Section 403 - PARTICULATE STANDARDS (PM[2.5])403.1 The concentration in the ambient air of particulate matter with an aerodynamic diameter of less than two point five (2.5) microns (PM2.5) shall not exceed: (A) Sixty five (65) micrograms per cubic meter of air as a 24 hour average based on the 3-year average of the 98th percentile of 24-hour PM2.5 concentrations.(B) Fifteen (15) micrograms per cubic meter of air as an annual arithmetic mean based on the 3-year average of the annual arithmetic mean PM2.5 concentrations.403.2 Sampling and analysis for particulates shall be conducted in accordance with Appendix A of this Regulation. Wash. Admin. Code Northwest Clean Air Agency, 400, 403