Assessing PM2.5
Background Levelsand Local Add-On
Prepared by Bryan Lambeth, PEField Operations Support Division
Texas Commission on Environmental Quality
For presentation at the
National Air Quality Conference 2010
Houston Clear Houston Hazy
Causes of High PM2.5
• Regional and long-range transport– Haze, smoke, and/or dust already in the air coming
into an area from distant sources– Cannot be controlled by local mitigation measures
• Local primary and secondary sources– Local add-on of PM2.5 is increased by local air
stagnation, limited vertical mixing of the air, and high relative humidity
– Urban worst case is usually night-time winter stagnation with clear skies
Estimating Transport Contribution
• Upwind monitors and monitors that are not downwind of significant local sources provide the best estimate of incoming background levels from transport
• These monitors will usually have the lowest concentrations in the area
• Thus for areas with adequate peripheral monitoring coverage, the area lowest or second lowest concentration can serve to estimate the contribution from transport on most days
• The variation between the lowest and second lowest measurements may often indicate variability in the incoming background levels across an area with adequate monitoring coverage
Estimating Local Add-On
• Once the incoming background level has been estimated, concentrations higher than this background can indicate either variability in the background levels and/or add-on from local sources
• Subtracting the estimated background from a given measurement provides an estimate of impacts directly from local sources, but this estimate can be biased high when there is large spatial variability in the incoming background level
• Where speciation data are available for both background and add-on locations, the speciated components of local source impacts can also be evaluated by this method
Figure 1. Texas Coastal PM2.5 April-May 2008
0
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1/08
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
.
Galveston C34 TEOM National Seashore C314 TEOM Isla Blanca Park C323 FRMS
S
S
S SS
S - SmokeH - Continental haze
S
S
Figure 2. Texas Coastal PM2.5 June-August 2008
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0/08
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
.
Galveston C34 TEOM National Seashore C314 TEOM Isla Blanca Park C323 FRMS
D D
S - Mexican SmokeD - African DustH - Continental Haze
D
HS
H
H
DD
H
D
Houston-Galveston-Brazoria PM2.5 and Silicon 2008 Jun-Aug
0
5
10
15
20
25
30
35
40
45
50
1-Jun 1-Jul 1-Aug
Day (CST)
PM
2.5
(ug/
m3)
0
2
4
6
8
10
12
14
16
18
20
Silicon
(ug/m
3)
PM2.5 Max PM2.5 Min C8Ald C403Clnt C35DPk C303 Jef
S - Mexican Smoke D - African Dust H - Continental Haze
D
H
H
D
D
D
H
Houston-Galveston-Brazoria Daily PM2.5 February 2008
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Day CST
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
G1034T
H0024
H0024T
H0026T
H0058
H0416
H1034T
H1035
H1035T
H1039
H1039T
H1042T
H1050T
H0572T
M0078T
J0022T
Dallas-Fort Worth Daily PM2.5 February 2008
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Day CST
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
F1002
F1006
F1006T
F3011T
D0050
D0069
D0069T
D0087
N0034T
E0016
E0016T
E1044T
K0003T
Houston-Galveston-Brazoria Daily PM2.5 July 2008
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Day CST
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
G1034T
H0024
H0024T
H0026T
H0058
H0416
H1034T
H1035
H1035T
H1039
H1039T
H1042T
H1050T
H0572T
M0078T
J0022T
Dallas-Fort Worth Daily PM2.5 July 2008
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Day CST
Dai
ly A
vera
ge P
M2.
5 (u
g/m
3 lo
cal)
F1002
F1006
F1006T
F3011T
D0050
D0069
D0069T
D0087
N0034T
E0016
E0016T
E1044T
K0003T
14.012.5
Texas PM2.5 Annual Averages 2008
11.911.2
10.610.5
10.5
9.9
9.5
6.1
5.7
7.6
6.8
10.710.3
Micrograms/cubic meter
11.5
9.98.7
8.8
15.911.1
12.112.0
11.3
9.68.7
Texas PM2.5 Background Averages 2008
8.88.0
8.67.9
8.3
9.9
9.5
6.1
5.7
7.6
6.8
Micrograms/cubic meter
8.8
37.8%31.5%
Highest Annual Local Percent Add-On 2008
32.4%26.0%
25.3%18.7%
20.8%
Micrograms/cubic meter
16.9%
Conclusions
• For the areas analyzed, transport appears to account for at least about 70-80% of measured annual averages at sites with the greatest local source impacts
• At most about 20-30% of the annual average at analyzed sites with the worst local source impacts can be addressed by local control measures
Applications
• Analysis of “but for” considerations in determining exceptional event days– This approach could be used to estimate
whether a site would have exceeded the standard with a “normal” background level if the exceptional event had not occurred
• Estimating how much local add-on must be reduced to meet standards
• Model validation
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