NESCAUM Analysis Points to Need for More Stringent Annual and Daily PM2.5 Standards, 3-05
The Northeast States for Coordinated Air Use Management (NESCAUM) has prepared a detailed analysis of PM2.5 air quality data that demonstrates the need to tighten both the 24-hour and annual average PM2.5 standards.
The analysis shows that:
1. A change in either annual or 24-hr standard levels (and 24-hr percentile forms) shifts distribution curves and shaves maxima. Annual standards may fail to constrain 24-hr levels; 24-hr standards may fail to constrain annual levels. A suitable combination of appropriately stringent annual and 24-hr standards has optimum controlling effect throughout the distribution of PM2.5 levels. (Figures 1-2 and Tables 1-2)
2. Subdaily peak PM2.5 levels occur that the 24-hr averaging metric smoothes, masking exposure variability. Hourly averaged PM2.5 levels vary across days, weeks, and seasons. A 24-hr average standard can constrain subdaily maximum 1-, 3-, 4-, and 6-hr averages. The more stringent the 24-hr average standard, the lower the subdaily maximum levels will be. (Figures 3-6, Table 6)
A full copy of the analysis is attached.
Attachments
- NESCAUM PM2.5 Air Quality Analysis
- nescaum-comments32405.pdf
Nescaum comments on second draft staff paper.
