ARB Frequently Asked Questions

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General Air QualityAir Quality IndicatorsResources
What are the health effects of air pollutants?

Health effects from Particulate Matter (PM) can include respiratory disease, lung damage, cancer, and increased mortality. Health effects from ozone can include breathing problems, lung tissue damage, and premature mortality. Higher levels of toxic compounds can lead to chronic health problems such as cancer.

More information on Health Effects of Air Pollution[Internal] is available online.

What are the air quality standards for California?

Air quality standards are the definition of clean air. They cover a number of known pollutants that scientific studies have shown to cause adverse health impacts. Air quality standards are set by both the U.S. EPA[External]and the ARB[Internal]. The standards are periodically reviewed and revised as appropriate to ensure they protect the health and welfare of every Californian.

What is the difference between Air Quality and Emissions Inventory information?

Air quality information is based on measured data and provides information about the concentrations of pollutants in the outdoor air. It also provides information on public exposure, the extent of air quality problems, and whether air quality complies with federal and State standards. Air quality data do not provide direct information on how different sources of pollution contribute to the measured concentrations.

In contrast, emissions inventory information reflects estimates of the amount of pollutants, either gases or particles, emitted into the atmosphere by different types of sources. This information can be used to identify sources with high emissions that may impact the public, inform regulatory actions, and evaluate the effectiveness of control measures. However, emissions inventory information gives no indication of what happens in the atmosphere, how far emissions travel, or which areas they impact.

How can I tell what the air quality is around California?

A number of tools are available on ARBís website to help you locate information on air quality concentrations throughout California.

iADAM[Internal] (Aerometric Data Analysis and Management) gives you access to ADAM, Californiaís repository for official air quality data and statistics. iADAMís information includes the statistics needed for regulatory air quality evaluation (to determine whether or not an area meets ambient air quality standards, for example), as well as other commonly used air quality metrics, such as number of days over a standard and peak concentrations for criteria pollutants, and annual averages and risk numbers for toxics compounds. iADAMís information goes as far back as 1963 in some instances, and includes all data through the most current regulatory year (usually the year before the current year).

AQMIS[Internal] (Air Quality and Meteorological Information System) shows you what is happening today based on near real-time data (last hour or so) based on data extracted directly from Californiaís extensive air quality and meteorology monitoring networks. These data, while preliminary and not yet official, can tell you what air quality is like today. AQMIS also combines its preliminary data with ADAMís official data into summaries that give you an up-to-date view of this yearís air quality and allows you to compare that information to air quality data from previous years.

What are the sources of emissions in California?

Pollutant emissions come from a variety of sources, including motor vehicles, industrial facilities, ships, trains, and area-wide sources. Estimates of the emissions from all sources are compiled in the Emissions Inventory[Internal] database. The database includes not only estimates of current emissions, but also estimates of emissions for previous years and future years. The future year estimates are based on expectations of future economic and population growth, as well as emission controls. This data can be helpful in determining the types of sources and pollutants that are present in a particular area.

What are toxics compounds?

Toxic compounds are compounds that are suspected to cause chronic, negative health impacts, such as cancer. Examples of toxic compounds include diesel particulate matter (PM), benzene, hexavalent chromium, and others.

More information on toxics can be found at the Toxics Summaries[Internal] web page in iADAM. It contains information about trends in California. Currently there are just over 30 toxic monitoring sites located throughout California that measure toxic compounds. For information on the sources that emit toxic compounds, see the Emission Inventory Facility Search Engine[Internal].

More information regarding diesel PM is available on the Diesel Program and Activities[Internal] web page. This page provides information about the health effects of diesel PM as well as information on current regulations and programs to reduce the impacts of diesel PM.

What are indicators?

Air quality indicators are summaries of air quality measurements that reflect a particular aspect and scale of an air quality problem. Using indicators to summarize these measurements helps us to more easily understand and track air quality.

Where do you get the air quality data?

Air quality data are collected at more than 250 monitoring sites located throughout California, with more than 6,000,000 air quality measurements collected each year. These sites generally measure multiple air pollutants, as well as local weather conditions. After the data are collected, they are thoroughly reviewed to ensure accuracy and then submitted to the U.S. EPA. The data are then available in the U.S. EPA and ARB databases. These data provide the basis for the air quality indicators.

Detailed information on what is collected at each site, as well as where it is located is available through the Quality Assurance Air Monitoring Site Information Tool[Internal]. Additional sources of information can be found under the Resources tab of this FAQ.

What are air quality trends?

Trends are a useful way of looking at data over a long period for determining air quality progress. Long-term trends even out much of the year-to-year variation caused by meteorology and other factors. Thus, they give a more realistic picture of overall progress.

What indicators should I look at to determine the air quality in my area?

No single indicator provides a complete picture of air quality, because each tells a different piece of the story. Thus, we use a variety of indicators to determine compliance with the air quality standards and determine progress over time. Evaluating multiple indicators allows us to gain a better understanding of progress and the nature of the challenges an area faces. Below are a few of the most frequently used indicators.

Design Value

The design value is the concentration used to determine compliance with a national air quality standard. The design value gives an indication of the current level of air quality and how far an area has to go to attain the standard. Although the design value is calculated differently for each pollutant, it does not generally reflect the maximum measured concentration. For any particular area, a design value is calculated for each site, and the highest design value is used to determine attainment for the entire area.

Maximum Concentration

The maximum concentration is the highest measured concentration for a given time period. For example, the maximum daily 1-hour concentration reflects the highest value measured during any one of the 24 hours in a day; concentrations measured during the other 23 hours of the day may have been much lower. When using a maximum concentration indicator, it is important to remember that it merely represents the peak. More important is how often concentrations were above the level of the standard, which is a better indicator of actual exposure to harmful pollutant levels.

Exceedance Days

For many pollutants, such as ozone, concentrations are measured every day. For these pollutants, the number of exceedance days is a simple count of the number of days during a year with concentrations above the level of the standard. In contrast, other pollutants, such as PM2.5, are not necessarily measured each day. For these pollutants, the number of exceedance days is estimated, based on the number of measurements and the total number of days in the year.

This indicator gives us an idea about how often people are exposed to unhealthy air. However, it does not provide any information about how severe that exposure was with respect to pollutant levels.

Air Quality Index (AQI)

The AQI is a tool developed by the U.S. EPA for reporting daily air quality to the public. It is based on actual air quality measurements and can be used to determine when individuals sensitive to poor air quality might be affected. AIRNow[External] provides information on current and forecasted AQI levels.

Air Quality Maps

Air quality maps illustrate how the severity of an air quality problem differs across an area or from one area to another. In general, these maps are usually more highly resolved in urbanized areas, because these areas tend to have more monitoring sites. Maps are most useful for comparing relative changes over time or between areas, rather than absolute changes. Sites such as AIRNow[External] and more recent versions of ARBís Almanac[Internal] use maps to illustrate air quality.

Where can I get historical air quality measurements?

iADAM[Internal] gives you access to ADAM, Californiaís repository for official air quality data and statistics. iADAMís information includes the statistics needed for regulatory air quality evaluation (to determine whether or not an area meets ambient air quality standards, for example), as well as other commonly used air quality metrics, such as numbers of days over a standard and peak concentrations for criteria pollutants, and annual averages and risk numbers for toxics substances. iADAMís information goes as far back as 1963 in some instances, and includes all data through the most current regulatory year (usually the year before the current year).

Where can I get real-time measurements of air quality in my area?

AQMIS[Internal] can show you what is happening currently (last hour or so) based on data extracted directly from Californiaís extensive air quality and meteorology monitoring networks. These data, while preliminary and not yet official, can tell you what air quality is like today. AQMIS[Internal] also combines its preliminary data with ADAMís official data into summaries that give you an up-to-date view of this yearís air quality and allows you to compare that information to air quality data from previous years.

Where can I get information on air quality in other parts of the US?

AIRNow[External] is an excellent source of information on air quality throughout the United States. It contains helpful information on current AQI, forecasted AQI, AQI animations, as well as current ozone and PM2.5 measurements. All of these are presented on contour maps, which are described above.

Additionally, AIRNow[External] includes a number of helpful links to information about air quality and health, impacts on children and older adults, maps of monitoring locations, and other data sources, as well as resources for teachers and more.

What is my areaís air quality designation?

On ARBís designations[Internal] page, you will find links to documents containing the current designation status of all areas in California. These area designations are based on relevant air quality data and provide an indication of the healthfulness of air quality throughout the State.

I see unfamiliar terms, what do they mean?

We maintain a complete glossary[Internal] of terms on the ARB website. These terms cover nearly everything discussed on our web pages. Please feel free to contact us if we left something out or you need additional explanation.

Additional Resources

Additional resources[Internal] are available as well. The links provided include information related to topics discussed here, as well as a wide range of additional topics, from biomass burning to the top 10 industrial facilities in your area.

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