WeekendWeekday Ozone Observations in the South Coast Air Basin Sponsored by National Renewable Energ

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Weekend/Weekday Ozone Observationsin the South
Coast Air BasinSponsored byNational Renewable
Energy Laboratory and Coordinating Research
Council

• Eric Fujita, Robert Keislar, and William
  Stockwell
• Desert Research Institute
• University and Community College System of Nevada
• Reno, Nevada
• Paul Roberts, Hilary Main, and Lyle Chinkin
• Sonoma Technology, Inc.
• Petaluma, CA
• Weekend/Weekday Ozone Effect Workshop
• Sacramento, CA
• November 16, 1999

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Overview

• Conceptual explanation of the weekend/weekday
  ozone effect.
• Preliminary hypotheses
• NREL weekend/weekday study
• Other related studies

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What do we know about the weekend/weekday ozone
effect in the South Coast Air Basin?

• During 1986-93, ozone episodes occurred
  significantly more often on Saturdays than on
  Sundays through Wednesdays (Blier and Winer,
  1996).
• During 1992-94, large increases in ozone from
  Friday to Saturday (30) in many sites in
  central SoCAB, no change or slight decrease from
  Saturday to Sunday (Austin and Tran, 1999).
• Many sites show a Sunday effect in the 1996-98
  period (Austin and Tran, 1999).
• Weekend effect is least pronounced at transport
  sites further downwind (e.g., Lake Gregory,
  Banning, Hemet, Perris, and Santa Clarita).
  Coastal sites (Hawthorne and West Los Angeles)
  also exhibit a mild weekend effect (Austin and
  Tran, 1999).
• Decreases in peak ozone levels from the mid-1980
  to mid-1990 were greatest in western and central
  portions of the SoCAB. Greater reductions on
  weekdays than on weekends and hence the
  differences in WD vs. WE ozone maxima are larger
  now than the 1980s (Blier and Winer, 1996).
• Similar WE/WD effect in San Francisco Bay Area
  and cities in northeastern U.S., no effect in
  Sacramento, reserve effect in Atlanta.

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What do we know about the weekend/weekday
differences in VOC, NOx and PM in the South Coast
Air Basin?

• VOC, NOx and PM are all higher during weekdays.
• During 1986-93, average early morning NO2 and NOx
  were lower by 20-25 and 30-50, respectively on
  weekend days in the Coastal/Metropolitan region
  of the SoCAB. (Blier and Winer, 1996)
• Morning NOx is highest on weekdays, followed by
  Saturday and lowest on Sunday.
• Saturday afternoon levels are comparable to or
  slightly lower than weekday levels.
• Saturday evening levels tend to be lower than on
  Friday and roughly equal to or higher than the
  mean weekday evening levels.
• NOx mixing ratios are lower on Sunday than other
  days for all hours except at midnight to 4 a.m.
  when they are comparable to weekdays.
• The reactivity of the ambient hydrocarbon mixture
  has dropped between 1995 and 1996. Reactivity
  appears slightly lower on weekends (Franzwa and
  Pasek, 1999).
• 6 to 9 a.m.VOC/NOx ratios have decreased from 8
  to 10 in 1987 (SCAQS) to 4 to 7 in 1997.

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Historic Ozone Air Quality Trends South Coast
Air Basin (1976-1999))
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Historic Ozone Air Quality Trends South Coast
Air Basin (1980-1997) - WESTERN
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Historic Ozone Air Quality Trends South Coast
Air Basin (1980-1997) - CENTRAL
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Historic Ozone Air Quality Trends South Coast
Air Basin (1980-1997) - EASTERN
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Historic Ozone Air Quality Trends South Coast
Air Basin (1980-1997)
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Factors Affecting the Magnitude and Spatial
Extent of the WE/WD Ozone Effect

• Ozone formation depends on VOC, NOx and VOC/NOx
  ratios (O3 Potential).
• For VOC/NOx removing radicals and NOx to retard O3 formation.
  Under these conditions, a decrease in NOx favors
  O3 formation.
• At low NOx mixing ratios, or sufficiently high
  VOC/NOx, decrease in NOx favors peroxy-peroxy
  reactions, which retard O3 formation by removing
  free radicals from the system.
• At a given level of VOC, there exists an optimum
  VOC/NOx ratio at which a maximum amount of ozone
  is produced. For ratios less than this optimum
  ratio, increasing NOx decreases ozone. This
  situation occurs more commonly in urban centers
  and is the case for most of the central SoCAB.
• WE/WD differences in VOC and NOx emissions
  patterns (Diurnal and Spatial Distribution).
• Transport and ventilation (Meteorological
  Effects).
• Sea breeze limits ozone accumulation in the
  western portion of SoCAB.
• Increasing mixing height due to surface heating
  reduces VOC and NOx.
• Horizontal transport increases VOC/NOx ratios due
  to more rapid removal of NOx than VOC.

The observed "weekend effect" in the South Coast
Air Basin arises from differences in ozone
forming potential due to day-of-the-week changes
in ROG and NOx emissions. Variations in
meteorology affect the magnitude and spatial
extent of the WE/WD ozone effect within the
basin.
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Preliminary Hypotheses

• 1. Ozone formation in SoCAB, particularly the
  western and central portions of the basin, is
  VOC-sensitive with respect to ozone formation.
  VOC/NOx ratios are higher on weekends due to
  WE/WD changes in emissions resulting in greater
  ozone forming potential despite lower VOC and
  NOx on weekends.
• The weekend effect is greater where ?
  O3max/?VOC is greater during weekdays than
  during weekend days.
• WE/WD effect is most pronounced in area of the
  basin with the greatest NOx disbenefit (i.e.,
  most VOC-limited on weekdays).
• 2. The magnitude of the weekend effect is a
  function of the ozone forming potential and the
  time available for ozone formation before
  dilution offsets ozone formation.
• 3. The "weekend effect" is less pronounced in the
  eastern portion of the SoCAB where WE/WD
  differences in VOC and NOx emissions are masked
  by emission transport. Transport causes higher
  VOC/NOx ratios due to more rapid removal of NOx
  versus VOC as the emissions are transported
  toward the eastern side of the Basin.
• 4. Overnight carry-over of ozone, VOC and NOx
  from Friday and Saturday nights are greater than
  during other days of the week. Increased
  carryover is greater for VOC than for NOx. This
  affects the ozone forming potential of the
  ambient air.
• 5. A number of changes in emissions by
  day-of-week, time-of-day, and by location in the
  SoCAB can be postulated.

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Scope of Work

• PHASE I Retrospective Analysis of Ambient and
  Emissions Data and Refinement of Hypotheses
• Task 1 Review available emissions data. (STI)
• Task 2 Analyze retrospective ozone and ozone
  precursors and ozone episodes (DRI)
• Task 3 Review source apportionment analyses
  (DRI)
• Task 4 Analyze SCOS97-NARSTO meteorological and
  3-D ozone data (STI)
• Task 5 Synthesize phase I data analysis and
  prepare Phase 1 Report (DRI and STI)
• PHASE II Summer 2000 Field Measurements Program
• Task 6 Conduct field measurements (DRI)
• Task 7 Update and improve source composition
  profiles (DRI)
• Task 8 Update and improve temporally and
  spatially-resolved activity factors (STI)
• Task 9 Compile and validate data (STI)
• PHASE III Data Analysis and Final Report
• Task 10 Analyze temporal and spatial
  variations in O3, VOC, NOx and related air
  quality and meteorological parameters (DRI)
• Task 11 Analyze PAMS upper-air meteorological
  data (STI)
• Task 12 Update source apportionment analysis
  (DRI)
• Task 13 Analyze activity data (STI)
• Task 14 Update EKMA analysis (DRI)
• Task 15 Evaluate SCOS97-NARTSO model sensitivity
  results (STI)
• Task 16 Synthesize results and prepare final
  report (DRI and STI

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PHASE I Retrospective Analysis of Ambient and
Emissions Data and Refinement of Hypotheses

• Task 1 Review available emissions data. (STI)
• Based on available emission inventory data,
  identify VOC and NOx sources with potential to be
  different on weekends than on weekdays.
• Summarize diurnal variations in daily ROG and NOx
  emissions by day-of-the-week for these sources.
• Review the method(s) used to determine temporal
  variations and evaluate uncertainties and
  identify alternative methods or additional data
  that are available to update and improve existing
  temporal allocation of ROG and NOx emissions.
• Task 2 Analyze retrospective ozone and ozone
  precursors and ozone episodes. (DRI)
• Characterize and classify evolution of temporal
  and spatial patterns of O3, CO, total NMHC,
  carbonyl compounds, NOx, and NMHC/NOx ratios from
  Thursday to Monday during the summers of
  1995-1998 by meteorological conditions.
• Task 3 Review source apportionment analyses.
  (DRI)
• Review the source apportionment analysis
  conducted by the Desert Research Institute for
  SoCAB PAMS data (1994-97) for weekend days and
  weekdays.
• Review available source composition profiles and
  identify source for which updated profiles are
  needed.

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PHASE I Retrospective Analysis of Ambient and
Emissions Data and Refinement of Hypotheses

• Task 4 Analyze SCOS97-NARSTO meteorological and
  3-D ozone data. (STI)
• Evaluate meteorological conditions during
  SCOS97-NARSTO IOPs to determine applicability of
  weekend IOPs for assessments of the weekend
  effect.
• Characterize the surface and aloft spatial and
  temporal patterns of ozone and ozone precursors
  during weekend intensive operational periods.
• Analyze the data from the SCOS97 upper-air
  meteorological network and evaluate the regional
  representativeness of the temporal and spatial
  variations in wind and mixing heights that can be
  obtained from the two PAMS profilers (at LAX and
  Ontario) alone.
• Task 5 Synthesize phase I data analysis and
  prepare Phase 1 Report (DRI and STI)
• Summarize results of phase I data analysis,
  revise conceptual model, update hypotheses, and
  finalize field measurement program.
• Submit draft report for Phase I in April 2000.

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PHASE II Summer 2000 Field Measurements Program

• Task 6 Conduct field measurements (DRI)
• Continuous NOy and NOy (NOy-HNO3 at Pico Rivera,
  Azusa, and Upland.
• Continuous total NMHC by TEI 55 at Azusa and
  Upland.
• Continuous CO by TEI 48C-TL (0.4 ppb) at Pico
  Rivera, Azusa, and Upland. The District
  typically reports CO to the nearest ppm.
• Continuous light absorption by aethalometer at
  Pico Rivera, Azusa and Upland.
• DRI comparison with speciated NMHC from the
  SCAQMD auto-GC and TEI 55.
• Optional
• EC and OC by RP carbon analyzer or automated
  Thermal Optical Reflectance at Pico Rivera and
  Upland.
• Continuous PM mass by at Pico Rivera, Azusa and
  Upland.
• Supplemental canister and DNPH samples at Upland
  during weekends (Friday-Sunday) to fill in the
  PAMS every third day sampling. Collect a total
  of up to 72 canister and 72 DNPH cartridge
  samples.
• NO2 and PAN
• Continuous HCHO

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PHASE II Summer 2000 Field Measurements Program

• Task 7 Update and improve source composition
  profiles (DRI)
• Collect additional VOC source composition
  profiles identified in Task 1 and 4.
• Conduct saturation monitoring near epicenter of
  non-mobile VOC source to determine source
  composition and zone of influence.
• Task 8 Update and improve temporally and
  spatially-resolved activity factors (STI)
• Gather and compile existing information and new
  data that will support weekend-weekday
  comparisons of emissions as determined in the
  plan developed in Phase I.
• Task 9 Compile and validate data (STI)
• Compile and validate the SCAQMDs PAMS VOC data
  NOx, CO, and ozone data and upper-air data
  collected during the ozone seasons of 1999 and
  2000.

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PHASE III Data Analysis and Final Report

• Task 10 Analyze temporal and spatial
  variations in O3, VOC, NOx and related air
  quality and meteorological parameters (DRI)
• Task 11 Analyze PAMS upper-air meteorological
  data (STI)
• Task 12 Update source apportionment analysis
  (DRI)
• Task 13 Analyze activity data (STI)
• Task 14 Update EKMA analysis (DRI)
• Task 15 Evaluate SCOS97-NARTSO model sensitivity
  results (STI)
• Task 16 Synthesize results and prepare final
  report (DRI and STI

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