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winter season. The median 24- hour measurement was 0.26 ach, with a range of 0.09 ach to 5.3 ach. A total of 67% of the homes had outdoor air exchange rates below the minimum California Building Code (2001) requirement of 0.35 ach. Thus, the relatively tight envelope construction, combined with the fact that many people never open their windows for ventilation, results in homes with low outdoor air exchange rates and higher indoor air contaminant concentrations. The MainPlace Mall project in Santa Ana, CA is surrounded by roads with moderate to high traffic (e.g. I-5, Garden Grove Freeway, Main Street). As a result of the outdoor traffic noise, this has been determined to be a sound impacted site according to the Addendum to the Final Environmental Impact Report (City of Santa Ana, 2019), with noise levels ranging from 54.4 to 68.6 dBA CNEL as reported in Table N-6, Existing Plus Project Traffic Noise Levels. As a result of the high outdoor noise levels, the current project will require the need for mechanical supply of outdoor air ventilation air to allow for a habitable interior environment with closed windows and doors. Such a ventilation system would allow windows and doors to be kept closed at the occupant's discretion to control exterior noise within residential interiors. PMz 5 Outdoor Concentrations Impact. An additional impact of the nearby motor vehicle traffic associated with this project, are the outdoor concentrations of PM2.5. According to the Addendum to the Final Environmental Impact Report (City of Santa Ana, 2019), this development is located in Santa Ana, which is a State and Federal non -attainment area for PMz.s. An air quality analyses should to be conducted to determine the concentrations of PMz.s in the outdoor and indoor air that people inhale each day. This air quality analyses needs to consider the cumulative impacts of the project related emissions, existing and projected future emissions from local PM2.5 sources (e.g. stationary sources, motor vehicles, and airport traffic) upon the outdoor air concentrations at the project site. If the outdoor concentrations are determined to exceed the California and National annual average PM2.5 10