Air Quality Trends

The Sac Metro Air District evaluates trends in air quality concentrations and emission inventories to monitor progress towards meeting federal and state air quality standards.

Concentration Trends

Ozone

The 8-hour ozone (O₃) peak design value (an average of the 4^th highest ozone concentration over three years) is the highest design value at any site in the Sacramento Federal Nonattainment Area (SFNA) and is compared against current and past ozone standards to determine attainment. Meteorology plays an important role in ozone formation and the variability in design value concentrations. For more information regarding ozone trends, please see the 2008 NAAQS Ozone Attainment Plan. Ozone concentrations are usually highest in the summer when it is hot and when there are light winds.

Sources: 1990-2020 Design Values were extracted from AQS Report (AMP 480) downloaded on 12/22/2021. The design values are based on 2015 National Ambient Air Quality Standard.
Preliminary 2021 Design Values were calculated based on the CARB AQMIS downloaded on 02/16/2022.
Notes:

1) A Design Value is a 3 year average of 4th highest ambient ozone concentration at a monitor.

2) The SFNA was impacted by wildfires in 2016, 2018, 2020, and 2021, which caused unusually high ozone concentrations. The peak design value calculation in this chart excluded the high ozone readings due to wildfires.

Particulate Matter

The region has made significant progress in reducing ambient PM_2.5concentrations since 2007, after implementation of wood burning controls. AQ Trendlines - PM2.5.jpg

Data source: 2000-2021 Deisgn Values were extracted from AQS Report (AMP 480) downloaded on 07/28/2022. Data in 2021 has not yet been certified.

Notes:
1) The SFNA-PM2.5 was impacted by several major wildifres in 2018, 2020, and 2021, which causes unusual high ambinet PM2.5 concentration. The peak design value in this chart excluded the days with high ambient concentrations in 2018, 2020, and 2021.

Emission Trends

Emissions of precursors for both ozone and particulate matter have decreased steadily in the Sacramento region due to implementation of local, state, and federal emission control programs.

Ozone precursors

The precursors associated with ozone are volatile organic compounds (VOC) and oxides of nitrogen (NOx). The emissions inventory graphs show the VOC and NO_X trends 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 largest reduction in emissions was from on-road motor vehicles, where there was a 66% reduction for VOCs and 62% for NOx from 2000 to 2015. The drop in NOx and VOC emissions corresponds to attainment of the 1979 1-Hour Standard in 2009 (attainment was based on data from 2007 – 2009).

Data source: CEPAM: 2016 SIP Baseline Emission Projections, Section a1 – Emission Projections With External Adjustments, Sacramento NAA 2016 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 are expected to continue to decrease in the future despite an increase in population and economic growth.

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.