Air quality problems persist in the Northern Front-Range Metropolitan Area (NFRMA) of Colorado despite efforts to reduce emissions, and summertime ozone concentrations in the NFRMA frequently exceed the NAAQS. Atmospheric modeling in the NFRMA is challenging due to the complex topography of the area, as well as diversity of pollutant sources (urban NOx and VOCs, power plants, industrial complexes, oil and gas, agricultural emissions, biogenic emissions, and wildfires). An improved understanding of the local atmospheric chemistry will enable researchers to advance these atmospheric models, which will subsequently be used to develop and test more effective air quality management strategies. The Front Range Air Pollution and Photochemistry Experiment (FRAPPE) investigates this problem through detailed examination of atmospheric chemistry in the NFRMA, including photochemistry, aerosol and oxidant formation and fate, and meteorological flow patterns. Our project specifically explores the spatial variability in ozone (O₃) concentration and dry deposition within the FRAPPE study area.

One source of uncertainty in atmospheric models is ozone flux, which varies spatially due to local meteorology and variation in ambient concentration and deposition velocity. Model grid cells typically range in size from 10-100 km and 100-500 km, for regional and global models, respectively. With the reduction of sub-grid variability in mind, the monitoring sites used for model inputs are chosen to be representative of the surrounding areas, but accurate representations of an entire grid cell cannot always be achieved. Large spatial variability within a model grid cell can lead to poor estimates of trace-gas flux and concentration. Our research addresses this issue by measuring spatial variability in O₃ flux using low-cost dry-deposition flux chambers.

We are measuring O₃ and CO₂ flux with 5 low-cost flux chambers and one eddy-covariance tower. The eddy-covariance tower is located at the Boulder Atmospheric Observatory in Erie, CO. All 5 chambers are within a 8.3 x 6 km square, with one chamber collocated with the eddy-covariance tower, and the other 4 chambers at distances of 0.33, 1.14, 3.22, and 7.55 km from the tower. The largest distance between any two chambers is 8.5 km. All 5 chambers measure flux onto native grasslands across a range of natural variability in species, leaf-area index, and ecosystem productivity. Preliminary results show that ambient ozone concentrations and fluxes vary between sites.  A detailed analysis of the variability in O₃ fluxes and concentrations across measurement sites will be presented.