1997 Southern California Ozone Study - NARSTO Background

This page last reviewed June 10, 2000

The 1997 Southern California Ozone Study Counts Down to June 16
In order to develop databases to support detailed photochemical modeling and analysis for a better understanding of 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 are co-sponsoring the 1997 Southern California Ozone Study - North American Research Strategy for Tropospheric Ozone (SCOS97 - NARSTO).
(NARSTO is a composite organization whose membership spans government, the utilities, industry and academia throughout Canada, Mexico and the United States. Its primary mission is to coordinate and enhance scientific research and assessment of tropospheric ozone behavior, with the central programmatic goal of determining workable, efficient and effective strategies for local and regional ozone control.) The SCOS97 - NARSTO meteorological network and most of the air quality network will collect data from June 16 to October 15, 1997. During intensive operational periods (15 days planned), emission data and additional meteorological and air quality data will be captured for five different types of multi-day ozone episodes of interest to the sponsors.
Within the ARB, SCOS97 - NARSTO is a cooperative effort between the Research Division (management, design, contracts, data management), the Technical Support Division (management, design, emission inventory, data management) and the Monitoring and Laboratory Division (quality assurance, radar wind profiler operations).
Remote Sensing of Meteorology for SCOS97 - NARSTO
The large study domain (80,000 mi2) of SCOS97 - NARSTO, which includes an extensive land-sea interface and complex topography, requires an extensive network of upper-air monitoring sites. The SCOS97 - NARSTO will use remote sensing methods -- radar wind profilers equipped with radar-acoustic sounding systems (RWP / RASS) -- to continuously observe meteorological conditions above the surface. The RWP measures the average wind speed and direction for 60-meter layers with a range from about 100 to 1,500 meters above ground level. The RASS measures the air density and reports it as virtual temperature, with about the same vertical resolution and range. (Virtual temperature is a variable to express the combined effects of temperature and humidity on the density of air in order to evaluate at what levels in the atmosphere density stratification may suppress or enhance vertical mixing.) Two contractors, the National Oceanic and Atmospheric Administration (NOAA) and Radian, are establishing a total of 18 new RWP / RASS sites for SCOS97 - NARSTO. These will upplement eight permanent RWP / RASS stations in Southern California, operated by the ARB, air quality districts and military bases. Two of the RWP / RASS sites operated by NOAA are being sited along the California - Mexico to help study cross-border transport.
During the SCOS97 - NARSTO intensive operational periods, military bases, the National Weather Service and ARB staff will provide upper-air observations using balloon-borne rawinsondes (measuring wind speed and direction, temperature, humidity and pressure) at 12 sites. These observations will be used with the meteorological model (MM5) developed at Pennsylvania State University to characterize airflow in Southern California and provide meteorological inputs for air quality modeling.
Air Quality Aloft Measurements Planned for SCOS97 - NARSTO
A deficiency in previous field studies of air quality in Southern California has been the limited measurements of meteorology and air quality at altitudes above the levels monitored by traditional ground-based in-situ instruments. On the 15 intensive operational periods during the study, enhanced monitoring of air quality aloft will occur. Measurements aloft will be made by aircraft (four dedicated and two ancillary), an ozone lidar, balloon-borne ozonesondes (four releases per day from seven sites). Ozone concentration measurements are the common theme for all of the measurement platforms but the dedicated aircraft will also measure oxides of nitrogen and take samples for later analysis of speciated hydrocarbons and carbonyl compounds. The lidar will also provide vertical profiles of aerosol scattering. These data will be used to provide boundary and initial conditions for photochemical models. The data will also be used to validate the performance of the models and in analyses to refine our understanding of the complex ozone processes (formation and transport) in Southern California.
Hydrocarbon and Related Sampling During SCOS97 - NARSTO
In addition to the required speciated hydrocarbon sampling performed by the districts as part of their photochemical assessment monitoring stations (PAMS), several special studies are planned for SCOS97 - NARSTO. Additional sampling of speciated hydrocarbons and carbonyl compounds will be performed at San Nicolas Island (background), Downtown Los Angeles (source) and Azusa (receptor) during the 15 days of intensive operations. The U.S. EPA has provided funding to measure speciated hydrocarbons at two additional background sites -- Rosarito Beach and SE Mexicali -- to assist in determining Mexico's possible contribution to pollution concentrations in California. Aircraft sampling will also be performed to determine the concentrations aloft. The U.S. EPA and their contractor will monitor hydrocarbons on a continuous (hourly) basis during the month of September in Azusa. The species measured will include carbonyl compounds, biogenic hydrocarbons and chlorinated hydrocarbons which are not routinely monitored by the PAMS program. Several other groups are measuring the halogenated hydrocarbons perchloroethylene and methyl chloroform. These are "tracers of opportunity" that can be used to tag emissions from the South Coast Air Basin. Portland State University (PSU) will measure hydroxyl and hydroperoxy radicals (important intermediates in hydrocarbon reactions and ozone formation) at UC Riverside.
These data will be used to provide boundary and initial conditions for photochemical (emission-based) models. The data will also be used to improve our understanding of emissions and ozone formation processes in Southern California through the use of observation-based models. The results of the PSU study will assist in validating model results of the radical species and help us better understand their critical role in ozone generation.
SCOS97 - NARSTO Total Reactive Nitrogen Species Measurements
Staff from the Research, Technical Support, and Monitoring and Laboratory Divisions and Mr. Dennis Fitz (UC Riverside) held a series of discussions from December 1996 to March 1997 concerning measurement of total reactive nitrogen species (NOY) during SCOS97 - NARSTO. Candidate measurement instruments were challenged at the UC Riverside environmental chamber with known concentrations of NO, NO2, nitric acid, and PAN. The Thermo Environment's TECO 42CY instrument measures NOY and NO using chemiluminescence and has proven to be an extremely stable instrument with limits of detection as low as 50 ppt. A network of 12 samplers will be deployed at background, South Coast Air Basin, outflow and receptor sites. In addition, three of the aircraft will contain the same type of NOY monitor. During the 15 intensive operational periods of the study, spectroscopic and other research-grade instrumentation will be used to measure NO2, nitric acid and PAN to provide a check of the Teco 42CY. Most of the samplers will be located at PAMS sites to better achieve the same goals described in the preceding highlight on hydrocarbon sampling.
Biogenic Hydrocarbon Measurements During SCOS97 - NARSTO
During SCOS97 - NARSTO, several investigators hope to ground-truth the biogenic hydrocarbon (BHC) contribution to ozone formation in the South Coast Air Basin and to verify high isoprene emission flux estimates in the Ojai area. Professor Janet Arey of UC Riverside will sample for isoprene, monoterpenes and possibly methylvinylketone (MVK) during afternoon upslope flows at a high elevation site in the San Gabriel Mountains. Isoprene is so reactive it can disappear on the order of minutes, preventing detection of significant quantities; MVK is a slow-reacting byproduct of isoprene oxidation. Professor Arey and collaborators at UCLA plan to collect samples downwind of a large oak stand in the Ojai area, as oaks are sources of large emissions of isoprene. In addition, UC Riverside will measure methylnitronaphthalenes to infer 12-hour average nitrate radical concentrations, the dominant night-time sink of BHC. Several other groups will make surface and aircraft measurements of isoprene and monoterpene for later comparison with UC Riverside. In a separate experiment, the U.S. EPA will perform radiocarbon dating of collected ambient hydrocarbons to determine the proportion of "modern carbon" as a tracer of biogenic hydrocarbons.
SCOS97 - NARSTO Aerosol and UV Radiation Experiments
In addition to the primary mission of characterizing ozone formation processes, the SCOS97 - NARSTO program will conduct coordinated studies to look at other aspects of atmospheric chemistry. Two of particular interest are the aerosol program and a study of solar ultraviolet radiation.
The aerosol study will employ advanced instruments recently developed at UC Riverside (under ARB sponsorship) to determine the size and composition of individual particles in the air, as well as more conventional samples collected both on the ground (funded by the Coordinating Research Council and the National Renewable Energy Laboratory) and from an airplane. This study should help us to understand the origins and processing of "primary" particles, as well as shed light on the chemical processes that convert some of the gaseous pollutants in the air into "secondary" particles. From this we should gain a better understanding of how ozone control programs may also reduce particle concentrations in the South Coast Air Basin.
The solar ultraviolet radiation study will consist of short-term experiments conducted at UC Riverside (high atmospheric aerosol loading) and Mt. Wilson (generally above the polluted layer) in June and September. The two studies will measure how ultraviolet radiation, which is a driving force behind ozone formation, is absorbed and scattered in the lower atmosphere. We anticipate that these measurements will help us to better relate the photochemistry we observe in laboratory experiments to what is really occurring in the atmosphere; eventually, we expect to be able to use these findings, coupled with continuous solar radiation measurements taken at several SCOS97 - NARSTO monitoring sites, to improve our atmospheric photochemical simulations to be even more tightly tied to fundamental physical and chemical processes.