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Proposed PM 2.5 Calculation Methodology Significance Thresholds

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**1. **Proposed PM 2.5 Calculation Methodology & Significance Thresholds South Coast Air Quality Management District
Public Workshop
August 9, 2006

**2. **PM 2.5 – Background Primarily from combustion sources
Mobile sources - auto, trucks
Stationary sources – ICEs
Directly emitted or formed in atmosphere from combustion of gases (such as NOx and SOx combining with ammonia)
Focus is on directly emitted PM2.5 PM2.5 is particulate mater with an aerodynamic diameter less than or equal to 2.5 microns PM2.5 is particulate mater with an aerodynamic diameter less than or equal to 2.5 microns

**3. **PM2.5 Air Quality

**4. **Trends of Basin PM2.5 (µg/m3) Federal Annual Standard = 15 ug/m3
Federal 24-hour Standard = 65 ug/m3Federal Annual Standard = 15 ug/m3
Federal 24-hour Standard = 65 ug/m3

**5. **Ambient Air Quality Standards Federal PM 2.5 standards established in 1997
State PM 2.5 standards established in 2002
AQMD & CEQA significance thresholds for directly emitted PM2.5 yet to be developed
Proposed actions
PM2.5 calculation methodology
Regional & localized significance thresholds

**6. **PM2.5 Emission Calculation Methodology Calculate PM10 using standard methodologies and PM10 emission factors
Apply CARB’s PM2.5 fraction profiles by source category as default
CARB’s profiles used for AQMP inventories with public review process
Project-specific PM2.5 profiles acceptable Staff is recommending an indirect approach to calculating PM2.5 until such time as specific PM2.5 emission factors are developed
PM emissions typically contain specific fractions of PM10 & PM2.5
Since PM2.5 is a subset of PM10, if you know the amount of PM10 you can calculate the amount of PM2.5 based on its percent fraction of PM10 THEREFORE
Staff is recommending an indirect approach to calculating PM2.5 until such time as specific PM2.5 emission factors are developed
PM emissions typically contain specific fractions of PM10 & PM2.5
Since PM2.5 is a subset of PM10, if you know the amount of PM10 you can calculate the amount of PM2.5 based on its percent fraction of PM10

**7. **Significance Thresholds – Approaches No backsliding from PM10 thresholds
PM2.5 thresholds must be at least as stringent as PM10 thresholds
PM10 thresholds were used as a basis to develop PM2.5 thresholds
Reflects air quality & source emissions
Considers current nonattainment status of district & PM2.5 emission reductions necessary to demonstrate attainment
Considers emission source type, e.g., fugitive vs. combustion emissions Approaches for developing PM2.5 significance thresholds take into consideration the following issues:
PM2.5 significance thresholds were also developed taking into consideration the current PM2.5 nonattainment status of the district, i.e., substantial PM2.5 emission reductions are necessary to attain state and federal standards so thresholds were developed taking into consideration PM2.5 emission reduction needs of the district
Finally, the PM2.5 significance thresholds were developed taking into consideration the emission source type, for example fugitive dust PM has a much higher fraction of PM10 than PM2.5Approaches for developing PM2.5 significance thresholds take into consideration the following issues:
PM2.5 significance thresholds were also developed taking into consideration the current PM2.5 nonattainment status of the district, i.e., substantial PM2.5 emission reductions are necessary to attain state and federal standards so thresholds were developed taking into consideration PM2.5 emission reduction needs of the district
Finally, the PM2.5 significance thresholds were developed taking into consideration the emission source type, for example fugitive dust PM has a much higher fraction of PM10 than PM2.5

**8. **Proposed Localized Significance Thresholds (LSTs) LSTs – Construction = 10.4 µg/m3
Same as PM10 construction LST
~75% - 100% of emissions contributed from construction equipment engine exhaust depending on construction phase
More stringent than PM10 LST
Will prepare LST look-up tables for projects one through five acres in size
Localized significance thresholds recognize that projects may generate exposures or impacts to receptors in the vicinity of the project
LSTs were developed in response to the Board’s environmental justice initiatives and adopted by the Board in October 2003
So local public agencies do not have to perform dispersion modeling for projects less than or equal to five acres, staff back-calculated emissions that cause or contribute to an exceedance of the localized significance threshold and put these in tables based on size of the project, distance to the sensitive receptor & meteorology
Modeling performed using same construction scenarios used to develop LST look-up tables for other pollutants
If you don’t exceed the PM10 significance threshold you could still exceed the PM2.5 significance threshold because PM2.5 stays suspended in the atmosphere longer than PM10, which settles out at a predictable rate over distance
Localized significance thresholds recognize that projects may generate exposures or impacts to receptors in the vicinity of the project
LSTs were developed in response to the Board’s environmental justice initiatives and adopted by the Board in October 2003
So local public agencies do not have to perform dispersion modeling for projects less than or equal to five acres, staff back-calculated emissions that cause or contribute to an exceedance of the localized significance threshold and put these in tables based on size of the project, distance to the sensitive receptor & meteorology
Modeling performed using same construction scenarios used to develop LST look-up tables for other pollutants
If you don’t exceed the PM10 significance threshold you could still exceed the PM2.5 significance threshold because PM2.5 stays suspended in the atmosphere longer than PM10, which settles out at a predictable rate over distance

**9. **Proposed LSTs (Cont.) LST – Operation = 2.5 µg/m3
Same as PM10 operation LST
~99% of PM10 combustion emissions are PM2.5
Will prepare LST look-up tables for projects one through five acres in size For most projects, operational emissions are comprised primarily of mobile source combustion emissionsFor most projects, operational emissions are comprised primarily of mobile source combustion emissions

**10. **Proposed Regional Significance Thresholds (RST) PM2.5 RST – Operation & Construction = 55 #/day
PM2.5 emissions
Primarily from combustion
PM2.5 suspended for longer periods resulting in regional effects
EPA proposed significant emission rate of 10 tons per year for PM2.5 (Federal Register, Sept 8, 2005)
Recommend daily construction and operational PM2.5 RST consistent with EPA proposal
Regional significance thresholds are the thresholds that most of you are familiar with, adopted by the Board in 1993
RSTs ar the mass daily emissions from construction and operation
E.g., the RST for PM10 is 150 pounds per dayRegional significance thresholds are the thresholds that most of you are familiar with, adopted by the Board in 1993
RSTs ar the mass daily emissions from construction and operation
E.g., the RST for PM10 is 150 pounds per day

**11. **Next Steps Recommendations to Governing Board October 6, 2006
Effective Dates:
Begin public outreach after Board approval
Begin IGR commenting for NOPs/ISs 1/2007
Implement for new AQMD lead agency projects after Board approval
Highlight PM2.5 mitigation measures on AQMD CEQA webpages by 10/06