Lidar remote sensing of aerosol and ozone profiles and application to air quality studies in New York City area
Ozone (O3) and PM2.5 (Particulate Matter with a diameter less than 2.5 μm) are the main pollutants in New York City (NYC) due to high levels of anthropogenic emissions, complex urban meteorology, and regional transport. However, vertical distribution observations are still lacking. This thesis utilizes lidar remote sensing techniques to retrieve the vertical distribution of O3 and aerosols and study air pollution episodes in the NYC metropolitan area. The thesis includes three parts. The first part analyzes continuous ceilometer observations of aerosols and atmospheric mixed-layer height (ML). We investigate the vertical, diurnal, and seasonal characteristics of the correlation between ceilometer attenuated backscatter coefficients and ground PM2.5, and aerosol homogeneity. Results show better overall correlation between attenuated backscatter and ground PM2.5 in summer, with less degradation in correlation with height during summer. Seasonal variation in the regression slope is observed, partially explained by different aerosol size distributions and speciation between summer and winter. Aerosols are well-mixed within the lower part of the ML up to 500 m. The second part introduces a forward iterative method to derives aerosol backscatter coefficient from ceilometer observations. Results show good consistency between aerosol backscatter coefficient profiles from the Lufft ceilometer and co-located elastic-Raman lidar retrieval. Error simulations indicate that the relative uncertainty of aerosol backscatter coefficient in the ML is 10-20% due to a calibration error of 10%, and less than 4% due to a lidar-ratio error of 10%. The third part demonstrates an integrated Ozone Differential Absorption Lidar (DIAL)/Aerosol Lidar development at CCNY. The DIAL uses an Nd:YAG laser pumping a CO2 Raman cell for transmitter, and two telescopes for receiver, covering ozone measurement from near-surface to upper troposphere. The ozone retrieval from the DIAL shows statistical uncertainties below 8% for 1.5-hour profile below 8 km. Validations with other measurements indicate the reliability of the CCNY-Ozone DIAL. Observations of DIAL and other in-situ measurements in summer 2022 reveal a strong diurnal pattern of ozone concentration within the PBL and regional transport by sea breeze. In summary, simultaneous observations of aerosol and O3 vertical distribution complement the surface observations by NYS Department of Environmental Conservation and contribute to exploring air pollution formation mechanisms, improving air quality forecasts, and evaluating satellite remote sensing applications.
Lidar, Ceilometer, DIAL, PM2.5, Ozone, Aerosol, Electrical and Electronics, Other Electrical and Computer Engineering
City University of New York - City College
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