# Presentation: 457024

## UNDERSTANDING THE EFFECTIVENESS OF PRECURSOR REDUCTIONS IN LOWERING8-HOUR OZONE CONCENTRATIONS

- Steve Reynolds
- Charles Blanchard
- Envair
- 12 Palm Avenue
- San Rafael, CA  94901
- Telephone/fax:  (415) 457-6955
- E-mail:  steve@sreynolds.com

- May 22, 2002

## Purpose of the Study

- Develop a better understanding of the physical and chemical mechanisms underlying observed ozone trends
- Assess the technical feasibility of attaining the 8-hour ozone standard

- May 22, 2002

## Key Findings

- Various VOC and NOx emissions reductions  effective in reducing peak 1-hour ozone levels
- VOC reductions have modest impact on peak 8-hour ozone concentrations
- Anthropogenic NOx emissions must be reduced by 90 percent to reach the 8-hour ozone standard

- May 22, 2002

## Key Findings

- Anthropogenic VOC reductions ineffective because biogenic VOC, less reactive VOC, and CO continue to produce ozone
- Effectiveness of NOx reductions offset by an increase in ozone produced per NO
- Such NOx reductions may increase ozone levels in some areas
- These results call into question the technical feasibility of attaining the 8-hour ozone standard

- May 22, 2002

## Overview of Study Approach

- Combined application of
- analyses of ambient measured ozone data
- photochemical modeling with process analysis
- Employ modeling to provide insights into physical and chemical processes associated with ozone formation

- May 22, 2002

## Photochemical Modeling

- Choice of study area based on soundness of existing model application and availability of code with process analysis facilities
- SARMAP domain in central California
- SARMAP Air Quality Model (SAQM) with process analysis

- May 22, 2002

## Photochemical Modeling

- Extensive field measurements during summer of 1990 to support model application and evaluation
- 2-6 August 1990 ozone episode
- MM5 used to develop meteorological inputs
- Recent updates to emissions inventory by CARB

- May 22, 2002

## SAQM Emissions Sensitivity Results

- Array of VOC and NOx sensitivity runs performed by CARB using 1999 emissions
- Anthropogenic VOC and NOx emissions reduced from base case levels in 10 percent increments
- Results used to produce peak 1- and 8-hour EKMA-type isopleth diagrams

- May 22, 2002

## SAQM Emissions Sensitivity Results

- Isopleth diagrams developed using results for
- entire study domain
- San Jose  (24 km x 24 km)
- Stockton  (36 km x 72 km)
- Fresno  (60 km x 48 km)
- Visalia  (36 km x 48 km)
- Bakersfield  (36 km x 48 km)
- Tulare Lake  (36 km x 36 km)

- May 22, 2002

## SAQM Runs with Process Analysis

- 1990 and 1999 base case emissions
- VOC reductions ranged from 4 to 39 percent
- NOx reductions ranged from -7 to 41 percent
- CO reductions ranged from 3 to 43 percent
- Additional runs with anthropogenic VOC and NOx reduced to 50 and 25 percent of 1999 base case values

- May 22, 2002

## 1990 and 1999 Domain-wide Emissions

- May 22, 2002

## Percentage Change in 1999 VOC, NOx, and CO Emissions Relative to 1990 Values

- May 22, 2002

## Model Predicted Peak Ozone Levels

- Peak 1- and 8-hour ozone isopleth diagrams for 5 and 6 August based on 1999 emissions
- domain-wide
- San Jose, Stockton, Fresno, Visalia, Bakersfield and Tulare Lake
- Various combinations of VOC and NOx emissions reductions effective in reducing peak 1-hour ozone

- May 22, 2002

## Model Predicted Peak Ozone Levels

- VOC emissions reductions have modest impact on peak 8-hour ozone concentrations
- Anthropogenic NOx emissions must be reduced by 90 percent to reach level of 8-hour standard over entire domain

- May 22, 2002

## Model Predicted Peak Ozone Levels

- With significant NOx controls, VOC reductions have small additional benefit
- Biogenic VOC emissions with small amount of anthropogenic emissions sufficient to produce peak 8-hour ozone levels at or exceeding the 8-hour standard somewhere in the domain

- May 22, 2002

## Slide 16

- May 22, 2002

## Slide 17

- May 22, 2002

## Slide 18

- May 22, 2002

## Slide 19

- May 22, 2002

## Slide 20

- May 22, 2002

## Slide 21

- May 22, 2002

## Process Analysis Results

- Useful elements of process analysis results
- NO cycles (~ ozone produced per NO)
- mass of NO reacted
- mass of VOC reacted
- ozone created
- Ozone production involves
- radical initiation, propagation, and termination
- NO recreated by photolysis of NO2

- May 22, 2002

## Summary of key process analysis results for San Jose - August 5

- May 22, 2002

## Process Analysis Results for San Jose

- Lower precursor emissions in 1999 produce higher ozone relative to the levels formed in 1990
- Increased ozone forming efficiency in 1999
- 50 percent reduction in NOx emissions coupled with a 250 percent increase in NO cycles yields an increase in the mass of NO reacted...and ozone produced

- May 22, 2002

## Summary of key process analysis results for Stockton - August 5

- May 22, 2002

## Process Analysis Results for Stockton

- Ozone produced in 1999 comparable to 1990
- NO cycles increase, NO mass reacted decreases
- 50 percent NOx emissions scenario
- 40 percent increase in NO cycles
- net decrease in NO reacted
- 25 percent NOx emissions scenario
- 100 percent increase in NO cycles
- net decrease in NO reacted by 50 percent

- May 22, 2002

## Summary of key process analysis results for Bakersfield - August 5

- May 22, 2002

## Process Analysis Results for Bakersfield

- Ozone in 1999 ~ 10-30 percent lower than 1990
- total OH reacted is less in 1999
- 50 percent NOx emissions scenario
- increases in NO cycles offset by decreases in NO reacted in proportions similar to Stockton
- 25 percent NOx emissions scenario
- 100 percent increase in NO cycles
- net decrease in NO reacted by 50 percent

- May 22, 2002

## Summary of Process Analysis Results

- Reductions in NOx lowered 8-hour ozone concentrations but effectiveness offset by increases in NO cycles
- Substantial NOx emissions reductions required to reach 8-hour standard in Stockton and Bakersfield
- VOC reductions have little effect on either OH or NO cycles or the mass of VOC reacted

- May 22, 2002

## Summary of Process Analysis Results

- Anthropogenic VOC reductions
-  effective in lowering peak 1-hour ozone levels in areas where anthropogenic emissions dominate biogenic sources
- effectiveness limited in lowering peak 8-hour ozone due to contributions of biogenic VOC and anthropogenic CO emissions
- CO contribution to ozone produced significant  when VOC and NOx emissions at 25 percent level

- May 22, 2002

## Analyses of Ambient Ozone and Precursor Data in Central California

- Characterize trends, explain observed patterns, assess how patterns relate to modeling results
- Trends determined from annual statistics using t-tests of log-transformed data
- 4th highest 8-hour maximum, annual 1-hour maximum, and annual 1- and 8-hour maxima averaged over 21 days per year

- May 22, 2002

## Analyses of Ambient Ozone and Precursor Data in Central California

- Average diurnal concentration profiles for 21 high-ozone days
- Data separated into
- weekdays and weekends
- 3- and 5-year time periods

- May 22, 2002

## Observed Ozone Trends

- 4th-highest maximum daily 8-hour ozone concentrations declined at most sites in central California
- statistically significant (p<0.01) only at some sites in Bay Area and Stockton
- Annual 1-hour maxima also declined
- statistically significant at more sites

- May 22, 2002

## Trends in annual 4th-highest maximum daily 8-hour ozone concentration, 1980 through 2000.  Statistical significance (p<0.01) is indicated.

- May 22, 2002

## Trends in annual maximum daily 1-hour ozone concentration, 1980 through 2000.  Statistical significance (p<0.01) is indicated.

- May 22, 2002

## Diurnal  patterns of ozone, NOx and CO at the San Jose 4th Street site

- May 22, 2002

## Diurnal patterns of ozone, NOx and CO at the Stockton site

- May 22, 2002

## Diurnal patterns of ozone, NOx and CO at the Bakersfield sites

- May 22, 2002

## Mean maximum hourly ozone on Top 21 days:

- Comparable numbers of sites with increases and decreases

- May 22, 2002

## Mean maximum hourly O3/NOx on Top 21 days:

- Many more sites with increases than decreases

- May 22, 2002

## Mean maximum hourly O3/CO on Top 21 days:

- Many more sites with increases than decreases

- May 22, 2002

## Mean maximum hourly CO/NOx on Top 21 days:

- Many more sites with decreases than increases

- May 22, 2002

## Comparison of Modeling and Ambient Data Analysis Results

- Limitations of modeling results
- uncertainties in biogenic emissions estimates
- unclear whether ozone response for modeling period is representative of other days when moderate to relatively high 8-hour ozone concentrations occur

- May 22, 2002

## Comparison of Modeling and Ambient Data Analysis Results

- Consistency of modeling and ambient data analysis results
- both indicate modest changes in ozone levels over the period from 1990 to 1999
- observed changes in ambient NOx and CO corroborate the ~30 percent reduction in NOx and VOC emissions
- both indicate consistent increases in model NO cycles and ambient O3/NOx ratios

- May 22, 2002

## Consistent increases in:

-   > model-predicted NO cycles from 1990 to 1999
-   > ambient ozone/NOx ratios, 1989-91 and 1998-00

- May 22, 2002

## Consistent increases in:

-   > model-predicted NO cycles from 1990 to 1999
-   > ambient ozone/NOx ratios, 1989-91 and 1998-00

- May 22, 2002

## Consistent increases in:

-   > model-predicted NO cycles from 1990 to 1999
-   > ambient ozone/NOx ratios, 1989-91 and 1998-00

- May 22, 2002

## Frequency of occurrence (percent of hours) of limiting ozone precursor in central California areas for hours with ozone concentrations of 80-120 ppbv (left panel) and hours exceeding 120 ppbv (right panel).  March through October, 1994-2000. 

- Frequency of occurrence (percent of hours) of limiting ozone precursor in central California areas for hours with ozone concentrations of 80-120 ppbv (left panel) and hours exceeding 120 ppbv (right panel).  March through October, 1994-2000.

- May 22, 2002

## In all areas, frequency of NOx 

- Central California		1991-98
- Texas			1993-99
- Southern California		1994-97
- Atlanta			1994-99
- Northeast and mid-Atlantic		1994-99
- Southern Lake Michigan area		1994-98

- In all areas, frequency of NOx
- limited hours is greater for hours
- with ozone>120 ppbv (right)
- than for hours with ozone
- > 80 ppbv (left).

- May 22, 2002

## Extent of reaction during 1-hour and 8-hour episode days in 1994-2000 versus sequence of days within an episode

- May 22, 2002

## Conclusions

-  Various VOC and NOx emissions reductions  effective in reducing peak 1-hour ozone levels
- VOC reductions have modest impact on peak 8-hour ozone concentrations
- Anthropogenic NOx emissions must be reduced by 90 percent to reach the 8-hour ozone standard

- May 22, 2002

## Conclusions

- Anthropogenic VOC reductions ineffective because biogenic VOC, less reactive VOC, and CO continue to produce ozone
- Effectiveness of NOx reductions offset by an increase in ozone produced per NO
- Such NOx reductions may increase ozone levels in some areas
- These results call into question the technical feasibility of attaining the 8-hour ozone standard

- May 22, 2002

## Recommendations for Further Study

- Conduct data analyses and modeling in another area to assess consistency of findings with those obtained in central California
- northeastern U.S. using CMAQ

- May 22, 2002