Study 153: Protocol for Analyzing Lompoc Weather Patterns

Bruce Johnson, Senior Environmental Research Scientist

California Department of Pesticide Regulation

Environmental Monitoring and Pest Management

Environmental Hazards Assessment Program

1020 N Street, Room 161

Sacramento, CA 95814-5624

October 1, 1996

  • Background
  • The use of pesticides in agricultural areas close to urban dwellings is controversial as urban residents have become more concerned about pesticides in the air, soil, and water, and about the effectiveness of regulatory restrictions in protecting citizens from pesticide exposure.

    Citizens in the city of Lompoc, Santa Barbara County, have brought their concerns about use of agricultural pesticides to the forefront. Since late 1993, the Santa Barbara County Agricultural Commissioner's Office has received written complaints from Lompoc residents about pesticide use near their town. They have attributed health problems to pesticide use and have expressed concern about exposure to agricultural chemicals which were being carried from fields as a result of local weather conditions. A constant concern raised by the community is that the local weather patterns (i.e., wind, fog, inversions) result in high exposure to pesticides. Although there is no well-defined health problem, and no evidence that specific pesticides are posing a risk to public health in the Lompoc area, the Department of Pesticide Regulation (DPR) is proposing a variety of approaches and activities in the agricultural/urban interface to promote reduced-risk pest management practices. We believe that the underlying factor for determining whether residents in Lompoc are highly exposed to pesticides is based more on the local weather pattern than particular pesticides being used. Therefore, an evaluation of the weather patterns in the Lompoc Valley needs to be done.

  • High pesticide concentrations in the air may result from two different kinds of processes: outgassing following application or direct spray drift occurring from aerial applications. From a technical perspective, these two processes are governed by different meteorological parameters.
  • High pesticide air concentrations from outgassing could result when either/or outgassing rates are high and meteorological conditions are stable. When meteorological conditions are stable, vertical mixing is reduced and plumes tend to remain cohesive, with high pesticide concentrations. During unstable meteorological conditions, vertical and lateral mixing reduce the concentration of pesticides within the downwind plume.
  • Another phenomenon which could contribute to high air concentrations is the presence of low altitude inversion layers. While it would be desirable to characterize the presence of low level inversion layers, the historical meteorological data does not contain the necessary information to support such a determination.
  • The second process, drift from spray, is thought to be minimized during wind speeds between 2-10 mph (U.S. EPA, 1995)
  • Purpose
  • It is the overall aim of this study to delineate time periods when conditions might favor high concentrations of pesticides from outgassing or when conditions might favor drift due to wind speeds being outside the 2-10 mph zone. The purpose is to determine whether meteorological conditions in Lompoc uniquely favor weather conditions which could result in higher than average air concentrations or drift conditions. In this Phase 1 study, the product will be primarily a statistical summary of the relevant meteorological data. A Phase 2 project may be conducted which would utilize the Industrial Source Complex Short Term model to further study the potential for air concentrations under adverse conditions (Wagner, 1987).
  • Objectives
  • Examine the weather patterns in Lompoc Valley to determine if there are periods of time when pesticide applications might result in higher ambient pesticide concentrations.
  • For outgassing, this analysis is based on the U.S. EPA procedure for determining meteorological stability class (U.S. EPA, 1986). Air concentrations are generally higher under stable, compared to unstable air conditions due to greater vertical mixing during the unstable conditions. In addition, recent draft guidelines for minimizing spray drift suggest that drift is minimized if application can be made when wind speed is between 2-10 mph (U.S. EPA, 1995). By obtaining meteorological data from Lompoc, and classifying the hours into the appropriate stability class, seasonal trends in stability can be determined.
  • Similarly, seasonal trends in wind speed can be determined with reference to the suggested guidelines of 2-10 mph.
  • Compare Lompoc meteorological data to data from other coastal meteorological stations in California's agricultural areas to determine if unusual conditions exist in Lompoc.
  • Procedures
  • Obtain and assemble data
  • Lompoc
  • Obtain several years of hourly local meteorological data from two Santa Barbara County Air Pollution Control District monitoring sites located in and near Lompoc.
  • 2 sites
  • H St. located in downtown Lompoc on H St. between Ocean and Cypress at an elevation of about 100' above sea level
  • HS & P station located about 1.8 km (1.1 mi) NNE of intersection of Harris Grade and Rucker Rd. at an elevation of about 650' above sea level. This station is about 6.3 mi NNE of intersection of H St. and Ocean St. in downtown Lompoc.
  • Data to obtain
  • wind direction
  • wind speed
  • standard deviation of wind direction
  • Obtain net radiation data
  • Net radiation can be obtained from California Irrigation Management Information System (CIMIS) weather data system, operated by the Department of Water Resources. Station #38 located in Santa Maria is on approximately the same longitude as Lompoc. The net radiation data is used to distinguish between night and day.
  • Assemble data into database format
  • Assemble 3 separate records, each an hourly record data, into a single record in order to compare stations and to utilize CIMIS data to estimate stability.
  • Other meteorological stations in coastal areas
  • Process and organize data as needed following preceding outline
  • Other potentially relevant data
  • Vandenberg AFB mixing height data.
  • Analyze data
  • Estimate hourly stability class using standard deviation of horizontal wind direction as outlined in Guideline on Air Quality Models (1986).
  • Provide statistical summaries by month of wind factors relating to outgassing
  • Frequency of stability class
  • Wind direction
  • Wind speed
  • Provide statistical summaries by month of wind factors relating to drift
  • Frequency of wind speed in three categories: less than 2 mph, between 2 mph and 10 mph and greater than 10 mph based on draft guidelines for aerial spraying (U.S. EPA, 1995)
  • Based on the statistical summaries, determine if there are monthly meteorological patterns which could lead to higher air concentrations of pesticides.
  • Perform more detailed analysis when appropriate to identify diurnal patterns of meteorological conditions. Take into account application patterns (Akers et al., 1995ab).
  • Compare Lompoc data with data from other sites.
  • Summarize and assess relevance of Vandenberg AFB data.
  • Provide written report of results including monthly wind directions, monthly frequency of stability classes, monthly frequency of wind speed conditions.
  • References

    Akers, Patrick, Janet Broome, Robert Hobza, Larry Wilhoit, Robert Teso, and Davis Supkoff. 1995a. An inventory of pest management practices in the Lompoc Valley. February 1995. PM 95-01. Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch, Pest Management Analysis and Planning Program.

    Akers, Patrick, Larry Wilhoit, Janet Broome, Robert Hobza, Robert Teso, and Davis Supkoff. 1995b. An inventory of pest management practices in the Lompoc Valley. Second Edition. August 1995. PM 95-02. Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch, Pest Management Analysis and Planning Program.

    The Thomas Guide. 1992 Santa Barbara and San Luis Obispo Counties. Map #876 and #916 reproduced with permission of Thomas Bros.

    U.S. EPA. 1986. Guideline on Air Quality Models (Revised). EPA-450/2-78-027R. Office of Air and Radiation, Office of Air Quality Planning and Standards, Research Triangle Park, NC. (Table 9-3 and 9-4 are the relevant tables).

    U.S. EPA. 1995. Aerial drift reduction advisory (attachment to letter from Peter Caulkins, Acting Directory Special Review and Reregistration Division of the U.S. EPA to Paul Liemandt [mispelled as Tiemandt])

    Wagner, Curtis P. 1987. Industrial source complex (ISC) dispersion model user's guide - second edition (revised -- Volume I. EPA-450/4-88-002a. Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency


    1. Maps showing location of two Lompoc weather stations
    2. Detailed meteorological data description for H St. and HS&P sites.
    3. Table 9-3 showing how stability classes are determined based on standard deviation of horizontal wind direction.
    4. Meta-code for algorithm to determine stability class.