1 Key Monitoring Issues Status of PM 2.5 monitoring methodologies Criteria for acceptance of monitors and sites Special considerations for comparing ambient data to the PM 2.5 NAAQS

2 PM 2.5 Monitoring Methodologies – Applicability by Objective NAAQS comparison –Federal Reference Methods (FRM) or Federal Equivalent Methods (FEM) must be used –Currently these methods only include filter-based samplers for PM 2.5 Air Quality Index and other public reporting objectives –Continuous monitors are favored due to availability of real time information and cost-effective support of daily sampling needs –Examples include Beta Attenuation monitors and TEOM monitors. These methods have known biases compared with FRM samplers which can vary by season and geographic area. Emergency Response –Portable monitors such as EBAMS are employed due to ease of set-up and flexibility to operate where utilities are compromised Decreasing Measurement Certainty Most precise Least precise

3 Post Katrina Monitoring in New Orleans, LA How different monitors can give different answers

4 Table E-4 of Appendix E to Part 58. Summary of Probe and Monitoring Path Siting Criteria PollutantScale (maximum monitoring path length, meters) Height from ground to probe, inlet or 80% of monitoring path 1 Horizontal and vertical distance from supporting structures 2 to probe, inlet or 90% of monitoring path 1 (meters) Distance from trees to probe, inlet or 90% of monitoring path 1 (meters) Distance from roadways to probe, inlet or monitoring path 1 (meters) PM,Pb 3,4,5,6,8 Micro: Middle, Neighborhood, Urban and Regional 2-7 (micro); 2-7 (middle PM ); 2-15 (all other scales) > 2 (all scales, horizontal distance only) > 10 (all scales)2-10 (micro); see Figure E-1 of this appendix for all other scales. National Regulations for Monitor and Site Acceptance Criteria Table E-4 of this appendix presents a summary of the general requirements for probe and monitoring path siting criteria with respect to distances and heights. It is apparent from Table E-4 that different elevation distances above the ground are shown for the various pollutants. The discussion in this appendix for each of the pollutants describes reasons for elevating the monitor, probe, or monitoring path. The differences in the specified range of heights are based on the vertical concentration gradients. For CO, the gradients in the vertical direction are very large for the microscale, so a small range of heights are used. The upper limit of 15 meters is specified for consistency between pollutants and to allow the use of a single manifold or monitoring path for monitoring more than one pollutant.

5 40 CFR part 58 Subpart D--Comparability of Ambient Data to NAAQS §58.30 Special considerations for data comparisons to the NAAQS (a) Comparability of PM2.5 data. (1) There are two forms of the PM2.5 NAAQS described in part 50 of this chapter. The PM2.5 monitoring site characteristics (see appendix D, section 4.7.1) impact how the resulting PM2.5 data can be compared to the annual PM2.5 NAAQS form. PM2.5 data that are representative, not of areawide but rather, of relatively unique population-oriented microscale, or localized hot spot, or unique population-oriented middle-scale impact sites are only eligible for comparison to the 24-hour PM2.5 NAAQS. For example, if the PM2.5 monitoring site is adjacent to a unique dominating local PM2.5 source or can be shown to have average 24-hour concentrations representative of a smaller than neighborhood spatial scale, then data from a monitor at the site would only be eligible for comparison to the 24-hour PM2.5 NAAQS.