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AQI & Your Health

AQI Quick Guide - Where to get the best info to protect my health

Laws like the “General Industry Safety Orders, Chapter 4, Subchapter 7, Section 5141.1” for outdoor worker protection from wildfire smoke require employers to check AQI forecasts and the current AQI for PM2.5 from either the US EPA AirNow website, CARB website or local air pollution control district website. At SLO County APCD, we use a combination of methods to provide the most accurate current and forecasted AQI values to help you make the best decisions to protect your health, the health of your families, and your employees.

What Pollutants are Regulated?

The AQI is calculated for the five major air pollutants regulated by the Clean Air Act: ozone, particle pollution (also known as particulate matter, PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, US EPA has established national air quality standards to protect public health. If multiple pollutants are monitored in the same area (Like PM and ozone in many of the SLO County locations), then overall AQI for the area is reported as the highest of the individual pollutant AQIs. For example, if the ozone AQI is 35 and the PM2.5 is 52, then the overall AQI for the area is 52. Ozone and particulate matter are the two pollutants that pose the greatest threat to human health in general.

Forecast vs Monitors vs Sensors

Newer monitors can measure air pollution on much shorter timescales (a few seconds to an hour), however, the official AQI is still tied to the longer averages, i.e. 24-hour averages for particulate matter and 8-hour averages for ozone. The US EPA has developed the NowCast AQI to bridge the gap between the official AQI scale, which is based on 8-hour or 24-hour measurements, and short-term, hourly pollutant values that are reported in real-time. This method takes recently measured pollutant values and tries to forecast an 8-hour or 24-hour average. It then converts this value to the AQI using the standard 8-hour or 24-hour AQI scale. The “Current Air Quality Conditions” that appear on the APCD website and airnow.gov are NowCast AQI values.

The APCD provides a 6-day forecast, updated daily. The forecast reports the official, daily AQI, and even though the forecast may say the AQI levels are forecasted to be yellow, there may be periods when the NowCast AQI is in the green, orange or red because the reporting is more instantaneous. An explanation of this is always available on our forecast page under the “Air Quality Forecast Discussion” section.

There are also commercial, non-EPA-approved sensors available on the internet for the general public. Although many of these third-party sensors, like PurpleAir.com, are good indicators of PM2.5 air pollution levels, they report short-term (less than one-minute) measurements using the 24-hour AQI scale. Reporting instantaneous values in this fashion can over and underestimate the health impacts.

For more details, visit: https://www.airnow.gov/index.cfm?action=aqibasics.aqi

At times, the AQI for the Nipomo Mesa can be reported as Unhealthy, Very Unhealthy or Hazardous, but the 24-hour AQI, on which PM health standards are based, is Moderate.  It is important to take action to protect your health during any periods that are reported as Unhealthy or worse, but keep in mind that the health effects would be considered Unhealthy only if it were at the Unhealthy level for a 24-hour period.

Health Impacts of Air Pollution

Air pollution can cause or contribute to serious health impacts for people of all ages, including pulmonary, cardiac, vascular, and neurological impairments. Ozone and particulate matter have specifically been known to cause irritation to the respiratory system, reduced lung function, damage to the cells that line the lungs, as well as permanent lung damage. Air pollution can also trigger heart attacks, strokes, and irregular heart rhythms, especially in people who are already at risk for these conditions.

According to the California Air Resources Board, air monitoring shows that over 90 percent of Californians breathe unhealthy levels of one or more air pollutants during some part of the year. Asthma attacks have been linked to poor air quality. In 2014, 13.8% of adults reported that they had been diagnosed with asthma at some point in their life. Among children under 18, 13.7 % had asthma. This translates to approximately 4 million adults and 1.2 million children in California that have been diagnosed with asthma.

Many different kinds of air pollutants are released into the atmosphere and are captured in our lungs with every breath we take. Each of these pollutants affect our body in a specific way and each can cause serious health problems depending on pollutant levels and the exposed individual. Click on any of the pollutants below for explanations of some of the main outdoor pollutants, where they come from, how they impact our bodies, and ways we can reduce that pollution!

Protect Your Health & Indoor Air Quality

Air Quality Recommendation Sheet for Schools

Awareness is the key to protecting your health! The SLO County APCD provides current and forecasted air quality information so you can stay informed. If you notice air pollution levels are elevated in your area, limit your time outdoors and avoid outdoor exercise. It’s also best to keep your windows closed and run your AC on recirculate, if available, with a clean filter. Click here to learn more about the EPA's "Clean Room Tips." We also have developed a helpful poster for how to create a "Clean Room" in your home, click here to download!

People with heart or lung issues should be especially careful when the hourly NowCast AQI starts to reach yellow (moderate, 50 to 100) and orange (unhealthy for sensitive groups, 100 to 150) levels. These levels typically mean that air quality has deteriorated and those who are especially sensitive may begin to experience health effects. If the AQI goes into the orange or red levels, and you are a sensitive individual, stay indoors or go to a location with lower AQI values, if necessary. Always consult your physician if you are experiencing health problems.

You can also stay up to date on significant air quality events by signing up for our AirAware text notification system. We send messages right to your phone for a variety of notifications, like early blowing dust events, unhealthy air quality and more. The more awareness you have, the better health-based decisions you can make.

EPA Lowers Fine Particulate Matter Threshold

The Environmental Protection Agency (EPA) periodically evaluates the National Ambient Air Quality Standards (NAAQS) to ensure the protection of public health and the environment. As of May 6, 2024, in pursuit of heightened health protection, the EPA has taken the decision to revise downward the Ambient Air Quality Standard, following a thorough examination of available scientific data.

Although the color scale of the Air Quality Index (AQI) remains consistent, the thresholds defining each category have been adjusted. What does this mean for us here in San Luis Obispo County? Residents of SLO County may observe an increase in the number of days categorized as Moderate, even in instances where overall air quality remains relatively stable or unchanged. Rough analysis of data from the preceding three years suggests an anticipated rise of approximately 10% in Moderate category occurrences under the new criteria.

It is essential to note that these adjustments do not alter the actions we undertake in response to air quality challenges. We remain committed to providing ongoing updates and information regarding local air quality conditions. For more information on this, feel free to read through any of the helpful links below. 



What is the AQI?

The Air Quality Index or AQI is a health-based scale for reporting daily air quality and is an indicator of how clean or polluted the air is. The higher the AQI value, the greater the level of pollution and the greater the health concern. When the AQI is in the green or ”good” range (0 to 50), air quality is considered satisfactory and poses little to no risk. However, as AQI gets into the orange, “unhealthy for sensitive groups” range (100 to 150), sensitive groups (children, elderly, pregnant women and those with existing heart and lung conditions) may begin to experience health effects. The higher the AQI, the more of the population could begin to experience health effects. The more sensitive you may be, the sooner you may notice adverse effects.

Looking for info on South County/Nipomo Mesa Air Quality? Click here!

Why is the AQI Important?

The AQI focuses on the health effects one may experience within a few minutes, a few hours or days after breathing polluted air. Studies that the US EPA used to determine these health effects evaluated long exposures: 24 hours for particulate matter and 8 hours for ozone. Therefore, the official AQI for a day in the past and the AQI forecasts for future days are based on these time periods.