Reactive nitrogen in Rocky Mountain National Park during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE)
Nitrogen emissions from locations outside of Rocky Mountain National Park have the potential to negatively impact the ecosystems within the park. Measurements made during Front Range Air Pollution and Photochemistry Experiment (FRAPPE) were designed to improve our understanding of sources and transport of nitrogen to the region. Sample collection took place in July and August 2014. At our monitoring site in Rocky Mountain National Park, co-located with the IMPROVE and CASTNet ROMO site, measurements were made of CO, NO, NO2, NOx, NOy, NH3, and total reactive nitrogen (TNx) at 1 minute time resolution using Teledyne continuous gas monitors and a Piccaro cavity ringdown system with a heated inlet for ammonia. Additional measurements of NH3 and HNO3 and PM2.5 ions were made at hourly resolution using a MARGA and also at 24-hour time resolution using URG denuder-filter pack sampling. Precipitation samples were collected to quantify wet deposition of ammonium, nitrate, and organic nitrogen. Additional measurements of organic gases were made using online gas chromatography at hourly time-resolution and a proton transfer reaction-mass spectrometer (PTR-MS) at 6-minute time resolution.
Ammonia concentrations increased in the early morning almost every day suggesting bi-directional exchange of ammonia may be an important process in the region. We also observed larger increases in concentration associated with changing wind direction suggesting transport of ammonia from sources to the east is also important. Higher concentrations of NOx and NOy were observed in the daytime compared to the evening but in general the diurnal trend differs from ammonia. Several upslope events were observed during the measurement period during which NOx, 2-propylnitrate, 2-butylnitrate, ethane, butane, and pentane were observed to increase in concentration along with ozone. Higher concentrations of ammonia were also observed during days with upslope winds. We also look at the influence of biomass burning events on atmospheric nitrogen species measured at the ground site including those already mentioned and acetonitrile.