# Presentation: 686393

## Meteorology and Air Quality

- Processes that influence air quality
- Sunlight
- Horizontal dispersion
- Vertical mixing
- Transport
- Clouds and precipitation
- Large scale to local scale

## Basic Weather

- Aloft ridges and troughs
- Rising and sinking air
- Surface highs and lows
- Ridges, troughs, and temperature soundings
- Inversions
- Stability
- Mixing
- Clouds and precipitation
- Winds
- Synoptic scale
- Meso- and local-scale
- Transport (surface and aloft)

**Notes:**
Relate to processes on prior slide

## Aloft Ridges and Troughs (1 of 3)

- Mountains and valleys of warm and cool air
- The height of the 500-mb pressure altitude depends on the relative temperature of the column

**Notes:**
1.  Columns of cool and warm air

## Aloft Ridges and Troughs (2 of 3)

- Waves (ridges and troughs) generally move west to east
- Winds generally travel faster around ridges and slower around troughs
- Areas of aloft convergence and divergence

**Trough**

**Surface**

**500 mb**

**Wave movement**

**Fast wind**

**Ridge**

**Slow**

**Fast**

## Aloft Ridges and Troughs (3 of 3)

- Aloft divergence causes rising motion and a surface low
- Aloft convergence causes sinking motion and a surface high
- Surface pressure patterns are offset from aloft patterns

**Surface**

**500 mb**

**Trough**

**Ridge**

## Rising and Sinking Air 

- Sinking motion
- Warms the air
- Creates stable conditions
- Reduces vertical mixing
- Creates clear skies
- Associated with poor air quality
- Rising motion
- Cools the air
- Creates unstable conditions
- Increases mixing
- Causes cloud cover
- Associated with good air quality

**Notes:**
Besides sinking causing the surface highs ......

## Surface Highs and Lows – Relationship to Aloft Pattern (1 of 2)

- 500-mb heights on the afternoon of January 7, 2002 (00Z Jan 8)

- Surface pressure on the afternoon of January 7, 2002 (00Z Jan 8)

- High PM2.5 in Salt Lake City, Utah

**Notes:**
January 7, 2002   24-hr avg = 32 ug/m3
show area of convergence and sinking
Dome of warm air,  inter-mountain west

## Surface Highs and Lows – Relationship to Aloft Pattern (2 of 2)

- Low PM2.5 in Salt Lake City, Utah

- 500-mb heights on the afternoon of January 22, 2002 (00Z Jan 23)

- Surface pressure on the afternoon of January 22, 2002 (00Z Jan 23)

- Surface Highs and Lows – Relationship to Aloft Pattern (2 of 2)

**Notes:**
January 22, 2002   24-hr avg = 9 ug/m3
Low over s. colorado  moved through area

## Life-cycle of Aloft and Surface Patterns

- Surface High
- Approaching Ridge

- Backside Surface High
- Warm Front
- Approaching Trough

- Surface Low
- Cold Front
- Trough

## Ridges and Temperature Soundings

- Ridge =
- Sinking =
- Strong Inversion =
- Poor Air Quality

- T

- Td

- Salt Lake City, Utah, temperature and dew point temperature sounding on January 7, 2002, at 0500 MST

**Notes:**
Ack tons of lines
point out  couple features
Strong inversion all day
1200 m MSL  Inversion at 850 mb 1500 m

## Troughs and Temperature Soundings

- Trough =
- Rising =
- No Inversion =
- Good Air Quality

- T

- Td

- Salt Lake City, Utah, temperature and dew point temperature sounding on January 22, 2002, at 0500 MST

**Notes:**
No inversion in morning, very little of one in evening

## Inversions

- Subsidence
- Created by sinking air associated with ridges
- Can limit daytime mixing depth and plays important role in daytime pollutant concentrations
- Nocturnal
- Created by cooling ground at night
- Strongest with clear skies, light winds, and long nights
- Can trap emissions, released during the overnight hours, close to the ground
- Advection
- Created when warm air aloft moves over cooler air below
- Can occur ahead of an approaching cold front
- Can cause poor air quality, despite the lack of an aloft ridge

## Inversions and Mixing

- Pollutants mix into a large volume resulting in low pollution levels

- Weak and high inversion

- Sunrise

- Sunset

**Height**

- Midnight

- CBL

- Temperature soundings

- Inversion Breaks

- NBL

- NBL

- RL

**Notes:**
Putting it all inversion and mixing GO SLOW ANIMATE

## Mixing and Temperature Soundings – Estimating Mixing Height

- _Holzworth Method_ – Starting at the forecasted maximum temperature, follow the dry adiabat (dashed line) until it crosses the morning sounding.  This is the estimated peak mixing height for the day.
- The dry adiabatic rate is the rate at which an unsaturated air parcel cools as it rises.  It is defined as -9.8oC per km.
- Uncertainty in mixing height estimates can be caused by changes in aloft temperatures or errors in predicted maximum temperatures.

- Estimated mixing height

- Forecasted max. temp.

- Dry adiabat

**2000 m**

**1000 m**

**1500 m**

** ****500 m**

- T

**Notes:**
Explain dry adiabat and parcel temp change as rises

## Stability – Beyond Inversions

- A measure of the ability of an air parcel to rise
- Inversions create stable conditions
- Stable conditions in a temperature profile can exist without an inversion

## Clouds and Precipitation (1 of 2)

- Clouds form when the air becomes saturated
- Adding water vapor
- Cooling air
- Many processes add water vapor or cool air
- Rising motion
- Trough
- Daytime heating
- Cold front undercutting warm air (or vice versa)
- Orographic
- Air in contact with cooler surface
- Air moving over water
- Others

## Clouds and Precipitation (2 of 2)

- Clouds and fog can increase the conversion of sulfur dioxide to sulfate from 1% per hour to 50% per hour
- Important in the East where one-half of PM2.5 is sulfate
- Clouds reduce ozone photochemistry
- Precipitation removes PM10 but has little direct impact on PM2.5
- Convective clouds can vent pollution from the  boundary layer under stable conditions
- Inhibits heating and ability to break inversion (mid and high clouds)

## Winds

- Horizontal dispersion and transport
- Synoptic scale
- Winds are driven by large high- and low-pressure systems
- Meso- and local-scale
- Land/sea or lake breeze
- Mountain/valley
- Terrain forced
- Diurnal cycles
- Foster stagnation and recirculation
- Local flows are often difficult for weather models to predict but can be predicted by forecasters with knowledge of the area
- Surface vs. boundary layer
- Transport at different levels
- Mixing during the day

**Notes:**
Meso-scale important to local aq

## Winds – PM2.5 Variation with Synoptic Pattern

**Low **
**PM****2.5**

**High **
**PM****2.5**

**High **
**PM****2.5**

**Moderate**
**PM****2.5**

**Lines of constant surface pressure**

**Line of constant 500-mb height**
**General synoptic surface flow**

- Adapted from Comrie and Yarnal (1992)

**Notes:**
Focus on Mid-Atlantic region

## Winds – Mesoscale (1 of 2)

**Surface winds on July 18, 1991, at (a) 0600 CDT and (b) 1500 CDT.  Peak ozone concentrations on this day were about 170 ppb.  (Dye et al., 1995)**

## Winds – Mesoscale (2 of 2)

- With a strong inversion and the surrounding mountains, surface winds are decoupled from the aloft winds.  The strong inversion and light surface winds allow for high PM2.5 concentrations.

**Notes:**
Clean out day  
Not a high ozone case
Another way to look at flows

## Transport

- 2-km satellite image from 1235 EST on 7/7/02

- Source: NASA

**The 24-hr average PM****2.5**** concentration ****in Boston on 7/7/02 was 62.7 μg/m****3**

- Backward trajectory ending at 0600 EST on 7/7/02

- Source: NOAA HYSPLIT

**Notes:**
Explain trajectory and background
Explain dates and 24 hour transport
Dirty air coming in not clean

## Summary – Meteorology Associated with Poor AQ

- Creates Temperature Inversion

- Reduces Vertical Mixing

- Ridge of High Pressure

- Poor Air Quality

- Summary – Meteorology Associated with Poor AQ

**Notes:**
Animate

## Summary – Meteorology Associated with Good AQ

- Rising Motion

- Cools, Moistens, and Destabilizes

- No Temperature Inversion

- Enhances Vertical Mixing

- Trough of Low Pressure

- Summary – Meteorology Associated with Good AQ

## Summary – Importance of Variables

## Summary

- Next step – Meteorological Products and Examples
- Questions

- Processes that influence air quality
-   Sunlight
-   Horizontal dispersion
-   Vertical mixing
-   Transport
-   Clouds and Precipitation