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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 (PM2.5) 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 4th 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 (PM2.5)

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 PM2.5 concentrations. The figure below shows the PM2.5 concentrations 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 PM2.5 concentrations since 2007, after implementation of the District's wood burning prohibition rule also known as the "Check Before You Burn" program. PM2.5 concentrations 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 (NOX). To evaluate ozone, the District evaluates the emissions of VOC and NOX. The emissions inventory graphs show the VOC and NOX 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 NOX Ems Inv v2.png

SFNA VOC Ems Inv v2.pngData 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 (NOX), 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 PM2.5 SIP Baseline Emission Projections, Section a1 – Emission Projections with External Adjustments, Sacramento Nonattainment Area 2012 PM2.5 SIP Version 1.01.
Composition of the PM2.5 and precursor NOX emissions in Sacramento County
The pie charts below show the 2024 emissions source category of direct PM2.5 emissions and precursor NOX emissions in Sacramento County. NOX reacts with ammonia and water moisture in the air to form secondary particulate matter. Residential Wood burning is the major source of direct PM2.5 emissions and mobile sources emissions are major components of NOX emissions in Sacramento County.

Pie Chart 2024 Avg Annual PM25 for Sac Cty - PM25.pngPie Chart 2024 Avg Annual PM25 for Sac Cty - NOX.png
Data Source: NORCAL 2012 PM2.5 SIP Baseline Emission Projections, Section a1 – Emission Projections with External Adjustments, Sacramento Nonattainment Area 2012 PM2.5 SIP Version 1.01.

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