The use of data from multiple data source provides inferred air quality indices with respect to a particular pollutant for multiple areas without the addition of air quality monitor stations to those areas. Labeled air quality index data for a pollutant in a region may be obtained from one or more air quality monitor stations. Spatial features for the region may be extracted from spatially-related data for the region. The spatially-related data may include information on fixed infrastructures in the region. Likewise, temporal features for the region may be extracted from temporally-related data for the region that changes over time. A co-training based learning framework may be further applied to co-train a spatial classifier and a temporal classifier based at least on the labeled air quality index data, the spatial features for the region, and the temporal features for the region.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. One or more computer-readable media storing computer-executable instructions that are executed to cause one or more processors to perform acts comprising: obtaining labeled air quality index data for a pollutant in a region from one or more air quality monitor stations; extracting spatial features for the region from spatially-related data for the region, the spatially-related data including information associated with fixed infrastructures in the region; extracting temporal features for the region from temporally-related data for the region, the temporally-related data including data for the region that changes over time; and applying a co-training based learning framework to co-train a spatial classifier and a temporal classifier based at least on the labeled air quality index data, the spatial features for the region, and the temporal features for the region. 2. The one or more computer-readable media of claim 1, wherein the acts further comprise: obtaining spatial features for an area in the region based on spatially-related data observed for the area; obtaining temporal features for the area in the region based on temporally-related data observed for the area; generating a spatial probability score for the pollutant in the area based at least on the spatial features using the spatial classifier; generating a temporal probability score for the pollutant in the area based at least on the temporal features using the temporal classifier; and calculating an air quality index level with respect to the pollutant in the area based at least on the spatial probability score and the temporal probability score. 3. The one or more computer-readable media of claim 2, wherein the calculating includes calculating the air quality index level based at least on a product of the spatial probability score and the temporal probability score. 4. The one or more computer-readable media of claim 2, wherein the spatially-related data observed for the area includes at least one of road network data or points-of-interest data, and wherein the temporally-related data observed for the area includes at least one of automobile traffic data, human movement data, or meteorological data. 5. The one or more computer-readable media of claim 2, wherein the area lacks an air quality monitor station that provides an air quality index level for the pollutant. 6. The one or more computer-readable media of claim 1, wherein the applying includes applying the co-training based learning framework to co-train the spatial classifier and the temporal classifier for inferring an air quality index level of the pollutant for an area in the region. 7. The one or more computer-readable media of claim 1, wherein the applying the co-training based learning framework includes: training the spatial classifier with the spatial features for the region; training the temporal classifier with temporal features for the region; and applying the spatial classifier and the temporal classifier to infer unlabeled areas iteratively by adding one or more most confidently classified examples into labeled areas in the region for each subsequent training iteration round until remaining unlabeled areas in the region are labeled or a predetermined numbers of iteration rounds have been performed. 8. The one or more computer-readable media of claim 1, wherein the spatially-related data for the region includes at least one of road network data or points-of-interest data, and wherein the temporally-related data observed for the region includes at least one of automobile traffic data, human movement data, or meteorological data. 9. The one or more computer-readable media of claim 1, wherein the spatial classifier is an artificial neural network (ANN) classifier, and wherein the temporal classifier is one of a linear-chain conditional random field (CRF) classifier, a hidden Markov model (HMM) classifier, or a maximum entropy Markov model classifier. 10. A computer-implemented method, comprising: applying a co-training based learning framework to co-train a spatial classifier and a temporal classifier based at least on labeled air quality index data from one or more air quality monitor stations in a region, a set of spatial features associated with the region, and a set of temporal features associated with the region; obtaining an additional set of spatial features for an area in the region based on spatially-related data observed for the area; obtaining an additional set of temporal features for the area in the region based on temporally-related data observed for the area; generating a spatial probability score for a pollutant in the area based at least on the additional set of spatial features for the area using the spatial classifier; generating a temporal probability score the pollutant in the area based at least on the additional set of temporal features for the area using the temporal classifier; and calculating an air quality index level with respect to the pollutant in the area based at least on the spatial probability score and the temporal probability score. 11. The computer-implemented method of claim 10, further comprising: obtaining the labeled air quality index data for the pollutant in the region from one or more air quality monitor stations; extracting the spatial features associated with the region from spatially-related data for the region, the spatially-related data including information associated with fixed infrastructures in the region; and extracting the temporal features for the region from temporally-related data for the region, the temporally-related data including data for the region that changes over time. 12. The computer-implemented method of claim 11, wherein the spatially-related data for the region includes at least one of road network data or points-of-interest data, and wherein the temporally-related data observed for the region includes at least one of automobile traffic data, human movement data, or meteorological data. 13. The computer-implemented method of claim 10, wherein the applying the co-training based learning framework includes: training the spatial classifier with the set of spatial features associated with the region; training the temporal classifier with the set of temporal features associated with the region; and applying the spatial classifier and the temporal classifier to infer unlabeled areas iteratively by adding one or more most confidently classified examples into labeled areas in the region for each subsequent training iteration round until remaining unlabeled areas in the region are labeled or a predetermined numbers of iteration rounds have been performed. 14. The computer-implemented method of claim 10, wherein the spatially-related data observed for the area includes at least one of road network data or points-of-interest data, and wherein the temporally-related data observed for the area includes at least one of automobile traffic data, human movement data, or meteorological data. 15. The computer-implemented method of claim 10, further comprising: calculating a deviation between an air quality index level and a corresponding linear interpolation level for each of multiple pollutants at a plurality of areas for a set of periodic intervals; positioning a corresponding deviation for each pollutant at each of the plurality of areas and each of the periodic intervals in a multi-dimensional grid space; and applying a skyline detection algorithm to deviations in the multi-dimensional grid space to identify one or more areas for air quality monitor station installation. 16. The computer-implemented method of claim 15, wherein the applying the skyline detection algorithm includes: counting occurrences of each area in detected skylines in the multi-dimensional grid space through a predetermined time period that encompasses the set of periodic intervals; and determining that an area is a candidate location that is suitable for air quality monitor station installation based at least on a frequency that the area occurs in the detected skylines within the predetermined time period. 17. A device, comprising: one or more processors; a memory that includes a plurality of computer-executable components that are executable by the one or more processors, comprising: a spatial feature extraction component that obtains spatial features for an area in a region based on spatially-related data observed for the area; a temporal feature extraction component that obtains temporal features for the area in the region based on temporally-related data observed for the area; and an air quality index component that calculates an air quality index level with respect to the pollutant in the area by applying a spatial classifier to the spatial features or applying a temporal classifier to the temporal features. 18. The device of claim 17, wherein the spatial feature extraction component further extracts spatial features for the region from spatially-related data for the region, the spatially-related data including information on fixed infrastructures in the region, and wherein the temporal feature extraction component further extracts temporal features for the region from temporally-related data for the region, the temporally-related data including data for the region that changes over time. 19. The device of claim 17, further comprising at least one of: a labeled data extraction component that obtains labeled air quality index data for the pollutant in the region from one or more air quality monitor stations; a spatial probability component that generates a spatial probability score for a pollutant in the area based at least on the spatial features for the area using the spatial classifier; a temporal probability component that generates a temporal probability score for the pollutant in the area based at least on the temporal features for the area using the temporal classifier; and a co-training component that applies a co-training based learning framework to co-train the spatial classifier and the temporal classifier based at least on the labeled air quality index data, the spatial features for the region, and the temporal features for the region, wherein the air quality index component further calculates an additional air quality index level with respect to the pollutant in the area based at least on the spatial probability score or the temporal probability score. 20. The device of claim 17, further comprising a location identification component that performs acts including: calculating a deviation between an air quality index level and a corresponding linear interpolation level for each of multiple pollutants at a plurality of areas for a set of periodic intervals; positioning a corresponding deviation for each pollutant at each of the plurality of areas and each of the periodic intervals in a multi-dimensional grid space; and applying a skyline detection algorithm to deviations in the multi-dimensional grid space to identify one or more areas for air quality monitor station installation.