The six questions every CEQA air analysis answers
Appendix G of the State CEQA Guidelines is the environmental checklist lead agencies use for an initial study. Its Air Quality section asks four questions and its Greenhouse Gas Emissions section asks two. Every air quality and GHG technical report in California is organized to answer these six, and each answer is one of four findings: no impact, less than significant, less than significant with mitigation, or potentially significant. The district thresholds decide two of the six almost mechanically: the criteria pollutant question and, where the district has a numeric path, the GHG generation question. The other four turn on plan consistency, receptor exposure, odor, and climate policy, and they need a professional's judgment on the evidence.
Air quality
(a) Conflict with or obstruct implementation of the applicable air quality plan?
The plan is the district's clean air plan or attainment plan. The Bay Area's guidance sets a three-part test, all parts answered yes with evidence: does the project support the plan's primary goals, does it include every applicable control measure, and does it avoid disrupting or hindering any control measure (a project that precludes a planned transit extension is the guidance's example of hindering one). South Coast and San Diego practice test growth consistency instead: the plan's emission forecasts rest on the general plans, so a project at or below its planned density and land use is within the plan's assumptions, and one that adds population or trips beyond them may not be. Many reports also treat an exceedance of a mass threshold as inconsistent with the plan's goals; that is common practice, not a district rule. Evidence: the plan in force and its control measures, the general plan designation and zoning, and the project's units and floor area against them.
(b) Result in a cumulatively considerable net increase of any criteria pollutant for which the project region is non-attainment under an applicable federal or state ambient air quality standard?
This is the threshold question. The project's construction and operational emissions of the non-attainment pollutants and their precursors, ROG or VOC, NOx, PM10, and PM2.5, are compared to the district's thresholds. In the Bay Area, South Coast, San Joaquin Valley, and Sacramento an exceedance is a significant impact, and a mitigated model run shows whether adopted measures bring it under. San Diego lead agencies borrow the district's permit trigger levels as screening: the County treats ozone precursor and PM exceedances as significant but sends NO2, SO2, CO, and lead exceedances to ambient modeling, and the City weighs its Table A-2 values with other evidence rather than as the sole basis for a finding. The comparison method differs by district (see the district pages): average daily by construction year in the Bay Area, daily maximum in South Coast, tons per year in San Joaquin Valley. The Bay Area adds a condition for construction dust: every basic best management practice must be committed, or the dust impact is not less than significant regardless of the numbers. A finding below the thresholds is a less than significant contribution, not a finding that the project has no emissions; the cumulative framing is the point of the question.
(c) Expose sensitive receptors to substantial pollutant concentrations?
Sensitive receptors are people most affected by poor air quality, in the usual list children, the elderly, and people with existing illness, at homes, schools, daycare, hospitals, and parks. The question covers three things: toxic air contaminants, chiefly diesel particulate from construction equipment and truck traffic, measured as excess cancer risk and hazard index at the nearest receptor; localized criteria pollutant concentrations, by South Coast look-up table or dispersion model; and carbon monoxide hotspots at congested intersections, screened by traffic volume or level of service. Districts set the numbers: 10 in a million cancer risk in the Bay Area and South Coast; 20 in San Joaquin Valley on its July 2015 sheet (the March 2015 GAMAQI text prints 10); Sacramento for stationary sources only; San Diego County 1 in a million without toxics best available control technology and 10 with it. A health risk assessment answers this question when construction runs long, when receptors are close, or when the project brings new residents next to a freeway or a permitted source.
(d) Result in other emissions (such as those leading to odors) adversely affecting a substantial number of people?
Two situations: a project that generates odors sited near receptors, or a project that brings receptors near an existing odor source. Evidence is the facility type against the district's screening distances, the complaint history at the district's compliance office, and the nuisance rule. Bay Area and San Joaquin Valley publish complaint-count tests and distance tables; South Coast and Sacramento rely on their nuisance rules, each numbered Rule 402; the City of San Diego has its own complaint test. Most residential and office projects answer this with a short qualitative discussion.
Greenhouse gas emissions
(a) Generate greenhouse gas emissions, either directly or indirectly, that may have a significant impact on the environment?
The answer depends entirely on which district's path applies. In the Bay Area, the project either includes every design element in Table 3-2 (no natural gas; no wasteful energy use; VMT 15 percent below the regional average per capita for residential and per employee for office, no net increase for retail, or an adopted SB 743 target; CALGreen Tier 2 EV readiness) or shows consistency with a qualified local GHG reduction strategy; the tonnage is disclosed but not compared to a number. In Sacramento, construction is compared to 1,100 metric tons per year and operations go through tier 1 and tier 2 practices. In San Joaquin Valley, compliance with an approved GHG reduction plan, Best Performance Standards, or a 29 percent reduction below business as usual. In South Coast, no adopted land use threshold, so the lead agency states its own. In the City of San Diego, both steps of its test: land use consistency with the General Plan and Community Plan (or a qualifying amendment) and compliance with the Climate Action Plan Consistency Regulations in Municipal Code sections 143.1410 and 143.1415. Where a path quantifies, the CalEEMod annual GHG total in metric tons CO2e is the disclosed quantity; San Joaquin Valley's plan-compliance and Best Performance Standards paths require no quantification at all. Construction GHG is reported as a total over the build, and South Coast practice amortizes it over a 30 year project life and adds it to operations.
(b) Conflict with an applicable plan, policy or regulation adopted for the purpose of reducing the emissions of greenhouse gases?
The plans are the CARB Scoping Plan, the regional Sustainable Communities Strategy, and any local climate action plan. In the Bay Area and Sacramento a project that meets the district's GHG path is usually found consistent with all three, since those paths are built from the current Scoping Plan's measures. San Joaquin Valley's 2009 method predates the current state targets, so a project that passes it still assesses consistency with the Scoping Plan, the Sustainable Communities Strategy, and any local climate plan on their own terms. Where a local plan has a project-level checklist, as the City of San Diego's Climate Action Plan does, the checklist is filled in and attached. Inconsistency with an adopted plan is a significant impact on its own, independent of tonnage.
Which answers are decided by the numbers
| Question | Decided by | What a professional still has to judge |
|---|---|---|
| Air (a) plan consistency | Judgment | Whether the project's growth is within the general plan the air plan assumed |
| Air (b) criteria pollutants | Threshold comparison | Whether the model inputs match the project, and which mitigation is enforceable |
| Air (c) receptors | Judgment, against the district's risk numbers where a risk assessment or localized analysis exists | Whether the analysis was needed at all, and receptor distances |
| Air (d) odor | Judgment, with district screening tools | Facility type, distance, complaint history |
| GHG (a) generation | Threshold or checklist comparison, path by district | Whether each design element or practice is actually in the project's conditions |
| GHG (b) plan conflict | Judgment | Which plans apply and whether their measures bind the project |
Where the questions are published
State CEQA Guidelines, Appendix G, Environmental Checklist Form, sections III (Air Quality) and VIII (Greenhouse Gas Emissions), current wording as printed in initial studies since the 2018 Guidelines update. District treatment of each question: Bay Area 2022 CEQA Air Quality Guidelines, Chapters 3, 5, and 6; San Joaquin Valley GAMAQI (March 2015), Chapter 8; South Coast Air Quality Significance Thresholds (March 2023); Sacramento CEQA Guide, Chapters 2 through 7; City of San Diego CEQA Significance Determination Thresholds (September 2022), Sections B and T.