Remote Sensing Instruments Used for Measurement and Model Validation of Optical Parameters of Atmospheric Aerosols

With the dramatical climate changing that we are facing today, atmospheric monitoring is of major importance. Several atmospheric monitoring instruments are already being deployed for real-time surface-level retrieval of atmospheric composition, optical coefficients, particulate matter less than 2.5 μm in diameter (PM 2.5 ), aerosol optical depth (AOD), and particle size distribution. However, these measurements are, in general, very cost intensive and can realistically be deployed only over very limited areas. Therefore, it is very important that advanced modeling methods be employed to fill these gaps and provide air quality predictions that can be used for forecasts as well as a better understanding of the interplay of meteorology, atmospheric emissions, and chemistry. In particular, for the New York State area, the New York State Department of Environmental Conservation uses Community Multiscale Air Quality (CMAQ) model to couple meteorology to local emissions, and there is intense interest in trying to assess the model performance beyond current surface network measurements. In particular, a deeper understanding of boundary layer processes can be made by experimentally exploring the vertical distribution model forecasts to better understand the underlying causes when model forecast results are not accurate. To this end, we develop a comprehensive Mie-scattering-based procedure including the effects of relative humidity that allows us to convert CMAQ aerosol distribution data into vertical-profile multiwavelength optical parameters that can be compared to column-integrated and vertical-profiling measurements to assess model performance and point to areas where the model is deficient. In particular, we make use of multiwavelength light detection and ranging (LIDAR), sunphotometer, ceilometer, and existing tapered element oscillating microbalance (TEOM) measurements to assess various vertical and column-integrated parameters of the CMAQ model under different stability conditions. In particular, we find that, for cases where the planetary boundary layer (PBL) is stable, the column-integrated AOD comparisons are in good agreement unlike the days with dynamic PBL. This is also consistent with observations that the TEOM PM 2.5 trends are closely followed by the CMAQ model during these stable conditions. On the other hand, significant errors between the surface CMAQ PM 2.5 and TEOM measurements can occur which can be traced to unphysically high particulate concentration profiles distributed too close to the surface not seen in ceilometer/LIDAR profiles. Finally, we note that, even for the stable cases, the multiwavelength optical depth data show that, for sufficiently low wavelengths, the column AOD in the model is underestimated, illustrating that there is a general underestimation of ultrafine (Aitken) particulates which can dramatically affect health.