Responses of Photochemical Air Pollution in California’s San Joaquin Valley to Spatially and Temporally Resolved Changes in Precursor Emissions

Abstract

Ground-level ozone adversely affects human health and ecosystems. The effectiveness of control programs depends on which precursor(s) are controlled, by how much, and where and when emission reductions occur. We use the adjoint of the Community Multiscale Air Quality model to investigate odd oxygen (O x ≡ O3 + NO2) sensitivities in California’s San Joaquin Valley (SJV) to precursor emissions from local and upwind sources. Sensitivities are mapped and disaggregated by hour and day. Taken together, impacts of precursor emissions in the San Francisco Bay area and Sacramento Valley are similar in magnitude to impacts of local SJV emissions. Same-day emission sensitivities are mostly attributable to local sources, with the most influential anthropogenic emissions of VOCs (volatile organic compounds) and NO x (nitrogen oxides) occurring in the morning (9–11 am) and early afternoon hours (1–3 pm), respectively. For the northernmost SJV receptor, the influence from Sacramento Valley emissions peaks 5–6 h later than Bay area emissions; this difference diminishes for SJV receptors located further downwind. Results show a shift toward more NO x -sensitive conditions in the afternoon with all but the southernmost receptor shifting from VOC- to NO x -sensitive conditions. We also evaluate opportunities to control pollution through shifts in precursor emission location and timing.

Location-Specific Control of Precursor Emissions to Mitigate Photochemical Air Pollution

“…Previous studies have identified two upwind air basins, the SV and the SF Bay, as important contributors to O x concentrations in the SJV. These upwind contributions arise mostly from prior-day rather than same-day precursor emissions , and include combined effects from transport of precursors emitted and ozone formed in the upwind areas.…”

“…All simulations are conducted for a standard set of meteorological conditions, representing a weeklong period (27 July to 2 August 2000) that is selected based on results of a cluster analysis . This time period has been the focus of multiple modeling and measurement studies ,− and is representative of a recurring ozone-inducing meteorological regime . Its flow patterns are close to the summer average (Figure S1) with prevailing high temperatures (Figure S2).…”

“…This study uses the adjoint method to quantify separate impacts of emission changes at each possible location within the study domain whether or not existing sources are present. Our approach is complementary to prior studies that quantify impacts of proportional reductions in existing emissions at all source locations. , The present study features high spatial resolution (4 km) to resolve source locations that may exhibit sharp spatial gradients in their air quality impacts.…”

“…Examples of location-specific control measures include electrification of local school and transit bus fleets, trash haulers, and parcel delivery vehicles; accelerated replacement of household natural gas appliances with electric models; electrification of freight-handling facilities (e.g., ports, rail yards, warehouses, and associated highway/rail corridors); and rollout of electric vehicle (EV) charging infrastructure and other incentives to encourage EV adoption. Such location-specific measures may also be aligned with parallel efforts to improve conditions in communities that are disproportionately vulnerable to and adversely affected by air pollution. , …”

“…Our approach is complementary to prior studies that quantify impacts of proportional reductions in existing emissions at all source locations. 10,11 The present study features high spatial resolution (4 km) to resolve source locations that may exhibit sharp spatial gradients in their air quality impacts.…”