Chemical Filter Conditions
Chemical filter conditions determine the subset of the chemical data for which the
backtrajectories are extracted, rendered, or gridded. The chemical filters fall into three major
categories, filtering by parameter (e.g. SO4), location or by time. Setting filter conditions for
these three data dimensions as well as conditions on the value of the chemical parameter, offers
a rich toolkit for exploring the chemical transport conditions.
The filter settings are accessible through the Query form, loaded by the query button, Q, on the
right side of the map view of the Data Viewer. In the query form figure below, the parameter,
location and time settings are highlighted for better orientation.
In the section below, the settings of the parameter, location and time filters are explained.
Specific filter combinations are presented for browsing the combined aerosol- trajectory
database, ranging from a simple back-trajectory at a specific location and time to ensemble
trajectories arising from elaborate filtering/aggregation operations. However, this open, flexible,
web-based analysis tool was designed to encourage user-experimentation with various userdefined filers and aggregators.
Parameter Filter
The CATT chemical filter always operates on a specific single chemical parameter such as fine
particle sulfate with param_abbr=SO4f. The filtering by parameter may also include conditions
that depend on the value of the selected parameter. The parameter selection can be either by
filling in the param_abbr field or by selecting the parameter from the list at the top of the
DataViewer.
The parameter settings can be entered through the main chemical query form. Under the section
param_filter_conditions, the main choices for param_filter are:
1. Expression: only data points that satisfy the expression, e.g. value>5, are extracted.
2. Percentile: data points within the percentile range for a specific site are extracted, e.g. 95100%.
3. All values: all non-null data points are extracted regardless of their value.
Clearly the purpose of the param_filter_condition is to identify parameter values particularly the
high and low outliers.
Location Filter
The purpose of the location filter is to determine for which locations the trajectories should be
extracted. Under loc_filter_conditions, the choices for loc_filter are:
1. Loc_code: Trajectories extracted for one selected site
2. Loc_code_list: Trajectories extracted for a user-specified list of sites, entered in the query
form
3. Loc_range: Trajectories extracted for sites within in a latitude-longitude range set by the
zoom rectangle of the Viewer
4. All locations: Trajectories extracted for all locations
The utility of the location filter is to define for which site or geographical region the trajectories
should be extracted. Single locations can be selected by (1) clicking on the site in the Map View,
(2) filling in the query form, (3) use the Location selection list at the top of the Data Viewer.
Time Filter
The time_filter_conditions specify the time range and/or month-of-year for which the trajectories
are to be extracted. The time_filter has three choices:
1. Datetime: Data points extracted for a single day.
2. Datatime_list: Data points extracted for a list of user-supplied dates.
3. Datetime_range: Data points within the time range set by the TimeView of the data
viewer.
4. All Datetimes: All data points regardless of the sampling date.
An additional time filter allows the filtering by specific month of the year. This filter is always
applied in addition to the selected time filter. For instance, if the datetime_range is set to be
2000-2004 and the month filter is set to July only, then all the July data points for 2000-2004
will be selected.
Application of Filter for Data “Slicing”
The above filtering allows selection of data points from a ‘data cube’ with dimensions parameter,
location and time. Depending on the settings, the three-dimensional data cube can be “sliced” to
highlight different aspects of the data. For instance selecting data for a single date yields a spatial
data slice (backtrajectories) for all locations for that day. This
Conversely, selecting a specific location returns a temporal data slice, i.e. backtrajectories for all
dates for that site.
Below is a, illustrated list of specific filter conditions that yield useful data views through CATT.
Of course, the user is encouraged to explore other settings, thus enriching the CATT family of
tools. These examples are derived from the default CATT_T page:
http://webapps.datafed.net/dvoy_services/datafed.aspx?page=CATT_T
Single Site, Single Day Trajectories
Settings:
param_filter = all values
loc_filter = loc_code
time_filter = datetime
There is a cursor on both the map view (a blue cross) and on the time view (a black vertical line).
The cursor location can be moved by (1) clicking on the site in the Map View, (2) filling in the
query form, (3) use the Location selection list at the top of the Data Viewer. The time-cursor for
the back trajectory can be set (1) clicking on the site in the Time View, (2) filling in the query
form, (3) use the Time selection box at the top of the Data Viewer. Note that when the map view
shows no data that means that the day is not a sampling day. Click on the arrow buttons < > at
the top of the viewer to move one day before or after the current date.
This simple CATT mode is most useful when the backtrajectory for a specific chemical data
point is to be viewed.
Multi-Site, Single Day Trajectories
For exploring the backtrajectories at multiple user-specified sites for a give day, the filter settings
are:
param_filter = all values
loc_filter = loc_code_list (user specified)
time_filter = datetime
In this mode, the list of receptor locations is fixed as specified by the loc_code_list (e.g. e.g.
ACAD1 SHEN1 GRSM1 UPBU1). This list can only be changed in the query form; moving the
location cursor in the map view will not change the loc_code_list . The time navigation for this
setting is the same as above.
This CATT mode is helpful to show the airmass histories for specific sites that have unique
features identified by the user.
All Sites, Single Day Trajectories
The overall transport pattern can be explored by the this mode, where all the backtrajectories are
shown for all the sites that have data on that day.
Settings:
param_filter = all values
loc_filter = loc_range (defined by the map view zoom rectangle)
time_filter = datetime
In this mode, the list of receptor locations include all the sites that are in the zoom rectangle of
the map view. Moving the location cursor in the map view will not change the selected
trajectories. The time navigation for this mode is the same as above: clicking on time view,
changing the Time cursor at the top of the viewer and by changing the value of the datetime field
(2001-05-04) in the query form. The setting loc_filter = all_locations differs from loc_range
only selecting all stations, including the once outside the map view zoom rectangle.
This single-day trajectory browsing mode provides a rich description of the transport conditions
a given day. The trajectory rendering is enhanced color-coding and by changing the line
thickness of the trajectories in proportion to the magnitude of the parameter value. . The
trajectory rendering is set by the RT button (trajectory render-settings are described elsewhere).
In this example, rainbow coloring is used. Trajectories with receptor SO4 concentration of 0 are
shown as thin blue line. Trajectories with SO4 concentration over 20 ug/m3 are shown as heavier
red lines. This color/thickness coding of trajectories conveys in an intuitive way the transport
direction where ‘dirty’ and ‘clean’ air is coming from.
Limiting Trajectories by Parameter Value
Limiting the trajectories to a give value range can highlight the origin of either high or low
concentrations of a species on a given day.
Settings:
param_filter = expression
expression = value > 5
loc_filter = loc_range (defined by the map view zoom rectangle)
time_filter = datetime
In the above example, the SO4 parameter was restricted to expression = value > 0 and value > 20
respectively. Imposing a value filter can eliminate ‘irrelevant’ trajectories, while highlighting
those with ‘interesting value range.
Single Site, Time-Range Trajectories
The ensemble of backtrajectories to a single site illustrates the transport climatology to a specific
site.
Settings:
param_filter = all values
loc_filter = loc_code (a single user-selected location)
time_filter = datetime_range (time range set in the time view of the DATA VIEWER)
Preferential airmass transport pathways are clearly evident in this view. For example airmasses
to Big Bend NP, TX (BIBE1) arrive predominantly from the Gulf of Mexico (SE), from the
Pacific (W) and through the Great Planes from Canada. Evidently, air from the Northeast never
transported directly to Big Bend.
Enhancing high receptor concentration trajectories with reddish colors and thicker lines enhances
the value of the ensample trajectories. For example at Big Bend, the high SOILf concentration
(red) is originating either from the SE or from the West.
The seasonal values
July, SOILf
April, SOILf > 5
July, SOILf > 5
April, SOILf > 5
Percentile Filter
Settings:
param_filter = percentiles (set at 0-20 or 80-100)
loc_filter = loc_code (a single user-selected location)
time_filter = datetime_range (time range set in the time view of the DATA VIEWER)
shows transport for hilo conditions
Sommer Hi-Lo percentile
Winter Hi-Lo percentile
Gridding and Grid Operators
Filtered Grid
Reference Grid
Grid Operator
Grid Rendering