Using Observations and Source‐Specific Model Tracers to Characterize Pollutant Transport During FRAPPÉ and DISCOVER‐AQ

Abstract

Transport is a key parameter in air quality research and plays a dominant role in the Colorado Northern Front Range Metropolitan Area (NFRMA), where terrain‐induced flows and recirculation patterns can lead to vigorous mixing of different emission sources. To assess different transport processes and their connection to air quality in the NFRMA during the FRAPPÉ and DISCOVER‐AQ campaigns in summer 2014, we use the Weather Research and Forecasting Model with inert tracers. Overall, the model represents well the measured winds, and the inert tracers are in good agreement with observations of comparable trace gas concentrations. The model tracers support the analysis of surface wind and ozone measurements and allow for the analysis of transport patterns and interactions of emissions. A main focus of this study is on characterizing pollution transport from the NFRMA to the mountains by mountain‐valley flows and the potential for recirculating pollution back into the NFRMA. One such event on 12 August 2014 was well captured by the aircraft and is studied in more detail. The model represents the flow conditions and demonstrates that during upslope events, frequently, there is a separation of air masses that are heavily influenced by oil and gas emissions to the north and dominated by urban emissions to the south. This case study provides evidence that NFRMA pollution not only can impact the nearby foothills and mountain areas to the east of the Continental Divide but that pollution can “spillover” into the valleys to the west of the Continental Divide.

Chemical Characteristics and Ozone Production in the Northern Colorado Front Range

“…Complex meteorology and flow patterns due to the high elevation and varied terrain and a mix of diverse pollution sources (e.g., urban emissions, strong point sources such as large power plants and industrial complexes and airports, and area sources such as agricultural emissions, emissions from oil and gas development, biogenic emissions, and wildfires) in the NFR pose challenges with respect to characterizing, modeling, and forecasting air quality and the underlying processes. In summer 2014, the State of Colorado and NSF Front Range Air Pollution and Photochemical Experiment (FRAPPÉ) and the fourth deployment of the NASA DISCOVER‐AQ were carried out jointly to investigate the drivers of summertime ozone in the NFR (Pfister et al, ). A comprehensive set of chemical and meteorological measurements was collected from five aircraft, multiple mobile vans, ozonesondes, lidars, tethered balloons, and also at numerous operational and additional surface sites between 15 July and 20 August 2014 with most DISCOVER‐AQ platforms ending on 10 August.…”

Measurement of formic acid, acetic acid and hydroxyacetaldehyde, hydrogen peroxide, and methyl peroxide in air by chemical ionization mass spectrometry: airborne method development

“…Elevated HFo (> 1.5 ppb) in Granby corresponded to elevated O 3 (∼ 80 ppb, NCAR one-channel chemiluminescence; Ridley et al, 1992) and a biogenic signature (∼ 100 ppt MVK and ∼ 80 ppt isoprene). This could be secondary production from an upslope flow event and subsequent spillover event (Pfister et al, 2017). There was high AAES (up to 14 ppb) below 0.5 km (a.g.l., above ground level) corresponding to high NH 3 (Aerodyne Research, Inc., Herndon et al, 2005) with a maximum mixing ratio of 180 ppb near Greeley, which is an area associated with a concentration of confined animal feedlot operations (Eilerman et al, 2016;Yuan et al, 2017).…”

Assessing a low-cost methane sensor quantification system for use in complex rural and urban environments

“…Data from two field deployments are used to discuss the different considerations for calibrating and deploying these sensors. The first dataset was collected in Colorado during the FRAPPE/DISCOVER-AQ monitoring campaigns in the summer of 2014 (Pfister et al, 2017). This deployment primarily measured rural and semirural areas along the Front Range north of Denver; important sources of methane in the area include oil and gas development and agriculture/ranching.…”