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The construction and operation of the Project would emit both PM10 and PM2.5. (See, e.g., Comment III and Draft EIR, Table 4.6-5.) The Draft EIR failed to estimate PM2.5 emissions. However, the PM10 emissions from combustion sources B-Ss are predominantly PM2.5. Further, a significant fraction of the fugitive dust cont. emissions is also PM2.5. (See, e.g., AP42.) Thus, the Project would contribute to an existing significant impact, the exceedance of ambient PM10 and PM2.5 standards. — These are new significant impacts that were not disclosed in the Draft EIR. VII. ODOR IMPACTS ARE SIGNIFICANT The Project includes an asphalt batch plant which is known to produce — malodors. (Draft EIR, p. 4.6-25.) The Draft EIR evaluated odor impacts by estimating the ambient concentration of hydrogen sulfide (H2S), one of the chemicals in asphalt plant emissions that is known to cause nuisance odors. This analysis yielded a maximum 1-hour H2S concentration of 28 µg/m3. (Ibid.) The Draft EIR concluded that the impact of odors from the Project is not significant because this maximum — concentration is less than the California ambient air quality standard for H2S of 42 µg/m3. (Ibid.) This is incorrect for three reasons. First, H2S is only one of many compounds in asphalt plant emissions that B-56 cause malodors.61 The Draft EIR ignored these other compounds. When multiple _ compounds cause odors, as here, the Dilution-to-Threshold ("D/T") method is commonly used to evaluate odor impacts. The odor units per cubic meter of air from a similar source is first determined through formal odor panel work as defined in ASTM E679-91. The facility then uses dispersion modeling to demonstrate that emissions will not cause a maximum off-site concentration to exceed a nuisance level, typically established at 5 D/Ts 62 The Draft EIR should be revised to include a — D/T analysis for the asphalt plant and recirculated for review. Second, the Draft EIR relied on the California H2S air quality standard as a nuisance threshold for purposes of determining significance of odors. This standard was established in the 1960s based on limited panel testing. The knowledge about H2S odor and methods to determine nuisance have advanced considerably since this standard was set. It is now well known that the nuisance odor threshold for H2S is much lower than the state standard and also much lower than the maximum _ concentration measured in the Draft EIXs study. 61 U.S.EPA,Hot Mix Asphalt Plant-Emission Assessment Report,Report EPA 454/R-00-109, December 2000. 62 See,for example,Richard J.Pope,Odor Regulatory Approaches. 44