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Air Quality Index Report

What does the report tell me?

The AirData Air Quality Index Summary Report displays an annual summary of Air Quality Index (AQI) values for counties or core based statistical areas (CBSA). Air Quality Index is an indicator of overall air quality, because it takes into account all of the criteria air pollutants measured within a geographic area. Although AQI includes all available pollutant measurements, you should be aware that many areas have monitoring stations for some, but not all, of the pollutants. Each row of the AQI Report lists summary values for one year for one county or CBSA. The summary values include both qualitative measures (days of the year having "good" air quality, for example) and descriptive statistics (median AQI value, for example).

Summary statistics for the current year are incomplete because data are still being reported and quality assured. Data for the current year are considered preliminary until May 1 of the following year. Therefore, comparing reported values for the current year with previous years may not be valid.

How can I sort the report?

You can sort the report by clicking on any column heading. The first time you click on a column, it will sort in ascending order. If you click again, it will sort in descending order.

What do the report columns mean?

# Days with AQI
Number of days in the year having an Air Quality Index value. This is the number of days on which measurements from any monitoring site in the county or MSA were reported to the AQS database.

# Days Good
Number of days in the year having an AQI value 0 through 50.

# Days Moderate
Number of days in the year having and AQI value 51 through 100.

# Days USG - Unhealthy for Sensitive Groups
Number of days in the year having an AQI value 101 through 150.

# Days Unhealthy
Number of days in the year having an AQI value 151 through 200.

# Days Very Unhealthy
Number of days in the year having an AQI value 201 or higher. This includes the AQI categories very unhealthy and hazardous. Very few locations (about 0.3% of counties) have any days in the very unhealthy or hazardous categories.

AQI Max
The highest daily AQI value in the year.

AQI 90th %ile
90 percent of daily AQI values during the year were less than or equal to the 90th percentile value.

AQI Median
Half of daily AQI values during the year were less than or equal to the median value, and half equaled or exceeded it.

# Days CO
# Days NO2
# Days O3
# Days SO2
# Days PM2.5
# Days PM10
A daily index value is calculated for each air pollutant measured. The highest of those index values is the AQI value, and the pollutant responsible for the highest index value is the "Main Pollutant." These columns give the number of days each pollutant measured was the main pollutant. A blank column indicates a pollutant not measured in the county or CBSA.

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Air Quality Statistics Report

What does the report tell me?

The Air Quality Statistics Report displays air pollution values related to national standards for air quality. This report includes pertinent values for all six criteria pollutants. The report lets you see if an area's maximum air quality statistics are above the level of the national standards for a particular year. Each row lists standards-related air pollution statistics for all six criteria pollutants, for a single area, for one year. The values shown are the highest reported during the year by all monitoring sites in the county or CBSA. A statistic that exceeds the level of an air quality standard is highlighted in red.

Summary statistics for the current year are incomplete because data are still being reported and quality assured. Data for the current year are considered preliminary until May 1 of the following year. Therefore, comparing reported values for the current year with previous years may not be valid.

How can I sort the report?

You can sort the report by clicking on any column heading. The first time you click on a column, it will sort in ascending order. If you click again, it will sort in descending order.

What do the report columns mean?

CO 1-hr 2nd Max
For Carbon Monoxide, the 2nd highest 1-hour measurement in the year.

CO 8-hr 2nd Max
For Carbon Monoxide, the 2nd highest non-overlapping 8-hour average in the year.

NO2 98th %ile
For Nitrogen Dioxide, the 98th percentile of the daily max 1-hour measurements in the year.

O3 1-hr 2nd Max
For Ozone, the 2nd highest daily max 1-hour measurement in the year.

O3 8-hr 4th Max
For Ozone, the 4th highest daily max 8-hour average in the year.

SO2 99th %ile
For Sulfur Dioxide, the 99th percentile of the daily max 1-hour measurements in the year.

SO2 24-hr 2nd Max
For Sulfur Dioxide, the 2nd highest 24-hour average measurement in the year.

PM2.5 98th %ile
For PM2.5, the 98th percentile of the daily average measurements in the year.

PM2.5 Wtd Mean
For PM2.5, the Weighted Annual Mean (mean weighted by calendar quarter) for the year.

PM10 24-hr 2nd Max
For PM10, the 2nd highest 24-hour average measurement in the year.

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Monitor Values Report

What does the report tell me?

The Monitor Values Report displays air pollution measurements recorded by thousands of monitoring sites throughout the United States. The report shows a yearly summary of the measurements at individual monitors and descriptive information about the sites. Each row of the Monitor Values Report displays air pollution levels measured at a single monitor in a single year. The same site may appear in multiple rows if it has more than one monitor for the same pollutant.

Summary statistics for the current year are incomplete because data are still being reported and quality assured. Data for the current year are considered preliminary until May 1 of the following year. Therefore, comparing reported values for the current year with previous years may not be valid.

How can I sort the report?

You can sort the report by clicking on any column heading. The first time you click on a column, it will sort in ascending order. If you click again, it will sort in descending order.

What do the report columns mean?

Duration Description
This is the averaging time for the selected pollutant. Note that some pollutants are reported at multiple averaging times. Ozone, for example, is reported as a 1-hour statistic and as an 8-hour statistic. Both are relevant to existing and previous ozone standards.

Obs
Number of observations reported for the year. Some pollutants are measured hourly and some are measured daily. Uninterrupted hourly monitoring would produce 8760 obs per year (24 hours * 365 days).

Exc Events
States can flag data that may have been influenced by an exceptional event (e.g. high winds, wildfire). This column indicates whether there were any flagged data ('NONE'), whether flagged data were included ('INCLUDED') or excluded ('EXCLUDED'). You can select whether you want to include or exclude exceptional events data when you create the report.

Monitor Number
An ID number that distinguishes among monitors for the same pollutant at a particular monitoring site. In the AQS database, this identifier is called parameter occurrence code (POC).

Site ID
The AQS database identification code for an air monitoring site. An AQS site ID has the following parts:

  • FIPS state code (2 digits)
  • FIPS county code (3 digits) - FIPS is the acronym for Federal Information Processing Standards, which defines codes used in most U.S. government information systems.
  • AQS site code (4 characters) - an arbitrary code that identifies a particular monitoring site within a county
For example, AQS site ID 10-003-2004 is a monitoring site in Wilmington, DE (10 = Delaware, 003 = New Castle County, 2004 = a monitoring site in Wilmington). In AirData reports, this site ID is displayed as 100032004, with no hyphens separating the parts of the ID.

Address
Address where the monitoring site is located.

City
Name of the city, town, village or other municipality in which the site is located. Blank if the site is not located within such a jurisdiction, or if no value was provided.

County
Name of the county (or equivalent jurisdiction) in which a site is located.

State
Postal abbreviation for the state or territory in which a site is located.

EPA Region
EPA Region number in which the site is located. There are ten EPA regions.

Pollutant Statisics
The report columns displayed depend on which pollutant you select. The following describe the columns for each pollutant.

CO - Carbon Monoxide
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest 1-hour values in the year, in parts per million by volume (ppm).
Actual Exceedances
Number of 1-hour values exceeding the level of the 1-hour standard during the year.
8-Hour values
Computed by AQS software for each hour of the day as a moving average of eight 1-hour values.
Obs
Number of 1-hour values (observations) reported for the year.
1st Max, 2nd Max
Highest and second-highest non-overlapping 8-hour values in the year, in parts per million by volume (ppm). Non-overlapping means that the 8-hour averages do not include any of the same 1-hour values.
Actual Exceedances
Number of non-overlapping 8-hour values exceeding the level of the 8-hour standard during the year. If the number is greater than one, it is highlighted.
NO2 - Nitrogen Dioxide
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest daily max 1-hour values in the year, in parts per billion by volume (ppb).
98th Percentile
98th percentile of the daily max 1-hour values in the year, in parts per billion by volume (ppb).
Actual Exceedances
Number of daily max 1-hour values exceeding the level of the standard during the year.
O3 - Ozone
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest "daily max values" in parts per million by volume (ppm). Take the highest 1-hour value of each day, and pick the top four of those values.
Actual Exceedances
Number of days in the year when the daily max 1-hour value exceeded the level of the 1-hour standard.
Estimated Exceedances
Calculated number of days in the year when 1-hour values would be estimated to exceed the level of the 1-hour standard, after compensating for days when scheduled monitoring did not occur.
Required Days
Number of days in the year when ozone monitoring is required. This is normally the length of the "ozone season" -- months when ozone is a potential problem -- at the monitoring site. In many locations ozone monitoring is required April - October (214 days).
Valid Days
Number of days in the year when the requisite number of 1-hour values were reported: at least 9 values between 9:00 a.m. and 9:00 p.m. (local time).
Percent Days
Percentage of required monitoring days having valid 1-hour data: 100*(# Valid Days)/(Required Days).
Missing Days
Number of days in the year presumed not to have exceeded the level of the 1-hour standard even though the requisite number of 1-hour values were not available.
8-Hour values
Computed by AQS software for each hour of the day as a moving average of eight 1-hour values.
Obs
Number of 8-hour values (observations) reported for the year.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest "daily max values" in parts per million by volume (ppm). Take the highest 8-hour value of each day, and pick the top four of those values.
Actual Exceedances
Number of days in the year when the daily max 8-hour value exceeded the level of the 8-hour standard.
Estimated Exceedances
Calculated number of days in the year when 8-hour values would be estimated to exceed the level of the 8-hour standard, after compensating for days when scheduled monitoring did not occur.
Required Days
Number of days in the year when ozone monitoring is required. This is normally the length of the "ozone season" -- months when ozone is a potential problem -- at the monitoring site. In many locations ozone monitoring is required April - October (214 days).
Valid Days
Number of days in the year having valid 8-hour average values for at least 18 hours of the day. A least six 1-hour values must be available during an 8-hour period to calculate a valid 8-hour average.
Percent Days
Percentage of required monitoring days having valid 8-hour data: 100*(Valid Days)/(Required Days).
SO2 - Sulfur Dioxide
1-Hour values
Hourly average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of 1-hour values (observations) reported for the year. Uninterrupted monitoring would produce 8760 values per year (24 hours * 365 days).
1st Max, 2nd Max
Highest and second-highest daily max 1-hour values in the year, in parts per billion by volume (ppb).
99th Percentile
99th percentile of the daily max 1-hour values in the year, in parts per billion by volume (ppb).
Actual Exceedances
Number of daily max 1-hour values that exceeded the level of the 1-hour standard during the year.
24-Hour values
Computed by AQS software for each day as an average of 1-hour values.
Obs
Number of 1-hour values (observations) reported for the year.
1st Max, 2nd Max
Highest and second-highest 24-hour average SO2 concentrations in the year, in parts per million by volume (ppm).
99th Percentile
99th percentile of the 24-hour values in the year, in parts per billion by volume (ppb).
Actual Exceedances
Number of 24-hour average SO2 concentration values that exceeded the level of the 24-hour standard during the year.
PM2.5 - Particulate Matter smaller than 2.5 micrometers
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of days in the year for which values (observations) were reported. Many sites take measurements every day.
1st Max, 2nd Max, 3rd Max, 4th Max
The four highest 24-hour values of the year, in micrograms per cubic meter.
98th Percentile
The 98th percentile 24-hour value, in micrograms per cubic meter. This value is higher than 98 percent of 24-hour values for the year.
Annual values
Computed by AQS software from 24-hour values.
Weighted Annual Mean
Arithmetic mean of 24-hour values, in micrograms per cubic meter. (Concentrations are rounded to the nearest 0.1 microgram for comparison with the 24-hour standard.)
PM10 - Particulate Matter smaller than 10 micrometers
24-Hour values
Daily average concentrations measured by monitoring equipment and reported to AQS.
Obs
Number of 24-hour values (observations) reported for the year. PM10 is typically measured every sixth day, which results in about 60 values per year. Some sites take measurements every day.
1st Max, 2nd Max
The two highest 24-hour values of the year, in micrograms per cubic meter.
Actual Exceedances
Number of days in the year when a 24-hour value exceeded the level of the 24-hour standard. .
Estimated Exceedances
Calculated number of days in the year when 24-hour values would be estimated to exceed the level of the 24-hour standard if monitoring took place every day.

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Monitor Values Report - Hazardous Air Pollutants

What does the report tell me?

The Monitor Values Report for Hazardous Air Pollutants (HAPs) displays air pollution measurements collected by thousands of monitoring sites throughout the United States for 42 Core HAPs (minus unverified acrolein) plus others from the list of the 33 urban air toxics. This link provides the complete list of HAPs included in the AirData Monitor Values Report. The report shows a yearly summary of the measurements at individual monitors and descriptive information about the sites. Each row of the report displays air pollution levels measured at a single monitor in a single year. The same site may appear in multiple rows if it has more than one monitor for the same pollutant.

Summary statistics for the current year are incomplete because data are still being reported and quality assured. Data for the current year are considered preliminary until May 1 of the following year. Therefore, comparing reported values for the current year with previous years may not be valid.

How can I sort the report?

You can sort the report by clicking on any column heading. The first time you click on a column, it will sort in ascending order. If you click again, it will sort in descending order.

What do the report columns mean?

Obs
Number of observations reported for the year. Some pollutants are measured hourly and some are measured daily or less frequently such as every third day or every sixth day. A pollutant measured every six days would produce about 60 samples per year. Uninterrupted hourly monitoring would produce 8760 obs per year (24 hours * 365 days).

Obs < MDL
Number of observations below the Method Detection Limit (MDL). The MDL is the lowest concentration that can be detected by a sampling instrument and method. By default, there is a Federal MDL associated with each instrument and method. If available, an Alternate MDL, which is a value provided by the reporting agency for the specific concentration, is used. It is considered more precise and specific to the sample than the Federal MDL.

Obs Nondetect
Number of values (observations) that are reported as zero, or nondetect.

Max Fed MDL
Maximum Federal MDL related to the parameter in the queried year.

Max Alt MDL
Maximum Alternate MDL related to the parameter in the queried year.

Data Complete
Indicates whether the annual summary data meet a minimum 75 percent completeness based on the monitor's operating schedule and monitoring frequency. For example, if a monitor is scheduled to take a 24-hour sample every 6 days for a year, then there needs to be 46 valid samples. Data for a monitor scheduled to operate 3 months of the year may be deemed complete as long as the number of valid samples is sufficient during the 3 months.

Min
The lowest sample value in the year.

10th %ile
The 10th percentile of all the sample values in the year.

Median
The median of all the sample values in the year.

Mean
The mean of all the sample values in the year.

90th %ile
The 90th percentile of all the sample values in the year.

95th %ile
The 95th percentile of all the sample values in the year.

Max
The highest sample value in the year.

Units
The units for the displayed summary statistics. In most reports of AQS data, the units of measure for most gaseous HAPs are PPBC. For this report the units of measure for gaseous HAPs were converted from PPBC to ug/m3 as follows: ug/m3=PPBC * MW * (1/#Carbons) * (1/24.436).

Parameter Name
The name of the parameter (pollutant).

Monitor Number
An ID number that distinguishes among monitors for the same pollutant at a particular monitoring site. In the AQS database, this identifier is called parameter occurrence code (POC).

Site ID
The AQS database identification code for an air monitoring site. An AQS site ID has the following parts:

  • FIPS state code (2 digits)
  • FIPS county code (3 digits) - FIPS is the acronym for Federal Information Processing Standards, which defines codes used in most U.S. government information systems.
  • AQS site code (4 characters) - an arbitrary code that identifies a particular monitoring site within a county

For example, AQS site ID 10-003-2004 is a monitoring site in Wilmington, DE (10 = Delaware, 003 = New Castle County, 2004 = a monitoring site in Wilmington). In AirData reports, this site ID is displayed as 100032004, with no hyphens separating the parts of the ID.

Address
Address where the monitoring site is located.

City
Name of the city, town, village or other municipality in which the site is located. Blank if the site is not located within such a jurisdiction, or if no value was provided.

County
Name of the county (or equivalent jurisdiction) in which a site is located.

State
Postal abbreviation for the state or territory in which a site is located.

EPA Region
EPA Region number in which the site is located. There are ten EPA regions.

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Air Quality Index Daily Values Report

What does the report tell me?

The Air Quality Index Daily Values Report provides daily AQI values for the specified year and location. If you select an individual pollutant, then each row contains the date, the AQI value for the selected pollutant, and the corresponding AQI category. If you select to see "All AQI Pollutants", then each row contains the date, the AQI values for all pollutants measured, the "overall AQI value" (which is the maximum of the individual pollutant AQI values on that date), and the "main pollutant" (which is the pollutant having the maximum value on that date). The table is color-coded to reflect the AQI categories.

How can I sort the report?

You can sort the report by clicking on any column heading. The first time you click on a column, it will sort in ascending order. If you click again, it will sort in descending order.

What do the report columns mean?

Date
The calendar date with which the AQI value(s) are associated.

Overall AQI Value
The maximum of the individual pollutant AQI values on a given date. The background color corresponds to the AQI category (Good, Moderate, etc.) This column is displayed only when you select "All AQI Pollutants" from the options list.

Main Pollutant
The pollutant having the maximum AQI value on a given date. This column is displayed only when you select "All AQI Pollutants" from the options list.

AQI Value (for Ozone, PM2.5, SO2, NO2, PM10, or CO)
The AQI value for each pollutant. The background color corresponds to the AQI category (Good, Moderate, etc.)

AQI Category
The AQI category (Good, Moderate, etc.). This column is displayed only when you select an individual pollutant from the options list.

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