Since over 70% of carbon emissions are from urban areas, it is of great importance to develop an effective measurement technique that can accurately monitor atmospheric CO₂ in global urban areas. Remote sensing could be an effective way to achieve this goal. However, due to high aerosol loading in urban areas, there are large, inadequately resolved areas in the CO₂ products acquired by passive remote sensing. China is planning to launch the Atmospheric Environment Monitoring Satellite (AEMS) equipped with a CO₂-light detecting and ranging (LIDAR) system. This work conducted a feasibility study on obtaining city-scale column CO₂ volume mixing ratios (XCO₂) using the LIDAR measurements. A performance framework consisting of a sensor model, sampling model, and environmental model was proposed to fulfill our demand. We found that both the coverage and the accuracy of the LIDAR-derived city-scale XCO₂ values were highly dependent on the orbit height. With an orbit height of 450 km, random errors of less than 0.3% are expected for all four metropolitan areas tested in this work. However, random errors of less than 0.3% were obtained in only two metropolitan areas with an orbit height of 705 km. Our simulations also showed that off-nadir sampling would improve the performance of a CO₂-Integrated Path Differential Absorption (IPDA) LIDAR system operating in a 705 km orbit. These results indicate that an active remote sensing mission could help to effectively measure XCO₂ values in urban areas. More detailed studies are needed to reveal the potential of such equipment for improving the verification of carbon emissions and the estimation of urban carbon fluxes.

Activities involving firecrackers and fireworks on Chinese New Year's Eve (NYE) are common in Chinese culture. Previous studies revealed that such human activities significantly influence the ambient air quality and negatively impact human health. However, both the academia and the public lack a deep understanding of the extent and consequences of such human-induced air pollution. Therefore, it is important to evaluate the effects of these Spring Festival celebrations on ambient air quality at a large spatial scale and a fine temporal resolution. Data from ten monitoring stations distributed around Wuhan and a Lidar system provide a good opportunity to gain insight into spatial and temporal distribution of contaminants due to the NYE celebrations. Dramatic increases in PM_2.5 and PM₁₀ mass concentrations due to NYE celebrations were observed in this study. Moreover, the ratio of residential to total area was found to be a significant factor in predicting the geographic distributions of contaminants. The vertical distribution of such human-induced and culture-related contaminants was first shown using a Mie Lidar. Contaminants emitted by firecrackers on the ground spread to a distance of over 450 m in the atmosphere. The vertical influence began to fade two hours after celebrations because of dry deposition. Moreover, it took over 15 hours for the contaminant levels to return to pre-celebration levels. Finally, estimations of PM_2.5 emissions from firecrackers in Wuhan were 39.57 and 43.51 tons, based on regression and time series analyses, respectively.

A differential absorption lidar (CO2-VDIAL), which is designed for vertical CO2 profile retrieving by using aerosol-scattered signals, is demonstrated in this paper. To our knowledge, it is the first time that a dye laser has been utilized to realize the wavelength modulation for a CO2-DIAL/IPDA system. Such a design scheme greatly reduces both the threshold and the cost to develop a CO2-DIAL. However, two key problems emerge in this system, i.e., wavelength stability and broad bandwidth. By adopting the CO2-VDIAL, a dual-path gas cell, and the Voigt fitting procedure, the accurate wavelength calibration of infrared pulse laser is achieved. Experimental results show that the error of wavelength calibration can be suppressed under 0.1 pm. And a wavelength stability of ～2 pm is then achieved. For tackling the error introduced by using the laser of a broad bandwidth, simulated experiments are carried out to estimate its influence. On that basis, we propose a method to calculate the correction coefficient and demonstrate the process via experiments by using a gas cell. It is demonstrated that the bandwidth of the output infrared laser is around 600-700 MHz. Hence, the broad bandwidth correction is an indispensable step for this CO2-VDIAL. Finally, horizontal, vertical and continuous detections are carried out to verify the precision and the accuracy of our CO2-VDIAL. The slope method is used to retrieve the XCO2 in the above experiments. In the horizontal detections, an R2 of 0.999 is achieved, suggesting that the precision of the system is excellent. By comparison with the in-situ measurements, a difference is found to be lower than 4 ppm. Consequently, it is concluded that the CO2-VDIAL is capable of providing retrievals with the high precision and accuracy. Moreover, the XCO2 decreases with increasing altitude according to the vertical detection experiment in the midnight on June 19m th 2015 at an urban site, demonstrating that the CO2-VDIAL is capable of providing retrievals of ranged-resolved. Finally, temporal characteristic of XCO2 can be also revealed by the CO2-VDIAL in light of continuous detections. The CO2-VDIAL has already been assembled in a container which is due to be transported to Huainai for further verifications in late 2015. Once we finish the performance optimization, the CO2-VDIAL will be installed in Tibet for long period observation.