# Presentation: 781164

## OVERVIEW
Demonstrate the differences between O3 and PM2.5 episodes
Case 1: Stagnation with a twist
Case 2: Ice Station Greensboro
Case 3: Forecast “Jeopardy”
Case 4: When the smoke alarm goes off...
Putting it all together

- Case Studies of O3 and PM2.5 – Variation in North Carolina

- OVERVIEW
- Demonstrate the differences between O3 and PM2.5 episodes
- Case 1: Stagnation with a twist
- Case 2: Ice Station Greensboro
- Case 3: Forecast “Jeopardy”
- Case 4: When the smoke alarm goes off...
- Putting it all together

**Notes:**
For each subject discussed, an example will be provided with its URL.  At the end of the prepared slides are a series of pages containing lists of links for each category.

## Apply knowledge of meteorological processes and products to four “real-world” examples.

- Episodes were selected to demonstrate the different processes that affect O3 and PM2.5 over a range of concentrations and seasons.
- Upper-air and surface patterns
- Vertical mixing and stability
- Transport conditions and source regions
- Clouds and precipitation
- Unusual events

- Case Studies of O3 and PM2.5 – Variation in North Carolina

## Case 1: Stagnation With a TwistJuly 17 - 18, 2001 (1 of 3)

- Surface high and aloft ridge
- Warm temperatures at 850 mb
- Light winds with west-southwesterly trajectory
- Partly cloudy skies and low RH
- USG O3 and Moderate PM2.5

- Case 1: Stagnation With a TwistJuly 17 - 18, 2001 (1 of 3)

- Satellite IR and surface observations on
- July 17 at 1000 EST

- 850-mb winds and  temperature on July 17 at 1900 EST

- 24-hr backward trajectories ending on July 17 at 1900 EST

## Case 1: Stagnation With a TwistJuly 17 - 18, 2001 (2 of 3)

- High pressure ridge being “squeezed” from the north
- Increasing winds at 850 mb
- Clouds and precipitation move in
- Effect on air quality?

- Case 1: Stagnation With a TwistJuly 17 - 18, 2001 (2 of 3)

- Satellite IR and surface observations on
- July 18 at 1015 EST

- Meteogram for July 17 at 0700 EST through July 19 at 1900 EST.

## Case 1: Stagnation With a TwistJuly 17 - 18, 2001 (3 of 3)

- Daytime O3 AQI

- PM2.5 AQI

- Increasing cloud cover reduced ozone levels on 7/18.  Continued light surface winds allowed PM2.5 to rise as the stagnant air mass remained in place.

## Case 2: Ice Station Greensboro December 6 - 7, 2002 (1 of 3)

- Cold high pressure building over eastern U.S.
- Winds become lighter at the surface
- Clear skies
- Extensive ice and snow cover

- December 6, 2002

- Satellite IR and surface observations on
- December 6 at 1015 EST

## Case 2: Ice Station Greensboro December 6 - 7, 2002 (2 of 3)

- Intense overnight inversion forms in the highly stable atmosphere.  Emissions
- were trapped within the nocturnal boundary layer and reach higher concentrations.

- Case 2: Ice Station Greensboro December 6 - 7, 2002 (2 of 3)

- Inversion caps the nocturnal boundary layer

- Temp. sounding on 12/7 at 0700 EST for Greensboro, NC.

- Mixing depth and stability class for 12/5 at 1700 EST (00 UTC on 12/6) through 12/8 at 0400 EST (09 UTC on 12/8).

## Case 2: Ice Station Greensboro December 6 - 7, 2002 (3 of 3)

## Case 3: Forecast “Jeopardy” August 23 - 24, 2002 (1 of 4)

- August 24, 2002

- Code Orange level of PM2.5 from 8/23 decreased dramatically between
- 0800-1000 EST on 8/24.  What meteorological processes caused this change?

## Case 3: Forecast “Jeopardy” August 23 - 24, 2002 (2 of 4)

- Winston-Salem Observations (EDT)

- Case 3: Forecast “Jeopardy” August 23 - 24, 2002 (2 of 4)

## Case 3: Forecast “Jeopardy” August 23 -24, 2002 (3 of 4)

- A subtle trough does the trick

- Case 3: Forecast “Jeopardy” August 23 -24, 2002 (3 of 4)

- 850-mb winds and  temperature on August 23 at 1900 EST

- 850-mb winds and  temperature on August 24 at 0700 EST

- Surface analysis on August 24 at 0700 EST

## Case 3: Forecast “Jeopardy” August 23 -24, 2002 (4 of 4)

- Troughs can develop in the “lee” of mountains influencing the location of pollutant maxima.
- Falling surface pressure
- Low-level convergence
- Rising motion leading to clouds and precipitation
- Temporarily “stirs” the stagnant air masses

- Troughs and Air Quality

- Case 3: Forecast “Jeopardy” August 23 -24, 2002 (4 of 4)

- Surface winds and  pressure on August 24 at 1000 EST

## Case 4: When the Smoke Alarm Goes Off...November 2 - 5, 2000 (1 of 5)

- Visible satellite image on November 1 at 1622 EST

## Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (2 of 5)

- Fairly strong ridging over the east
- Clear, warm conditions
- Light N/NE winds
- Slowly approaching cold front
- Mid-moderate PM2.5 on 11/2/00
- Forecast for 11/3/00?

- Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (2 of 5)

- A benign weather pattern

- Satellite IR and surface observations on
- November 2 at 1100 EST

- Surface observations on
- November 2 at 1200 EST

- Meteogram for 11/2 at 0700 EST through 11/4 at 1900 EST.

## Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (3 of 5)

- from W.V. kept PM in mid-Moderate.

- Wind shift overnight on 11/2-11/3
- brought smoke “front” into Triad.

- Transport of smoke by winds caused...

- Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (3 of 5)

- 950-mb wind vectors and streamlines on 11/3 at 0700 EST

- 950-mb wind vectors and streamlines on 11/2 at 0700 EST

## Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (4 of 5)

- Key question:  How long will the episode last?  Need wind shift, increased speed, and increased mixing to dilute the air mass.

- PM2.5 levels reach Code Red

- Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (4 of 5)

## Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (5 of 5)

- Cold frontal passage and high building in from the NW strengthened the pressure gradient, increased mixing, and steered winds away
- from the forest fire source region.

- Case 4: When the Smoke Alarm Goes Off... November 2 - 5, 2000 (5 of 5)

- Cold front to the rescue

- NCEP 48-hour surface forecast valid on November 4 at 1900 EST

- Surface pressure and 950-mb winds on 11/5 at 0700 EST

## Putting it All Together

- Process is important to case studies

- Additional issues for forecast consideration
- Lake & sea breezes, mountain & valley effects
- “Calendar” effects (weekend, holiday, special events)
- Influence of nearby sources (point, mobile, area)
- Placement and treatment of continuous PM2.5 data
- Influence of control and awareness programs (wood burning, ozone coalitions)

-       * Lowest Importance
- **** Highest Importance

## Summary

- Identify which processes are most important to your forecast.
- Anticipate the difference between O3 and PM2.5 behavior.
- Don’t overlook subtle features – they can have big air quality impacts.

- Next step - Air Quality Forecasting Tools
- Questions