4. Synergy-based approach for incorporation of the lidar near-surface maps into modern air-quality monitoring systems

movements of deficient in aerosols air masses from the mountain areas to the city, driven by

Figure 13. Colormap of the aerosol density distribution as measured on 5 November 2015 in the time intervals 18:37–

On 6 November 2015, three (two daytime and one nighttime) mapping lidar measurements were carried out within an angular sector of 26° over the same area. The two daytime measurements

Figure 14. Colormap of the aerosol density distribution as measured on 6 November 2015 in the time intervals 10:24–

11:39 LT (a), 11:48–11:53 LT (b) and 18:23–19:19 LT (c), at distances of up to 4 km (a, b) and 10 km (c).

the evening mountain breeze—characteristic of the Sofia region.

19:33 LT (a), 19:36–20:29 LT (b) and 20:35–21:28 LT (c), at distances of up to 12 km.

102 Aerosols - Science and Case Studies

As shown in the previous sections, the aerosol lidar mapping technique is capable of providing a fast, accurate, and reliable range-time-resolved determination of optical parameters of the near-surface aerosols, such as the extinction and backscattering coefficients (directly proportional to the aerosol mass concentration), covering broad observation areas. In order to achieve complete quantitative aerosol characterization, determination of the aerosol mass concentration itself is also required. On the other hand, the existing set of in-situ air-pollution detectors present at some sites in the city is able to determine the aerosol mass concentration. However, this is possible to be done just for a limited number of detector location points. We consider that, by combining the two mentioned approaches, particularly by using in-situ obtained data to calibrate the aerosol lidar measurements, a synergistic effect could be achieved, allowing direct mapping of the aerosol mass concentration over the whole urban area. Below, we analyze and discuss the possibilities of achieving such a synergy in the characterization of near-surface aerosol pollutions.

As is well known, the typical existing air monitoring city systems contain the following basic structural components: (1) a network of a limited number of in-situ aerosol, gas, and biological sensors; (2) a network of meteorological sensors; (3) a modeling and data-processing system. The use of a low number of sensors by two networks over large urban areas imposes serious limitations on the information capabilities of the air-quality systems. The lidar maps can be considered as being a (virtual) aerosol sensor network of closely distributed very large number of single aerosol sensor cells of dimensions determined by the lidar maps' spatial resolution. Therefore, the lidar mapping of near-surface aerosol fields appears to be a promising technology for improving the information quality of air-monitoring systems. The combination of the three sensor networks mentioned above incorporated in a joint air-quality monitoring system would provide a synergistic aerosol characterization.

Finally, we have to note that aerosol lidar maps could provide large amounts of additional information about the near-surface atmosphere. They contain data on the near-surface dynamics of air masses, driven by the surface winds but affected by the city structures. This is an important view of a better evaluation of the pollution transport over an urban area. Also, applying multiwavelength lidar mapping, one could contribute to the characterization of the aerosols' size parameters, as well as to identifying their types and origin.
