HEI Air Quality Database

The Map Browser

On the browser page, a background map is shown with state boundaries and contours of concentrations. The background map shows the concentration field that is interpolated from the 2005 annual average concentrations (in µg/m³ at 54 core and approximately 200 supplemental sites. The background map can be changed. The choices are contour maps of elemental carbon (EC), organic carbon (OC), nitrate, fine particulate matter (FPM), ammonium, and sulfate. The background map is changed by clicking on one of 6 buttons underneath the map.

Overlaid on the map are the locations of 54 STN core sites. When the mouse is moved to point at a site, the site location lights up and a call-out box displays its name, station ID, latitude, longitude, and local population. For sites that appear close together, the neighboring sites are displayed on the right hand side of the call-out box. A neighboring site can be selected by moving the cursor over the name of the neighboring site and clicking when the name is highlighted. The selected neighbor will be highlighted as a result and a call-out box will then be displayed for that neighbor.

The user can also select a display of all core STN and supplemental sites by selecting "all sites". The mouse over feature functions the same way for displaying additional information regarding each site. Rural sites that are not located in a city are identified by their station numbers. A longer list of neighboring sites is listed for each site because of the proximity of many sites. The display of all sites on the map and the corresponding mouse-over feature may be slow due to computational resources available on the client computer. To switch back to the core site display, click on "core sites".

Clicking on the site or on the name of the site in the call out box calls up two summary graphics for that site. The summary graphics include time series for PM and its major components (sulfate, nitrate, ammonium, EC, OC) and a pie chart indicating the average PM composition for 2005. In calculating the composition, OC is converted to OM using a factor of 1.4 to account for hydrogen, oxygen, and nitrogen that are not measured.

From the time series and pie chart graphics, one can click on "Return to site map" to go back to the map browser.

Time Series and Pie Chart Visualization

Time series of PM_2.5 (FPM), sulfate, nitrate, ammonium, EC, OC are displayed for each site (labeled by its State Code, County Code, and Site identification numbers). All available information is used in these plots. When multiple co-located measurements are available, the average concentrations are plotted. To save the graphics, right click anywhere on the plots and use the "save picture as" option to save a gif format file onto the local computer. From the time series and pie chart graphics, click on "Return to site map" to go back to the map browser.

View Station Characteristics

If you find a site worthy of further investigation from the map browser, you can type in its station identification number, which is a concatenation of the state code (2 digits), county code (3 digits) and site identification (ID) number (4 digits) in the "Look up Site Characteristics by Station Number" page, which is accessible from the home page. Multiple stations can be probed by typing in their station numbers separated by commas.

View Station Characteristics — Results

The station characteristics that are provided include: State, County, SiteID, latitude, longitude, city, population, point source emissions (tons/year), area source emissions, on-road mobile source emissions, non-road mobile source emissions, land use, setting, monitoring objectives, and co-located data or nearest neighbors for CO, ozone, SO2, NOx, temperature, pressure, relative humidity, wind speed, and wind direction if co-located data do not exist.

Selecting and Saving a List of STN Sites

There are 3 different ways to make a list of STN sites

1. Using the "Query by Site Characteristics" page
2. Using the "Query by Data Characteristics" page
3. Choosing from a list of all sites

From each page, a query can be saved to be used in raw data extraction.

STN Query by Site Characteristics

Site characteristics that can be used as criteria for site selection include (1) location, (2) population, (3) nearby emissions, (4) land use, (5) setting, and (6) monitoring objectives. If several criteria are placed under multiple characteristics, they have to be simultaneously satisfied for a site to be selected in the query.

Location information. Each site is identified by several attributes related to its location

• State and County (the Site ID number in the Air Quality System (AQS) database contains a 2-digit State Code, a 3-digit County Code and a 4-digit SiteID)
• Latitude and longitude
• City (if site is within an urban area)

On the top part of the "STN Query by Site Characteristics" page, there are three tabs for the selection "by State/County/Site", "by Latitude/Longitude" or "Cities". Only one type of information can be queried at one time, to avoid incompatible combinations of state/county/site and latitude/longitude and cities. Clicking on a tab will change the form to be filled in by the user.

State/County/Site tab. The State/County/Site tab contains three drop down menus for States, Counties and Sites. The default for each of these fields is "any" and the default query will result in the output of all 54 core STN sites. The selection process starts with State. Once a State is selected, the choices in the County and Site drop down menus are limited to those consistent with the State selection.

Latitude/Longitude tab. The Latitude/Longitude tab allows the user to specify a range of latitude/longitude locations inside which sites are selected. There are two rows under that tab, one for each coordinate. For each coordinate, the user can formulate the following numeric criteria:

• Latitude/longitude = value
• Latitude/longitude < (<=) value
• Latitude/longitude > (>=) value

The logical symbols (<, <=, =, >=, >) are selected from a drop down menu. After the logical symbol is selected, a value needs to be entered into the box following it. To define a range between value1 and value2, the user can use either statement below:

• Latitude/longitude < (<=) value2 > (>=) value1
• Latitude/longitude > (>=) value1 < (<=) value2

When two criteria are specified, they are applied in combination; i.e., both criteria have to be satisfied before a site is selected.

Cities tab. The Cities tab provides a drop down menu of all cities with available STN monitors. Multiple cities can be selected by holding the shift key while clicking with the mouse.

In addition to location, which can be selected in one of three ways as discussed above, other criteria can be used to select sites.

Population. Population is a numeric field. Two comparative criteria can be placed on population. The user can formulate the following criteria using only one criterion line by selecting a logical symbol (<, <=, =, >=, >) and typing a value:

• Population = value
• Population < (<=) value
• Population > (>=) value

The user provides a range of population (between value1 and value2) by using two criteria to be satisfied simultaneously.

• Population < (<=) value2 > (>=) value1
• Population > (>=) value1 < (<=) value2

The default for population selection is to place no criterion on the field by leaving the value boxes empty.

Population data are for cities as identified in the census data of 2000. Population for the metropolitan statistics area (obtained from EPA's meta data associated with the AQS database) is included in the database; this field can be displayed in the results of the site selection process.

Nearby emissions of particulate matter (PM_2.5). The form can be used to construct queries based on emission characteristics of fine particulate matter within that county where the STN site is located. There are 4 types of emissions on which one or two criteria can be placed. The definition of a criterion is similar to that described above for population. The four types of emissions, as defined by EPA, are:

• Point (or stationary) sources. Point sources are identifiable by name and location. For example, electric power plants and refineries are considered point sources. A "major" source emits a threshold amount (or more) of at least one criteria pollutant, and must be inventoried and reported. Many states also inventory and report stationary sources that emit amounts below the thresholds for each pollutant.
• Mobile sources. Mobile sources are sources that do not have fixed location, including any kind of vehicle or equipment with a gasoline or diesel engine; airplane; or ship. Mobile sources are further categorized to be:
  • On-road: licensed motor vehicles, including automobiles, trucks, buses, and motorcycles.
  • Non-road: vehicles or equipment not suitable for highway use, e.g., farm or construction equipment, planes, trains, ships and boats.
• Area sources. Area sources are small point sources such as a home or office building, or a diffuse stationary source, such as wildfires or agricultural tilling. These sources do not individually produce sufficient emissions to qualify as point sources. Dry cleaners are one example, i.e., a single dry cleaner within an inventory area typically will not qualify as a point source, but collectively the emissions from all of the dry cleaning facilities in the inventory area may be significant and must, therefore, be included in the inventory.

Emissions (in tons per year) are numeric fields. Each of these four categories can be used independently as a selection criterion. In order to formulate a criterion, the user needs to select a logical symbol (<, <=, =, >=, >) and type a value. For example:

• Point = value
• Point < (<=) value
• Point > (>=) value

A range of values can be selected by using two logical symbols and typing in two values:

• Point < (<=) value2 > (>=) value1
• Point > (>=) value1 < (<=) value2

The default for emissions selection is to place no criterion on the any of the emission fields by leaving the value boxes empty for point, mobile, non-road and area sources.

STN Query by Site Characteristics — Results

The number of STN sites that fit the criteria defined in the STN query by site characteristics form will be displayed above the detailed results.

Above the table of results, there are options for "new query", "modify query" and "save this query". The "new query" button returns the user to a blank "Query by Site Characteristics" page. If you wish to view your selections on the "Query by Site Characteristics" page that corresponds to the results page, use the “back” button of your browser to return to the filled out Query by Site Characteristics” form where your selection criteria are retained. (You may have to use the refresh button on the browser if the query page has been timed out.)

The "modify query" option allows you to return to the query page with your selection criteria for the current query are retained.

The "save query" option allows you to save the list of sites for use in the data download stage, if you are satisfied with the characteristics of the sites that have been selected based on the site characteristics query. You need to log in to save the information on the host computer and access the saved information at a later time. If you are already logged in, you will be connected to a “Save Query” page. If you have not already logged in, when you click on the “save query” option, you will be asked to type in your user name and password, in order. A successful log in will bring up the “Save Query” page.

The default display of results will be the "quick view" format, which contains only 6 columns: State, County, Site ID, latitude, longitude, and city. (Information regarding State and County codes can be found under “meta data” accessible from the homepage.) The results table can be sorted (numerically or alphabetically in ascending order) using any of these 6 fields by clicking on the underlined column header. For example, if one clicks on the word “City” on the screen shown in Figure 3a, the list will be sorted as shown in Figure 3b.

Save Query

In order to save the results of the previous query, you will need to type in a name and a brief description on the Save Query page. For example, information regarding the criteria used in the selection process can be stored in the description area. Then click on the "submit" button. If the save query action is successful, a confirmation message will be displayed (xxxx query saved, where xxxx is the name of the query you provided) and a new query will appear on the right hand side under "saved queries".

Because the data in the database tables will be updated periodically, a saved query (based on site characteristics or data characteristics) will generate the most up-to-date result based on the current version of the database.

From the "save query" page, you can click on the link to "manage existing queries".

STN Query by Data Characteristics

This form allows the user to select sites based on the availability, completeness and characteristics of measurements taken at the site. For example, one can select sites that have co-located gaseous or meteorology data, or sites where data are at least 75% complete, or sites with mean sulfate concentrations greater than 3 μg/m3.

In the top part of this page, the user can check different species to identify sites with co-located measurements of those species.

• gas-phase measurements of ozone, CO, SO2, NOx
• meteorological measurements of temperature, relative humidity, pressure, wind speed, wind direction (under construction)

Gaseous and meteorology measurements are taken as part of the national air monitoring stations (NAMS) or state and local air monitoring stations (SLAMS). Because the configuration of the monitoring network can change from time to time, the co-location of measurements may also vary from one year to the next. In this database, the existence of co-located sites is based on 2005 data.

Another source of meteorology data is the National Climatic Data Center (Integrated Surface Hourly Observations). These data are typically not co-located with STN data and so they are not used in the site selection process for co-located sites.

The second part of the page allows the selection of sites with specific monitoring schedules. STN measurements are 24-hour averages starting midnight local time, and only 24-hour average data are included in this database. Many of the STN sites operate every third day. But there are instances where a more (everyday or every other day) or less frequent (e.g., every 6th day) schedule is used. In the AQS database, each measurement is accompanied by a collection frequency code. Most instruments (unique Parameter Occurrence Code (POC) for a given site) are operated at a fixed schedule throughout the year, and the frequency is defined by the collection frequency. However, some instruments are operated using different frequencies at different times of the year. For these instruments, a dominant frequency is defined to be the collection frequency associated with the largest number of samples. A few instruments are operated with a "random" frequency. These data points do not factor into the calculation of the dominant frequency. Invalid entries for data frequency (such as 0) are not included in the determination of dominant frequency. Under the frequency menu, one can select all available sites or sites where the measurements are taken on a one in six (6), one in three (3) or everyday (1) schedule.

The user can select sites associated with a minimum number of data points or that fulfill a data completeness criterion during a given year. To prevent the use of incompatible criteria for number of data points and data completeness, only one of these two fields can be selected at a time. The number of available valid observations is counted for each parameter, site, and year and is stored in a summary table for users to query. These measurements are associated valid collection frequencies. To use number of data points as a selection criterion, the user simply types in a positive value in the "sample" box.

By definition, data completeness is a value between 0% and 100%. Data points associated with a "random" sampling schedule do not factor into the calculation of data completeness. For any given year, data completeness is calculated using the following formula:

Data_completeness = (Number_of_Samples) / (365 / Dominant_Frequency)

where Dominant_Frequency = 1, 2, 3, or 6. There are some errors in the AQS database in the collection frequency entry. If the entered frequency is lower than the actual frequency, data completeness will appear to be greater than 100%. If the entered frequency is higher than actual, the data stream will appear incomplete. There is no good way to distinguish between the sites that have incomplete data and the sites that are associated with erroneous collection frequency entry. Therefore, no attempt was made to correct the raw AQS data for suspected errors in collection frequency entries.

The last part of the Query by Data Characteristics page allows the user to select sites with particular PM or species concentration characteristics. To select based on concentrations, the user first check one or more species onto which to apply a criterion:

• PM_2.5
• Sulfate
• Nitrate
• Ammonium
• OC
• EC

For each checked species, the user can then select the metric (mean or median) where the numeric criterion is placed. The user then defines the criterion by selecting a logical symbol and typing a numeric value. Using one comparison, the criterion may be in one of the follow formats:

• Concentration > (>=) value
• Concentration = value
• Concentration < (<=) value

A range can be defined using two comparisons to be applied simultaneously:

• Concentration > (>=) value1 < (<=) value2
• Concentration < (<=) value2 > (>=) value1

Once the requirements on co-located measurements, data count or completeness, and concentration characteristics of various species are specified, the user can execute the query by clicking on "submit". Otherwise, the "clear" button allows the user to restart the selection process from default entries.

STN Query by Data Characteristics — Results

By default, the results page will provide the number of sites that fulfilled the criteria specified in the data characteristics query. There is a link to "view data values" after the number of sites. Below, a table lists the site characteristics, including State, County, Site ID, latitude, longitude, and city. Similar to the "Site Characteristic Query - Results" page, the user can select a quick view or comma delimited presentation of the data. A map of the selected sites will be generated on demand. The neighbors tab is available for viewing co-located measurements where available and closest neighbors where co-located measurements are not available. The user can also choose to save the query and its results.

Clicking on the view data values link will open a new page that lists the available mean and count values of PM_2.5, sulfate (SO4), nitrate (NO3), ammonium (NH4), organic carbon (OC) and elemental carbon (EC) at all stations and instruments (POC) that fulfill the criteria in a given year.

Create a Station List/Build Site List

If the user already knows the list of sites (identified by State codes, County codes, and Site ID) of interest, he/she can make the list by selecting individual sites on this page. Meta information on State and County codes is available from the "meta data" page, which can be accessed from the home page. Give the list of sites a name, then click on a site on the left panel followed by ">>" to include it in the selected list. One can also click on multiple sites by holding down the shift key. When finished, check the list of sites on the right hand side. A site can be removed from that list by clicking on it and then the "<<" button. When finished, click on "submit" to finish Step 1. For Step 2, the user is asked to provide some description of the list. The list will then be saved, and can be used in a query for raw data or accessed from the "Manage Saved Query" page.

Query Raw Air Quality (PM and Gas) and Meteorology Data

Site Codes. The extraction of raw data is based on a pre-selected list of sites, either by querying site characteristics, data summary characteristics or manually choosing a list of sites. See discussion above for selecting and saving a list of STN sites. The saved site queries are available for selection on the drop down menu under "select a saved station list". If a list of sites is not already defined, or a new list is desired, there is a link ("click here") directly to the "STN Query by Site Characteristics" where a new list can be defined.

Specify Parameters. Check the parameters corresponding to the raw data you wish to download. The available PM parameters are PM_2.5 mass and PM_2.5 components, sulfate, nitrate, ammonium, organic carbon, organic carbon, elemental carbon. Beginning with the November 2006 release, data for organic carbon blanks are available for download. PM and blanks data are available as 24-hour averages, which is the standard operating procedure for STN at present. Also available from the database are trace element data. By clinking on the text "more trace PM2.5 species" under the boxes for PM2.5 mass, sulfate, nitrate, ammonium, organic carbon, and elemental carbon, a box will appear with the available PM_2.5 trace elements. The user can select multiple elements by holding the control key while clicking on the choices. All available data will be downloaded; each element is downloaded in one data file.

The available gaseous pollution data are CO, ozone, SO2 and NOx. The available meteorology data are temperature, pressure, relative humidity (AQS) or dew point (NCDC), wind speed, and wind direction. Raw gaseous and meteorological data are available as one-hour average data. These data are processed into various 24-hour metrics to be used in conjunction with PM data. For the gases, the available metrics are: (1) daily average (24-hour), (2) daily maximum 8-hour average, and (3) daily maximum one-hour average. A data completeness criterion of 75% is applied in these calculations. Therefore, the daily average value is calculated if there are at least 18 hours' worth of valid data during the 24-hour period from midnight to midnight local time. If insufficient data exist to calculate the daily average, a value of -99.000 is used to denote invalid data entries. The same data completeness criterion is also applied to the maximum one-hour and 8-hour averages. If there are insufficient valid data to cover 75% of the 24-hour period, the maximum one-hour and 8-hour average concentrations are not calculated for that day. For meteorology, only 24-hour average and maximum one-hour average are available in the database. A 75% data completeness criterion is also applied in the calculation of the 24-hour average and 1-hour maximum. The treatment of wind direction is different from the other meteorological parameters. For 24-hour data, a dominant wind direction is identified as one of 8 compass directions, N, NE, E, SE, S, SW, W, NW. For 1-hour data, the wind direction associated with the maximum one-hour wind speed is given.

As a default, co-located gaseous or meteorological measurements only from the AQS data base will be included in the output. The user has a couple of options regarding the meteorology data (1) to allow substitution of the closest neighbor if co-located data do not exist for both gases and PM and (2) to use NCDC data, which are not typically co-located with STN data, instead of AQS data for meteorological measurements. Either of these two options is allowed by clicking on the corresponding boxes.

The user will be able to select a subset of the data by providing a start date and an end date.

At present, comma delimited files are generated as a default.

The user clicks Submit to start a background query job. The following notice is provided: "Your job has been submitted. This may take a few minutes. To check on the status and download completed query results, go to the Manage Queries page." Follow that link to check the status of the submitted query and to download the data files generated by the query.

"Clear" unchecks all the choices and allows the user to start over again.

Figure 6 shows an example of data request for PM2.5 mass, key components, and OC blanks, together with co-located or nearby ozone data. Figure 7 shows the same example, except that chromium (Cr) and copper (Cu) concentrations in PM2.5 are also to be downloaded if available at the sites on the list called CAsites.

Manage Existing Queries and Download Extracted Data

This page can be assessed from the "Save Query" page or from the Home page. There are two parts to this page. The first part lists all the saved queries. The second part lists the status of any background query jobs that have been submitted.

Manage Saved Queries. Saved queries are listed by name. These queries are used to generate a list of sites where certain site or data characteristics are fulfilled. By clicking on the query name, the query results are displayed. You can also access different views and generate a map of those selected sites.

Also displayed under saved queries are the type of query (site characteristics queries, data characteristic queries or sites selected from the site list) and the date on which it is saved. Each user is allowed to save a maximum of 25 queries. You can delete unwanted queries by checking the box next to the query and selecting delete. Queries more than 6 months old will be removed from the system automatically.

If you click on a specific query, information about that query is displayed on a new page for that query, including the query name, number of sites extracted, date of last modification, comments. Below this information, the actual site list is provided, together with information that is displayed as a result of site queries.

Queries can be edited, e.g., adding and deleting sites, by using the "edit site list" button.

Edit Site List

The edit site list page is a utility that allows the user to change the site list without going through the query process. This page is accessed from the "manage save queries page" after one clicks on a specific query to be modified. A site is deleted from the existing list by clicking on it inside the box on the right hand side and then clicking on the "<<" button. The list of available sites and selected sites will both be updated so that the deleted site now appears on the left hand side and disappears on the right hand side. Similarly, a site is added by highlighting it on the "available list" then clicking on the ">>" sign. The new selected list will show the new addition, while it is removed from the available list. Multiple sites can be added or removed this way by holding down the shift or control key while highlighting. You can revert to original to start over. To finish, click on "save site list". You will be asked to provide a list name and comments. You can also replace the original list or save as a new list. The new list will be saved as a list of sites, with no associated query procedures to generate the list. Any information (in the SQL statement) related to the criteria used to generate the original list will be lost if the modified list overwrites the original query.

Manage Background Queries. The second part of the page shows the status of background query jobs that have been submitted. Background jobs include queries on the raw data table for PM mass and speciated PM and associated meteorology and gaseous pollutant data and some advanced queries. The information provided include query process ID (qpid), name of query, status, start and finish time, and a link to the file(s) that are generated by the query.

Queries and results can be deleted by checking the box next to the query name and then selecting "delete" at the bottom of the page. The "clear" button unchecks all the checked boxes.

To download the results, click on "link to files" on the right hand column. A separate page will be brought up to display the status of that particular query, including qpid, query name, status, start and finish times, file names and the number of rows retrieved for each file. Some queries generate more than one file because data for each parameter is placed in separate files. The filenames are formulated as xxx_ppppptt_yyyymmddhhmmss.csv, where xxx is an internal user ID, ppppp is the parameter code (e.g., PM25 for PM_2.5 mass, so4 for sulfate, p is for pressure, vis for visibility; trace elements are identified by their chemical symbols except for phosphorus, which is identified as "Ph" instead of "P"), tt denotes any temporal aggregation (e.g., 24h for 24-hour average temperature data, 1h is the daily one-hour maximum), and the last digits are the year, month, day, hour, minute, and second when the result file was generated. The result file is in comma delimited format, hence the extension *.csv. Older files may be compressed for disk space management.

You can then click on the file names to download the results, which are in comma delimited format. The header provides information on the query and the number of rows retrieved. The body of the file contains columns as follows: StationID (State, County, SiteID for AQS data or a 6-digit AWS code for NCDC data), corresponding STN Station ID (State, County, Site ID) for gas and meteorology data only, Parameter, the type of blank (field vs. trip) if Parameter is OC blanks, POC, date, start time (in local time), concentration (in microgram per cubic meter for PM, ppb for gases, degrees Celsius for temperature and dew point, hectopascal for pressure, meter per second for wind speed and angular degree for wind direction).

Advanced Site and Data Query

Users who are familiar with the SQL language can formulate other query and output. The user can query from one table at a time. Using the advanced query page, the user can select data from the tables containing monitor characteristics table (STN_Summary), PM summary data (STN_Summary_statistics), summary of OC blank data (STN_Summary_statistics blanks), PM concentrations (SPEC), carbon blank concentrations (SPEC_blank), time-averaged gaseous concentrations and meteorology from AQS, or time-averaged meteorology from NCDC.

The fields available are provided once a table is chosen. The user first click on the field to be displayed, then type in his criteria in the box under "where" using the fields in the table selected. The raw data are stored using AQS codes, which would be needed if an advanced user wishes to place a criterion on the extraction. Refer to the "meta data" page for code options for State, County, and Parameters.

To submit the query, click on "validate". If your query is valid, the database will return the number of rows to be retrieved. You then have a choice to obtain the results on the screen or as a csv file, suitable for large amounts of data. The csv file can be downloaded from the "manage query page".