Techniques for Evaluating Wildfire Smoke Impacton Ozone for Possible Exceptional Events

Daniel Alrick1, Clinton MacDonald1, Brigette Tollstrup2, Charles Anderson2

1Sonoma Technology, Inc. (STI)2Sacramento Metropolitan Air Quality Management District (SMAQMD)

Presented at the National Air Quality ConferencesMarch 7–10, 2011

San Diego, CA

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What are Exceptional Events?

“Unusual or naturally occurring events that can

affect air quality but are not reasonably preventable...”

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What Makes an Event Exceptional?

• To justify data exclusion, evidence must show that

1.“There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the area.”

2.“The event is associated with a measured concentration in excess of normal historical fluctuations, including background.”

3.“There would have been no exceedance or violation but for the event.”

• The “but for” clause is often the most difficult to satisfy– No one data set necessarily has all the information– Availability and use of good meteorological data and

analysis tools is critical

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Northern California Wildfires, Summer 2008

Smoke on July 11, 2008

Basin Complex 2008

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Northern California Wildfires, Summer 2008

Fires started by lightning in June 2008

Below average precipitation across

California during February through June 2008

Drought, Lightning, and Fires

Lightning strikes: more than 6,000 from June 20 to 21, 2008

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Wildfire Impact on Air Quality• Wildfire smoke contains VOCs, NOx, and PM

• During wildfires, several ozone exceedances occurred in the Sacramento area

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Unhealthy for Sensitive Groups

Unhealthy

Very Unhealthy

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Tools for Evaluating Impact of Smoke

• Conceptual model– Examination of local meteorological conditions on

days with high ozone concentrations

• Identification of matching days

• Regression analysis – Equations describing the relationship between

pollutant concentrations and meteorological parameters

Ozone = (Temp) ∙ m1 + (Wind Speed) ∙ m2 + ... + constant

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Conceptual Model (1 of 4)

• Describes meteorological conditions typical of high ozone levels

• Using surface and upper air observations, STI developed rules of thumb for high ozone levels in Sacramento

Meteorological Parameter Rule of Thumb

925 mb temperature from Oakland sounding

≥25°C

500 mb geopotential height over Sacramento

≥5,850 m

Sacramento high temperature ≥93°F

Sacramento morning wind speed <4 knots

Sacramento morning wind direction >150° and <270°

Fairfield morning wind speed <15 knots

Morning San Francisco to Sacramento pressure gradient

<3.0 mb

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Conceptual Model (2 of 4)

Did weather conditions meet the rules of thumb for high ozone levels?

Meteorological Parameter

Rules of ThumbSmoke Day

Observations

925 mb temperature from Oakland sounding

≥25°C 21°C

500 mb geopotential height over Sacramento

≥5,850 m 5,840 m

Sacramento high temperature

≥93°F 86°F

Sacramento morning wind speed

<4 knots 2 knots

Sacramento morning wind direction

>150° and <270° 190°

Fairfield morning wind speed

<15 knots 17 knots

Morning San Francisco to Sacramento pressure gradient

<3.0 mb 3.3 mb

Maximum 1-hr ozone concentration

161 ppb

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Conceptual Model (3 of 4)

• Primary pattern for high ozone levels is an upper-level ridge over the West Coast

• Surface thermal trough over Sacramento

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Conceptual Model (4 of 4)

Did the weather pattern fit with the conceptual model?

• Zonal upper flow across northern California – does not fit with conceptual model

• Surface thermal trough located near Sacramento

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Identification of Matching Days (1 of 2)

Compare days with and without smoke that have similar meteorological conditions and look at the difference in ozone concentrations.

Smoke Day Matching Day

Example of a relatively good match of upper-level patterns between smoke day and matching day.

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Identification of Matching Days (2 of 2)

Result:

Ozone concentrations are higher on smoke day compared to matching day.

Meteorological Parameter

Rules of ThumbSmoke Day

ObservationsMatching Day Observations

925 mb temperature from Oakland sounding

≥25°C 21°C 19°C

500 mb Geopotential height over Sacramento

≥5,850 m 5,840 m 5,830 m

Sacramento high temperature

≥93°F 86°F 84°F

Sacramento morning wind speed

<4 knots 2 knots 6 knots

Sacramento morning wind direction

>150° and <270° 190° 211°

Fairfield morning wind speed

<15 knots 17 knots 19 knots

Morning San Francisco to Sacramento pressure gradient

<3.0 mb 3.3 mb 3.2 mb

Maximum 1-hr ozone concentration

161 ppb 79 ppb

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Regression Tools (1 of 2)

• Developed using historical ozone observations (daily 1-hr maximum ozone)

• Compare model predictions to observed ozone concentrations on smoke days

Observation – Max. Prediction = Estimated Smoke Contribution

1-hour Maximum Ozone Concentration (ppb)

Date 00Z ETA 12Z ETA 12Z ETA MOS ObservedEstimated Smoke

Contribution

Smoke Day 1 76 77 72 161 85

Smoke Day 2 76 71 60 130 54

Smoke Day 3 116 109 118 166 48

Smoke Day 4 95 85 76 151 56

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Consider Regression Model Error (2 of 2)

• In model development, calculated error range on regression predictions for the entire data set

• Estimated smoke contribution to ozone ranged from 48 to 85 ppb on the four example smoke days

Error on most days (95%) was ±35 ppb

-100 -75 -50 -25 0 25 50 75 10012Z ETA

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Example for one model:Error (Model – Obs)

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Conclusion

Existing and proven forecasting tools can be useful in determining smoke impact on air quality.