Bret A. SchichtelCenter for Air Pollution Impact and Trend Analysis (CAPITA)

Washington UniversitySt. Louis, MO, 63130

Presented at EPA’s National Exposure Research Lab (NERL)

December 2, 1998

Local and Regional Contributions of PM2.5 to Urban Areas in the Mid-Atlantic and

Southwestern US

ObjectivesObjectives

Establish first order estimates and seasonality of the local and regional contributions of fine particulate mass to Mid-Atlantic and Southwestern US urban areas

MethodsMethods

• Urban Excess - compare urban PM2.5 seasonal trends to nearby rural sites

• Establish relationship between PM2.5 and wind speed and direction

• Surface winds• Regional transport winds derived from forward airmass histories

The National PM Research Monitoring NetworkThe National PM Research Monitoring Network• Primary objective - provide ambient air quality data for relating health effects to chemical and/or physical properties of PM and to support emerging regulatory implementation and development issues

• Fine and coarse speciated PM and meteorological data

Baltimore Maryland2/97 - 12/97

Phoenix Arizona 2

/95 - 12/97

Located about 2 miles from down town near a large park

located about 5 miles northwest of downtown Phoenix and 5 miles southeast of Glendale

Locations of PM2.5 and Surface Wind Monitoring SitesLocations of PM2.5 and Surface Wind Monitoring Sites The National PM Research Monitoring Network data was integrated with PM2.5 from IMPROVE, NESCAUM, and AIRS Data (1988 - 1997)

Mid-Atlantic Sites Southwest Sites

Mid-Atlantic PM2.5 Seasonal TrendsMid-Atlantic PM2.5 Seasonal TrendsWashington DC and Philadelphia have similar trends increasing 60% (15-25 g/m3) from spring to summer. Baltimore has lower cold season concentrations (9-12 g/m3)

The rural seasonal trend is similar to the urban sites with concentrations almost doubling from ~10 g/m3 during winter to 20 g/m3 during summer.

Urban Seasonal Trends - Baltimore, Washington DC and Philidelphia

Rural Seasonal Trends - Jefferson NF, VA, Brigantine, NJ and Ringwood, NJ

Urban Trends Rural Trends

Mid-Atlantic PM2.5 Urban ExcessMid-Atlantic PM2.5 Urban ExcessAt Washington and Philadelphia the winter excess is 4-8 g/m3 (20-40%) and 1-8 g/m3 (5-40%) in the summer. The excess at Baltimore varies between 0 - 10 g/m3 with no apparent seasonal pattern.

Seasonal Trends - Washington DC Brigantine, NJ & Jefferson, VA

Seasonal Trends - Baltimore Brigantine, NJ & Jefferson, VA

Washington ExcessWashington Excess Baltimore ExcessBaltimore Excess

Urban Seasonal Trends - Phoenix, Long Beach, Calexico, and El Centro.

Rural Seasonal Trends - Hopi Point, Bryce Canyon, Tonto, Saguaro, and Petrified Forest

Southwest PM2.5 Seasonal TrendsSouthwest PM2.5 Seasonal TrendsUrban sites are winter peaked with 50% more PM2.5 during Dec. then spring.

Rural sites are Spring-Summer peaked with 50% more PM2.5 during June than Jan.

Urban TrendsUrban Trends Rural TrendsRural Trends

Phoenix Arizona Urban ExcessPhoenix Arizona Urban ExcessThe Largest excess occurs during the fall and winter at 9-18 g/m3 (50 – 90%). This decreases to 3 – 6 g/m3 (30 – 70%) during the Spring and Summer.

Seasonal Trends - Phoenix, Hopi Point, Tonto, and Petrified Forest

Phoenix ExcessPhoenix ExcessLocal and Regional Contributions

Winter SummerConc.g/m3

% PM2.5 Conc. g/m3

% PM2.5

Local 9 – 18 50 – 90% 3 – 6 30 – 70%

Regional 2 – 5 10 – 50% 4 – 7 70 – 30%

PM2.5 as a Function of Wind Speed and DirectionPM2.5 as a Function of Wind Speed and Direction

Schematic illustration of a simple one-dimensional model

Concentration as a function of wind speed at different local source strengths

Concentration Vs Wind Speed

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8 9 10Wind Speed, m/s

Co

nce

ntr

atio

ns,

g

/m3

QL/H = 0 QL/H = 10 QL/H = 20 QL/H = 30

Background, 10 g/m3

Wind Speed and DirectionWind Speed and Direction

Surface Winds:

• Low lying instantaneous winds - influenced by local terrain• Identify the local dispersion characteristics. • Different locations from PM monitoring sites

Regional Transport Winds:

• The regional transport winds are a regional dispersion index that takes into account three days of airmass history dispersion.

• Accounts for recirculation and changes in transport speed and direction with height

• Problems with the regional transport winds:

• Dependent on modeled meteorological data which are subject to errors and biases.

• Dependent on the maximum particle age used in the airmass history. No sensitivity testing has been conducted at this point.

Creation of Regional Transport Winds from Airmass HistoriesCreation of Regional Transport Winds from Airmass Histories

Three day forward airmass histories were calculated from 504 source evenly distributed over North America using the CAPITA Monte Carlo Model and NGM wind fields. Twelve airmass histories per day from 1991 - 1995

NGM GridSource Location

Creation of Regional Transport Winds from Airmass HistoriesCreation of Regional Transport Winds from Airmass Histories

Transport Speed: A measure of the airmass residence time between the source and receptor.

Transport Direction Rose: A frequency distribution of the directions that the particles at the receptor came from. The particle direction is the angle, , between north and the straight line from the receptor to the particle’s source.

Source1

Source2

Mid - Atlantic PM2.5 Vs Surface Wind Speed Mid - Atlantic PM2.5 Vs Surface Wind Speed Cold Season (October - March) Cold Season (October - March)

Urban sites have sharp declines (60%) with increasing wind speeds, while rural sites have smaller decline. Implications: Urban sites are dominated by local contributions and rural sites by regional. The high speed regional PM2.5 is 5-8 g/m3 for both urban and rural sites

5-8 g/m36-8 g/m3

Mid - Atlantic PM2.5 Vs Surface Wind SpeedMid - Atlantic PM2.5 Vs Surface Wind SpeedWarm Season (April - September)Warm Season (April - September)

Urban and rural sites show less PM2.5 decline (0-50%) with increasing wind speeds. Implication: summer PM2.5 concentrations have larger local contribution than rural sites, but less than during the cold season. The high speed regional PM2.5 is 8-18 g/m3 for urban and 11 g/m3 or rural sites

8-18 g/m3

11 g/m3

Mid - Atlantic PM2.5 Vs Regional Transport Speed Mid - Atlantic PM2.5 Vs Regional Transport Speed Warm Season (April - September) Warm Season (April - September)

Urban and rural sites have steep PM2.5 declines (80%) with increasing wind speeds. Implication: Regional transport winds are unable to distinguish between locally and regionally dominated source contributions. The high speed regional PM2.5 is 8-14 g/m3. The high speed regional PM2.5 during cold season is 5-12 g/m3 (note shown)

10-14 g/m3

8-10 g/m3

Surface Winds Regional Transport Winds

Washington PM2.5 Vs Wind Speed and Direction Washington PM2.5 Vs Wind Speed and Direction Warm Season (April - September) Warm Season (April - September)

Highest PM2.5 concentrations came from the southwest - northwest (180-270-360)’

Directional differences were more apparent with the regional transport winds

Southwest PM2.5 Vs Surface Wind Speed Southwest PM2.5 Vs Surface Wind Speed Cold Season (October - March) Cold Season (October - March)

Urban sites have sharp declines (over 60%) with increasing wind speeds, while rural sites are nearly independent of wind speed . Implication: Urban sites are dominated by local contributions and rural sites by regional. The high speed regional PM2.5 at Phoenix is 6 g/m3 and 2-4 g/m3 at the rural sites

7 g/m3

2-4 g/m3

Southwest PM2.5 Vs Surface Wind SpeedSouthwest PM2.5 Vs Surface Wind SpeedWarm Season (April - September)Warm Season (April - September)

Urban sites have small declines (25%) with increasing wind speeds while rural sites are nearly independent of wind speed. Implication: Warm season PM2.5 is less dependent on local sources than during the cold season. The high speed regional PM2.5 at Phoenix is 8 g/m3 and 5 g/m3 at the rural sites

8 g/m3

5 g/m3

Southwest PM2.5 Vs Regional Transport Speed Southwest PM2.5 Vs Regional Transport Speed Cold Season (October - March) Cold Season (October - March)

The high speed regional PM2.5 at Phoenix is 11 g/m3 and 2-4 g/m3 at the rural sites

PM

2.5

g/m

3

2-4 g/m3

11 g/m3

2-4 g/m3

ConclusionsConclusionsUrban & Rural Seasonal Trends - Urban Excess

Winter SummerConc. g/m3 % PM2.5 Conc. g/m3 % PM2.5

Local 4 – 8 20 - 40% 1 – 8 5- 40%Washington& Phili. Regional 10 – 12 60 - 80% 14 – 20 60-95%Phoenix Local 9 – 18 50 – 90% 3 – 6 30 – 70%

Regional 2 – 5 10 – 50% 4 – 7 30 – 70% The Baltimore local contributions are generally lower than Washington’s and Philadelphia’s

varying between 0 and 60%.

PM2.5 as a Function of Transport Speed and Direction Urban sites have larger regional contributions during the warm season (April – Sept.)

- Urban sites have larger PM2.5 declines with increasing wind speeds during the cold season Highest Mid Atlantic PM2.5 level occur during Southwest to Northwest regional transport winds.

High Speed Regional Contributions (g/m3):

Mid-Atlantic StatesCold Season Warm Season

Urban Rural Urban RuralMid-Atlantic Surface Winds 7 5 – 7 8 – 10 (18) 11

AMH Winds 7-12 6-10 9-15 8-10Southwest Surface Winds 7 3 5 5

AMH Winds 10 2 – 4