San Diego County Air Pollution Control District

In San Diego the district does not set the numbers. The San Diego County Air Pollution Control District has not adopted numeric CEQA thresholds for land use projects. Its Environmental Review Guidelines of November 14, 2024 are procedural: they say that when the district is lead agency it applies CEQA Guidelines sections 15064 through 15064.7, and the district's CEQA web page points lead agencies to the County and City of San Diego for guidelines and thresholds. The working numbers in San Diego therefore come from two lead agency documents, and a report must name which one governs the project.

County of San Diego, 2007 screening level thresholds

The County's Guidelines for Determining Significance, Air Quality, dated March 19, 2007, borrow the district's Air Quality Impact Analysis trigger levels from Rule 20.2, written for new or modified stationary sources, and apply them to whole projects for comparison. Table 5:

Pollutant	lb/hr	lb/day	tons/yr
PM10	None	100	15
PM2.5	None	55	10
NOx	25	250	40
SOx	25	250	40
CO	100	550	100
Lead	None	3.2	0.6
VOC	None	75	13.7

The same values apply to construction and operation. The daily values are meant for ordinary construction and operational emissions; the hourly and annual values suit temporary sources such as emergency generators. Rule 20.2 has no VOC or PM2.5 triggers, so the County took the VOC value from South Coast's Coachella Valley threshold and the PM2.5 value from EPA's 2005 proposed fine particle implementation rule of 10 tons per year, which works out to 55 lb/day. The 13.7 tons per year VOC figure is 75 lb/day times 365 divided by 2,000.

• Ozone precursors, PM10, PM2.5. Exceeding the screening level is a significant impact, because the basin is nonattainment for ozone and particulates. For PM10 the County adds a concentration test: significant when above 100 lb/day and the ambient increase is 5.0 micrograms per cubic meter or more (1.0 in a Class I area).
• NO2, SO2, CO, lead. Exceeding the screening level requires modeling against the state and national standards rather than a finding.
• CO hotspots. Analysis required for receptors within 500 feet of a signalized intersection at level of service E or worse with more than 3,000 peak hour trips, or for a project that causes such an intersection.
• Toxics. The Rule 1200 framework: incremental cancer risk above 1 in a million without toxics best available control technology, above 10 in a million with it, or a hazard index above 1.
• Odor. Qualitative, under the district's Rule 51 nuisance rule and the Health and Safety Code.
• Greenhouse gases. Not addressed in this document.

City of San Diego, September 2022 thresholds

The City's CEQA Significance Determination Thresholds, September 2022, reprint the Rule 20.2 trigger levels as Table A-2 and say plainly that the district did not set them for CEQA or for mobile sources; a 2002 court ruling means they cannot be the sole basis for a finding, so the City applies them as a screening tool alongside other evidence.

Pollutant	lb/hr	lb/day	tons/yr
CO	100	550	100
NOx	25	250	40
PM10	None	100	15
SOx	25	250	40
Lead	None	3.2	0.6
PM2.5	None	None	None
VOC	None	137	15

• Dust. The initial study asks whether the project exceeds 100 lb/day of particulate matter. The City's rule of thumb is 26.4 pounds of PM10 per graded acre, so grading about four acres a day reaches 100 pounds; watering once cuts it roughly in half and twice by three quarters.
• CO hotspots. Screening with EMFAC emission factors and, where needed, CALINE-4; triggers include a six or four lane road dropping to level of service E or worse and sensitive receptors within 400 feet where service is worse than D.
• Odor. In the City's words, siting receptors near an existing odor source is significant when the project site is closer to the source than any existing sensitive receptor where there has been more than one confirmed or three confirmed complaints per year, averaged over a three week period.
• VOC differs by jurisdiction. The County's Table 5 carries 75 lb/day and 13.7 tons per year; the City's Table A-2 carries 137 lb/day and 15 tons per year. Same pollutant, same basin, different number depending on the lead agency.
• Greenhouse gases. No tonnage threshold. A project is less than significant when (a) it is consistent with the General Plan and Community Plan land use and zoning, or its amendment increases density within a Transit Priority Area, or its amendment is equivalent or less GHG intensive, and (b) it complies with the Climate Action Plan Consistency Regulations in San Diego Municipal Code sections 143.1410 and 143.1415. Any project that fails either step prepares a comprehensive project-specific GHG analysis and is significant if inconsistent with the Climate Action Plan, updated August 2, 2022 with a net zero target for 2035.

What this means for a report

Three authorities, one basin. A County project cites the 2007 guidelines and Table 5. A City project cites the 2022 thresholds and the Climate Action Plan regulations. A project in another city in the county cites that city's practice, which usually leans on one of the two. The district's own 2024 document is cited for process, not numbers.

Where the thresholds are published

San Diego County Air Pollution Control District, Environmental Review Guidelines: Procedures for Implementing the California Environmental Quality Act, November 14, 2024; County of San Diego, Guidelines for Determining Significance and Report Format and Content Requirements, Air Quality, March 19, 2007 (Table 5 and Sections 4.2 through 4.5); City of San Diego, California Environmental Quality Act Significance Determination Thresholds, September 2022 (Section B Air Quality and Odor, Table A-2; Section T Greenhouse Gas Emissions); San Diego County Air Pollution Control District Regulation II, Rule 20.2, Table 20-2-1.