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The words in an air quality and GHG report

Short definitions of the terms that recur in California CEQA air quality and greenhouse gas analyses, in the sense the district guidance documents use them.

Pollutants and units

  • Criteria pollutants. The pollutants with ambient air quality standards: ozone, particulate matter (PM10 and PM2.5), carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. California adds sulfates, hydrogen sulfide, vinyl chloride, and visibility reducing particles.
  • Precursors. Pollutants that form another pollutant in the air. ROG and NOx are ozone precursors; NOx and SOx also form secondary particulates. Thresholds are written for precursors because ozone itself is not emitted.
  • ROG and VOC. Reactive organic gases and volatile organic compounds, near-synonyms for the organic ozone precursors. CARB and the Bay Area say ROG; EPA and South Coast say VOC.
  • NOx. Oxides of nitrogen, mainly from combustion in engines and boilers. The precursor most often driving a construction exceedance.
  • PM10 and PM2.5. Particulate matter of 10 and 2.5 micrometers or less. Reported as exhaust (combustion), fugitive dust (earthmoving, unpaved roads), and total. Which of the three a threshold compares differs by district.
  • CO2e. Carbon dioxide equivalent: all greenhouse gases weighted by global warming potential and expressed as CO2. Reported in metric tons per year, written MT, MTCO2e, or tCO2e.
  • lb/day and tons/yr. Pounds per day and tons per year, the two mass bases for criteria pollutant thresholds. One ton is 2,000 pounds; 10 tons per year over 365 days is about 54.8 pounds per day.
  • Micrograms per cubic meter and ppm. Concentration units for ambient standards and localized analyses, as opposed to mass emission rates.

Analysis terms

  • Threshold of significance. The level at which a lead agency treats an impact as significant under CEQA Guidelines 15064.7. Districts recommend them; lead agencies adopt them.
  • Non-attainment. A region that does not meet an ambient standard for a pollutant. Appendix G question (b) asks only about pollutants the region is in non-attainment for, which is why the Bay Area and Sacramento set no SOx or CO mass threshold.
  • Maximum daily, average daily, annual. The three time bases CalEEMod prints. The Bay Area's construction rate is computed from the annual row over that year's working days, not read from the model's average daily row; operational average daily is annual tons over 365, or over the actual operating days for an intermittent use such as a school or arena.
  • Working days. The days construction actually occurs in a calendar year, from the phase schedule and days per week. The divisor for the Bay Area's construction average daily rate.
  • Unmitigated and mitigated. Two model runs: the project as proposed, and the project with reduction measures applied. Which measures belong in which run is a district convention, and the Bay Area's required twice-daily watering sits in the unmitigated run.
  • Overlap year. A year in which construction continues while part of the project operates. The Bay Area combines construction exhaust with operational emissions for that year.
  • Localized significance threshold (LST). South Coast's voluntary look-up table method for a project's on-site effect on nearby receptors, by source receptor area, site acreage, and receptor distance.
  • Screening level. A project size below which a district presumes emissions are under its thresholds, so no quantification is required: Bay Area Table 4-1, San Joaquin Valley SPAL, Sacramento's operational screening table.
  • Ambient air quality analysis (AAQA). Dispersion modeling of a project's emissions against the ambient standards. San Joaquin Valley recommends it when on-site emissions of any pollutant remain above 100 pounds per day after enforceable mitigation.
  • CO hotspot. A localized carbon monoxide concentration at a congested intersection. Screened by traffic volume in the Bay Area, by level of service in San Joaquin Valley, and by level of service plus a 3,000 peak hour trip test in San Diego County.
  • Sensitive receptors. People most susceptible to air pollution and the places they gather: homes, schools, daycare centers, hospitals, nursing homes, parks.
  • Toxic air contaminants (TACs). Pollutants with health effects at low concentrations, chiefly diesel particulate matter in a development project. Measured as excess cancer risk per million and hazard index.
  • Health risk assessment (HRA). Dispersion modeling plus exposure calculation for TACs at the maximally exposed receptor, usually with the AERMOD dispersion model.
  • Hazard index. The ratio of a modeled TAC concentration to its reference exposure level, summed by organ system; chronic and acute versions. A value of 1 is the usual threshold.
  • Cancer burden. The number of excess cancer cases expected in the exposed population; South Coast uses 0.5 cases where risk is at or above one in a million.
  • Cumulative. The project's contribution together with other past, present, and foreseeable projects. The Bay Area's 1,000-foot radius test for risks and hazards is a cumulative threshold.

Mitigation and design terms

  • Best management practices (BMPs). Construction dust and exhaust controls, treated differently by district: the Bay Area's nine basic practices in Table 5-2 are the condition of a less than significant dust finding; Sacramento's list unlocks its non-zero PM thresholds; San Joaquin Valley treats its dust rules as compliance, not mitigation.
  • Enhanced measures. Controls beyond the basic practices, for sites near receptors or exceeding thresholds.
  • Tier 4 Final. The strictest EPA emission tier for off-road diesel engines. Requiring Tier 4 Final equipment is the usual construction NOx and PM mitigation, entered in CalEEMod as an equipment tier.
  • Rule 403 (South Coast), Regulation VIII (San Joaquin Valley), Regulation 6 (Bay Area). District particulate and fugitive dust rules that apply by law. San Joaquin Valley says compliance with Regulation VIII is not mitigation because the law already requires it; the Bay Area makes its Table 5-2 practices, which overlap Regulation 6, the condition of the dust finding.
  • Indirect Source Review, Rule 9510. San Joaquin Valley's requirement that development projects reduce construction and operational NOx and PM10 through design or off-site fees.
  • Design elements. The Bay Area's Table 3-2 features that make a land use project's GHG contribution less than significant: no natural gas, no wasteful energy use, VMT reduction, CALGreen Tier 2 EV readiness.
  • Qualified GHG reduction strategy. A local climate action plan meeting CEQA Guidelines 15183.5(b): quantified inventory, a significance level, measures, monitoring, and adoption after environmental review. Consistency with it is the alternative GHG path in the Bay Area and the City of San Diego.
  • Best Performance Standards (BPS). San Joaquin Valley's adopted list of GHG-reducing design elements and technologies; projects that implement them need not quantify GHG emissions.
  • Business as usual (BAU). The emissions a project would have without reduction measures, the baseline for San Joaquin Valley's 29 percent test.
  • VMT. Vehicle miles traveled. SB 743 made it the CEQA transportation metric. The Bay Area's design elements require a 15 percent reduction per capita or per employee, or a locally adopted SB 743 target; Sacramento requires the same 15 percent only for projects still above 1,100 metric tons after its tier 1 practices.
  • CALGreen Tier 2. The voluntary higher tier of the California Green Building Standards Code. Its electric vehicle parking requirements are a GHG design element in the Bay Area and Sacramento.

Documents and agencies

  • Appendix G. The State CEQA Guidelines environmental checklist; its four air quality and two GHG questions structure every report.
  • Initial Study, ND, MND, EIR. The CEQA documents: an initial study leads to a negative declaration, a mitigated negative declaration, or an environmental impact report. The air quality technical report is an appendix to one of them.
  • Lead agency. The public agency approving the project and making the significance findings, usually a city or county. Districts recommend; lead agencies decide.
  • Air district. One of California's 35 regional air pollution control or air quality management districts. The five largest by CEQA volume have pages in this section.
  • CARB. The California Air Resources Board, which sets state ambient standards, writes the Scoping Plan, and maintains the EMFAC and OFFROAD emission factor models inside CalEEMod.
  • Scoping Plan. CARB's plan for meeting the state's GHG targets under AB 32, SB 32, and AB 1279: 40 percent below 1990 by 2030 and carbon neutrality by 2045.
  • Sustainable Communities Strategy. The regional land use and transportation plan under SB 375 that a GHG plan-consistency finding cites, for example Plan Bay Area.
  • Clean air plan. The district's attainment plan, the "applicable air quality plan" in Appendix G question (a).
  • Statement of overriding considerations. The lead agency's finding, under CEQA Guidelines 15093, that a project's benefits outweigh a significant and unavoidable impact. Required only when the agency approves a project despite such an impact; denying the project needs none.