may have been transported from another area. Ozone concentrations aloft are generally only measured during special studies utilizing aircraft, lidars, or balloons. These methods provide limited temporal coverage and are resource-intensive. This study was conducted to determine whether ozone concentrations can be measured using conventional ozone monitors with long sampling lines attached to tall towers.

In this project, the investigators measured ozone concentrations during the summer of 1992 at a television transmission tower located in Walnut Grove, between Sacramento and Stockton. Sampling lines were run from the support building to the 30-foot, 400-foot, 800-foot, 1200-foot, and 1600-foot levels of the 2000-foot tower. Ozone concentrations were similar at all levels during the afternoon when vertical mixing of the air was greatest. During the night, however, concentrations were generally low below 400 feet but comparable to the daytime values at higher altitudes. In addition to collecting data with analyzers dedicated to each level, the study included an analyzer that sequentially sampled concentrations from each level of the tower. Ozone concentrations measured by the sequential analyzer compared well the data from the dedicated analyzers. This comparability of data by the two methods indicates potential opportunity for collecting ozone data at several levels with only one analyzer. The single analyzer approach would require fewer resources and provide more accurate data on the concentration differences between levels than would the dedicated analyzer approach. These real-time data above ground level are useful for making ozone air quality forecasts and agricultural burning decisions as well as occasionally evaluating the performance of air quality models.

The ARB and the Sacramento Metropolitan Air Quality Management District have contracted for ozone and meteorological measurements on the Walnut Grove Tower since 2005. These data can be accessed on the web. For more information, contact Ash Lashgari at 916-323-1533

If you have any questions or comments about the content of this Field Studies web page, please contact Ash Lashgari at 916-323-1533.

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