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
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
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)
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).
Examine the weather patterns in Lompoc Valley to determine if there are periods of
time when pesticide applications might result in higher ambient pesticide
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
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
Obtain and assemble data
Obtain several years of hourly local meteorological data from two Santa
Barbara County Air Pollution Control District monitoring sites located in
and near Lompoc.
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
Data to obtain
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.
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
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.,
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.
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
4. Meta-code for algorithm to determine stability class.