1997 Southern California Ozone Study - NARSTO
Air Quality Sampling Aloft

This page updated February 6, 2006.


Air Quality Sampling Aloft

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Air Quality Sampling Aloft During SCOS97 - NARSTO

Characteristically, air pollution monitoring sites are located in urban areas where the health impacts of air pollution are of greatest concern. However, to understand the formation and distribution of ozone on a regional scale, additional monitoring is needed in areas where the recirculation and transport of ozone and ozone precursors may occur. This is especially important aloft, where the formation and distribution of ozone concentrations are understood inadequately. To better understand the formation and distribution of ozone, the 1997 Southern California Ozone Study conducted in coordination with the North American Research Strategy for Tropospheric Ozone (SCOS97-NARSTO) provided for air quality measurements aloft. These non-routine measurements during the Intensive Operational Periods (IOPs) of SCOS97-NARSTO included a variety of monitoring platforms: six aircraft, seven ozonesonde release sites and two lidar sites. Click here for more information about the sampling aloft platforms. These additional measurements provide critical detailed information pertinent to running and validating the output of air quality models which can have difficulty simulating the observed vertical distributions of pollutants. Because previous modeling efforts underestimated the amount of ozone in the central basin where ozone concentrations tend to be highest, the El Monte Airport, near the center of the basin, was established as the hub site for enhanced monitoring aloft.
Previous studies also demonstrated the complexity of air circulation offshore southern California and the importance of adequately characterizing the meteorological and air quality conditions there. During the IOPs, 1-2 instrumented aircraft provided additional, detailed data on conditions over the Southern California Bight.
The primary objective of the ozone lidar at El Monte Airport was to provide a continuous record during IOPs of the development of ozone concentrations in this area of typically high ozone concentrations. Ozone concentrations were monitored at ground level with a traditional ozone monitor and up to two kilometers with the differential absorption lidar (DIAL). Click here for a sample of how the vertical profile of ozone concentrations changed during a day of ozone concentrations. The precision of the lidar measurements decrease with altitude. Click here for an estimate of the precision of the lidar's ozone measurements. This lidar has a larger range than other lidars (generally from 500 - 1,500 meters) because the laser energy is allocated among multiple parallel beams. The lidar also has a two-dimensional scanning capability in a vertical plane (NW to SE, perpendicular to the typical airflow in the region). These lidar data will be useful (particularly with data from the collocated meteorological remote sensing system) for: 1) better understanding the dynamics of ozone formation in this area, 2) validating the performance aloft of modeling exercises, and 3) better quantifying ozone fluxes in the San Gabriel Valley.
With ozone concentrations in the SoCAB frequently violating the state and national ambient air quality standards and air typically flowing out of the SoCAB into neighboring air basins, quantification of ozone transport is a major concern. One of the major routes for airflow into the Mojave Desert is through Cajon Pass. Another lidar was positioned north of the Cajon Pass for a month (August 23 - September 19). This lidar can measure water vapor, temperature, and aerosol scatter in addition to ozone. Click here for sample vertical profiles or here for a sample time-height profile for ozone. This lidar, because of its meteorological and ozone applications, will prove useful in understanding the meteorological dynamics influencing ozone
Seven sites for releasing ozonesondes were established for the field study. In principle, these sites collected data on the vertical distribution of oxidant concentrations around the hub site at El Monte AP. Ozonesondes were released four times per day during IOPs. The release times were nominally 0200, 0800, 1400 and 2000 Pacific Daylight Time. The ozonesonde release sites were Point Mugu in Ventura County, California State University, Northridge (San Fernando Valley) and the University of Southern California in Los Angeles County, Anaheim in Orange County, Pomona near the county line between Los Angeles and San Bernardino, the University of California, Riverside in Riverside County and Valley Center in San Diego
Instrumented aircraft provided additional, detailed data on conditions aloft in the study domain, during IOPs and on some occasions the day before or after an IOP. Five aircraft were dedicated to the ozone study. Four of the aircraft collected samples of speciated volatile organic compounds (VOC) and carbonyls and also monitored total reactive nitrogen species (NOY). Click here for a listing of the aircraft measurement instrumentation. In general, these planes each made a morning and an afternoon flight. Click here to see the typical flight paths. Downward spirals were generally flown for characterizing the vertical distribution of pollutants. Click here to see a table listing the locations of aircraft spirals during the study. Please note that spirals were not conducted at all these locations on every day. A sixth aircraft was dedicated to the aerosol component of SCOS97-NARSTO and flew on many days between late August and late September to characterize the three-dimensional distribution of aerosols.
The aircraft flights provided critical measurements of conditions aloft where carryover and transport of polluted air masses could significantly influence the performance of the model and influence pollutant concentrations at ground level. It is important that the air quality model application accurately simulate the ground level observations for the correct reasons. The over water flights are particularly critical to the success of the modeling exercises because they provide the upwind boundary conditions (i.e., the air quality flowing into the modeling domain) and initial conditions in this large, poorly understood region. Various measurements and modeling studies have indicated that air circulation over Southern California and the Southern California Bight is complex and that evidence of anthropogenic activity can routinely be found far offshore the South Coast Air Basin.
The primary objective of the San Diego - Navajo was to make the ozone, NOY and VOC measurements on the western boundary of the modeling domain and offshore. This aircraft was based out of Montgomery Field in San Diego County. The almost four-hour flight would take generally take a clockwise elliptical route around the islands (i.e., south of San Clemente Island, south and west of San Nicolas Island, west, north and east of the Channel Islands (San Miguel, Santa Rosa, Santa Cruz and Anacapa Islands) and east of Santa Catalina Island) before returning to Montgomery Field. Modifications to the flight plan were made during the study to reduce the duration of the flight to ensure adequate fuel reserves and to avoid military airspace when training areas were "hot." Spirals were made near San Clemente Island, San Nicolas Island, Point Conception and Santa Catalina Island. VOC samples were collected below 500 feet MSL near San Clemente Island, below 500 feet and between 4,500 and 6,000 feet near San Nicolas Island, between 4,500 and 6,000 feet near San Miguel Island, and below 500 feet near Santa Catalina Island.
The primary objective of the STI-Aztec was to provide data on conditions in the northern portion of the study domain. These data are particularly important for establishing the initial conditions but also for characterizing boundary conditions under scenarios such as the Type 5 Episode where the northern boundary becomes the upwind boundary for the study domain. Typically, the Aztec would fly the northern leg of its flight plan (i.e., through the Mojave Desert) in the morning of the first day of an IOP (to characterize initial conditions) and return to its base airport in Camarillo in the afternoon by flying through the SoCAB (to characterize the vertical structure of ozone and oxides of nitrogen during the build-up day of the ozone episode). On the remaining days of an IOP, the flight path was reversed with a flight through the SoCAB in the morning (to identify carryover from the previous day) and a flight through the Mojave Desert in the afternoon (to identify any afternoon transport). Spirals (generally over airports) to clearly characterize the vertical distribution of pollutants were made (depending on the flight path) at Camarillo and Simi Valley in Ventura County; Rosamond, Hesperia and Yucca Valley in the Mojave Desert; Santa Monica Bay (near Malibu), VanNuys and El Monte in Los Angeles County; Ontario and Rialto in San Bernardino County; and Banning and Riverside in Riverside County. The Aztec generally collected a total of eight VOC and carbonyl samples each day of an IOP. The Aztec also served as a backup for the Navajo on the western boundary route.
The primary objective of the UCD-Cessna 182 operating in the SoCAB was to provide data on conditions in the central portion of the basin. Two to three flights were flown per day from the base airport at El Monte to Burbank Airport to Cable Airport (near Fontana in San Bernardino County), to Fullerton Airport (in Orange County), and back to El Monte Airport with, spirals being flown at each location. Additional spirals were flown near Pasadena and Azusa. The two spirals per flight at the El Monte AP also provided "checks" on the performance of the ozone lidar located there. Two VOC and carbonyl samples were collected per flight: one at El Monte AP between 1,600 and 2,600 feet and one at Azusa, also between 1,600 and 2,600 feet.
The primary objective of the SD-Cessna 182 operating in San Diego County was to provide data on conditions in the southern portion of the study area and to identify any overland transport of ozone into San Diego County. The typical flight plan for this aircraft took it from its base at Montgomery Field to Alpine to Valley Center to Temecula, to Pine Mountain Camp to Warner Springs to Lake Henshaw to offshore of Oceanside to offshore Encinitas to Lake Hodges to Gillespie Field to Montgomery Field. Spirals were performed at Alpine, Valley Center, Temecula (French Valley AP), Pine Mountain Camp, Warner Springs and Oceanside. Four VOC and thee carbonyl samples were generally collected per flight.
The primary objective of the USN-Partnavia was to map the three-dimensional distribution of ozone concentrations and the horizontal extent of any ozone layers encountered off the coast of Ventura and Los Angeles Counties. This aircraft was based at the Oxnard AP. The Partnavia mapped ozone concentrations over the ocean west and southwest of Santa Monica Bay.
The primary objective of the CIRPAS-Pelican was to map the three-dimensional distribution of aerosols in the SoCAB. This aircraft was also based at the El Monte AP. The plane contained three different types of aerosol analyzers and could generate detailed information on the size distributions of aerosols (between 0.005 and 47 microns).
Sample Vertical Profiles of Ozone Concentrations on September 28, 1997
Weak Santa Ana winds resulted in an atypical distribution of ozone concentrations on September 28. Ozone concentrations were lowest in the extreme eastern portion of the Los Angeles area but high concentrations were observed elsewhere, even as far west as San Nicolas Island. Click here to see the vertical profiles of ozone concentrations observed on September 28, 1997: Planes and Lidar or Ozonesondes.
Intercomparisons of air quality aloft measurements were made during SCOS97-NARSTO to evaluate the comparability of data from different platforms. The purpose of the intercomparisons was to identify and quantify biases within (e.g., hysteresis in aircraft measurements) and between platforms. The University of California (Davis) aircraft served as a common link in the intercomparisons. The intercomparisons were scheduled so as not to interfere with activities during IOPs. Consequently, ozone concentrations during the intercomparisons generally were not as high. Ad-hoc intercomparisons occasionally occurred during the IOPs when an aircraft was near another platform at approximately the same time as other measurements were being made. Most of the ad-hoc intercomparisons occurred at El Monte Airport because it was the hub site for the ozone aloft measurements during IOPs (nearly continuous measurements by NOAA's lidar, two spirals per flight of the UCD aircraft and an occasional spiral by the STI aircraft).
The intercomparisons will be posted as the they become available. Please check back soon to view them!

SCOS97 Data Summary
SCOS97-NARSTO Information Contact