Abstract
Abstract. The environmental impacts of atmospheric particles are highlighted in remote areas where visibility and ecosystem health can be degraded by even relatively low particle concentrations. Submicron particle size, composition, and source apportionment were explored at Rocky Mountain National Park using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer. This summer campaign found low average, but variable, particulate mass (PM) concentrations (max = 93.1 μg m−3, avg. = 5.13 ± 2.72 μg m−3) of which 75.2 ± 11.1% is organic. Low-volatility oxidized organic aerosol (LV-OOA, 39.3% of PM1 on average) identified using Positive Matrix Factorization appears to be mixed with ammonium sulfate (3.9% and 16.6% of mass, respectively), while semi-volatile OOA (27.6%) is correlated with ammonium nitrate (nitrate: 4.3%); concentrations of these mixtures are enhanced with upslope (SE) surface winds from the densely populated Front Range area, indicating the importance of transport. A local biomass burning organic aerosol (BBOA, 8.4%) source is suggested by mass spectral cellulose combustion markers (m/z 60 and 73) limited to brief, high-concentration, polydisperse events (suggesting fresh combustion), a diurnal maximum at 22:00 local standard time when campfires were set at adjacent summer camps, and association with surface winds consistent with local campfire locations. The particle characteristics determined here represent typical summertime conditions at the Rocky Mountain site based on comparison to ~10 years of meteorological, particle composition, and fire data.
Highlights
From alpine meadows to stark peaks, Rocky Mountain National Park (RMNP) hosts abundant wildlife, an important water catchment, and roughly 3 million visitors per year (Annual Park Visitation Report, NPS Public Use Statistics Office)
The ambient submicron aerosol at the RMNP ROMO site during 2 July–31 August 2010 is low in average concentration, dominated by highly oxidized organics (LV-OOA and semi-volatile oxidized organic aerosol (SV-OOA)), and punctuated by short biomass burning (BBOA) episodes
A biogenic contribution, possibly from oxidation of BVOCs as Front Range oxidant-rich pollution plumes are transported over the forest, is suggested by the fact that contemporary carbon contributed by local biomass burning may not account for total contemporary carbon at the site
Summary
From alpine meadows to stark peaks, Rocky Mountain National Park (RMNP) hosts abundant wildlife, an important water catchment, and roughly 3 million visitors per year (Annual Park Visitation Report, NPS Public Use Statistics Office). Organic compounds contribute the majority of fine-particle mass and attendant visibility impairment at RMNP during summer months (average July 1991–2006 PM2.5 organic mass fraction = 51 ± 6 %, Levin et al, 2009); beyond indications that contemporary carbon (denoting biomass burning and/or biogenic volatile organic carbon (VOC) condensation) and organic nitrogen contribute to organic mass (Benedict et al, 2013a; Schichtel et al, 2008), local organic aerosol (OA) types and sources are unknown. Schurman et al.: Investigating types and sources of OA in Rocky Mountain National Park alizes our developing understanding of atmospheric chemistry Those that do exist indicate a range of particle sources from transported urban particles (e.g., Sun et al, 2009) to biomass burning (e.g., Corrigan et al, 2013) and secondary OA formation involving biogenic VOCs (e.g., Chen et al, 2009); efficient mitigation strategies clearly require a sophisticated understanding of OA sources
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