DIAL and Doppler Lidar Characterization of the Boundary Layer for Air Quality and Greenhouse Gas Emissions Studies
Oil and gas extraction can impact local air pollution and greenhouse gas concentrations. Volatile organic carbon (VOCs) emissions can combine with locally produced nitrogen oxides to elevate ozone levels above levels where human health can be impacted. Also, leakages of methane at the wellhead, if sufficiently high, may reduce or even eliminate the inherent advantage of burning natural gas instead of coal to reduce greenhouse gas emissions. Transport and downward mixing of ozone generated from anthropogenic activity or forest fires upwind may also impact local air quality, pushing ozone and aerosol concentrations above EPA standards. To study the impact of oil and gas emissions and local meteorology on ozone concentrations, ESRL lidars were deployed in the Uintah basin near Vernal Utah, and near the Denver-Julesburg oil and gas field in north-central Colorado. The Vernal studies focused on high wintertime ozone concentrations, which were shown to be caused by a combination of high emissions of ozone precursors, enhanced albedo due to snow cover, and a very thin surface-based layer into which the precursors were emitted. The Denver study, which took place during the summer of 2014 in conjunction with the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) project deployment, showed how ozone concentration varied as a function of atmospheric meteorological and radiative properties. In both cases, the combination of ozone and Doppler instruments enabled investigation of the effects of stability and transport on ozone and aerosol structure.
Improving methods for estimating greenhouse gas emissions from large areas such as urban metropolitan regions or oil and gas fields is important for assessing current emissions levels as well as monitoring future progress in reducing emissions. We have applied Doppler lidar techniques to characterize boundary layer structure in support of observation and model-based efforts to improve measurement methodologies. The lidar provides profiles of wind speed and direction, turbulence, and backscatter structure, which are analyzed in conjunction with aircraft and surface based measurements of gas concentrations. Results from studies near oil and gas fields in Utah, Colorado, and Texas have validated the use of this technique to measure leakage rates from oil and gas wells. Additionally, we have deployed a commercial Doppler lidar as part of the Indianapolis Flux Experiment (INFLUX) aimed at developing and validating new methodologies for estimating urban scale emissions. The lidar operated continuously for more than one year in this application, producing estimates of key parameters for use in mass balance greenhouse gas emissions studies. Results from the INFLUX study, which included several comparisons with the ESRL High Resolution Doppler research lidar and aircraft studies, showed the value of Doppler lidar observations for such studies.