Air Quality Trends

The Sac Metro Air District evaluates the air quality data and tracks the Sacramento region's progress towards meeting federal and state air quality standards. Below are the air quality and emission trends for the two pollutants of most concern in the region – fine particulate matter (PM_2.5) and ozone (O₃). These trends show how air quality has improved since 2000. Information on other air quality pollutants can be found on the Air Quality Pollutants and Standards Page (link).

Ambient Concentration Trends

Ozone Concentrations

A design value is used to compare the ambient concentrations to the air quality standard. For ozone, the design value is calculated by taking the average of the 4^th highest annual 8-hour ozone concentration over three consecutive years. Ozone concentrations are usually highest in the summer. The figure below shows the peak 8-hour ozone design values from 2000 – 2022 in the Sacramento region.

O3 Trend 2000-22a.png

Particulate Matter Concentrations

Particulate Matter – 2.5 microns or less (PM_2.5)

For particulate matter for 2.5 microns or less, the design value is calculated using the 3-year average of the 98th percentile of 24-hour PM_2.5concentrations. The figure below shows the PM_2.5concentrations from 2000 to 2021. For federal air quality planning purposes, the figure excludes unusually high fine particulate matter concentrations in 2018 and 2020 due to wildfire smoke impacts. The region has made significant progress in reducing ambient PM_2.5concentrations since 2007, after implementation of the District's wood burning prohibition rule also known as the "Check Before You Burn" program. PM_2.5concentrations are normally higher during the winter months in Sacramento due to the increase in residential wood burning activities (except during wildfire events). Excluding wildfire impacted days, concentrations have remained at or below the federal standard since 2013.

PM DV Scn2b.png

Emissions and Precursors Trends

Ozone precursors

Ozone is not directly emitted from emission sources. It is a product of complex photochemical reactions and involves two precursors: volatile organic compounds (VOC) and oxides of nitrogen (NO_X). To evaluate ozone, the District evaluates the emissions of VOC and NO_X. The emissions inventory graphs show the VOC and NO_X trends from 2000 to 2032 (forecasted) during the summer months (May through October). Summer is typically when ozone concentrations are the highest. The emission trends show significant declines in emissions, despite increasing population, vehicle activity, and economic development. The drop in ozone precursors corresponds to a decrease in ozone concentrations.

SFNA VOC Ems Inv v2.png Data source CEPAM: 2019 SIP Baseline Emission Projections, Emission Projections with External Adjustments, Sacramento NAA 2019 Ozone SIP Version 1.04

Fine Particulate Matter and Precursors

Fine particular matter can be emitted directly or formed by chemical reactions of precursors - nitrogen oxide (NO_X), sulfur dioxide (SO₂), volatile organic compounds (VOCs), and ammonia (NH₃). This figure shows how much precursor emissions have decreased since 2005, and the emissions are expected to continue to decrease in the future despite an increase in population and economic growth. SFNA PM25 Ems Inv v2.png

Data Source: CEPAM: NORCAL 2012 PM_2.5 SIP Baseline Emission Projections, Section a1 – Emission Projections with External Adjustments, Sacramento Nonattainment Area 2012 PM_2.5 SIP Version 1.01.

Composition of the PM_2.5 and precursor NO_X emissions in Sacramento County

The pie charts below show the 2024 emissions source category of direct PM_2.5 emissions and precursor NO_X emissions in Sacramento County. NO_X reacts with ammonia and water moisture in the air to form secondary particulate matter. Residential Wood burning is the major source of direct PM_2.5 emissions and mobile sources emissions are major components of NO_X emissions in Sacramento County.

Pie Chart 2024 Avg Annual PM25 for Sac Cty - PM25.png

Pie Chart 2024 Avg Annual PM25 for Sac Cty - NOX.png

Data Source: NORCAL 2012 PM_2.5 SIP Baseline Emission Projections, Section a1 – Emission Projections with External Adjustments, Sacramento Nonattainment Area 2012 PM_2.5 SIP Version 1.01.