Synthesis of FRAPPÉ

The Front Range Air Pollution and Photochemical Experiment (FRAPPÉ) was designed to identify and quantify the main drivers of summertime ozone in the Colorado Front Range and took place jointly with the NASA DISCOVER -AQ in summer 2014. The analysis of the field campaign data has to date resulted in about 40 peer-reviewed publications. The wealth of findings and conclusions from these studies as well as a summary of the NCAR FRAPPÉ Report prepared for the State of Colorado have been summarized in an Overview Paper and submitted to J. Geophys. Res. This Overview Paper also describes the measurement resources and sampling strategy, and discusses the general conditions of the regions in terms of meteorology and emissions and the conditions leading to efficient ozone production.  

High ozone days in the Colorado Front Range are typically characterized by high pressure, summertime meteorological situations that favor stable conditions and little external forcing. These conditions favor clear skies and the development of light upslope or cyclonic local winds which cause mixing of local ozone precursor emissions, efficient ozone production and transport into the western suburbs and adjacent mountains. Numerous studies have identified emissions from oil and natural gas (O&NG) activities as one of the major contributors to surface ozone, albeit the quantification of their role varies with the methodology applied and the considered region and time period. This emission sector is also identified as carrying the largest uncertainties in currently available emission inventories, both with regard to magnitude and emission factors. On average , emissions from the transportation sector are estimated as being about equally important as O&NG emissions for ozone production in the region. The benefit of multi-scale and multi-faceted experimental and modeling studies to derive robust conclusions on source contributions has been demonstrated. 

A multitude of studies has also focused on the transport of pollution from the NFRMA into the pristine mountain areas to the west of NFRMA and demonstrated the large impact the NFRMA human footprint exerts on the air quality in these remote regions. 

The comprehensive suite of measurements provided the basis for careful evaluation of different processes in 3D chemical transport models and accurate model representation of meteorology and transport has shown crucial for the model’s chemical performance. Consideration needs to be given to the representativeness of observations to ensure that model output is evaluated correctly. The studies point towards the need for improvements in simulating meteorology including the representation of clouds and winds, specifically wind speed at high altitude terrain. There is also a need to revisit current mechanism chemistry, including possible missing peroxy radicals at high NO or NOx levels or the treatment of organic nitrate chemistry.

A large number of science questions have been addressed and advanced with the to date published studies but some data sets and topics remain insufficiently exploited and should be utilized in future studies. Amongst these are the pollution inflow into and outflow out of the Front Range region, the assessment of emissions from individual processes using VOC canister samples collected nearby selected emission sources, characterization and evaluation of powerplant emission from analysis of dedicated aircraft passes, the contribution of agricultural emissions, the spatial and temporal variability in NOx and VOC sensitivities across the region or the application of inverse modeling techniques to better constrain emission inventories for different sectors.

Figure 1. Impressions from FRAPPÉ and DISCOVER-AQ 2014.