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Storm Peak Laboratory, located on the Steamboat Springs Ski Resort in Colorado on the west summit of Mount Werner at 10 532 ft (3220 m) MSL, is an internationally recognized high-elevation atmospheric research station that has been in use for over 40 years. This article provides a brief history of the Storm Peak Laboratory and the major research themes it has supported and discusses opportunities to leverage mountain observatory measurements to advance our understanding of the atmospheric processes. This facility provides long-term measurements of meteorology, clouds, aerosols, snow hydrology, and atmospheric gases, and it serves as a “proving ground” for instrument development and testing. Storm Peak Laboratory is part of multiple national and international observational networks. Due to the unique capabilities of Storm Peak Laboratory, there is a long history of targeted field campaigns primarily within the following research areas: mixed-phase cloud microphysics; atmospheric chemistry pertaining to the formation, characterization, and hygroscopicity of aerosols; and the transport and transformation of atmospheric mercury. Research training has been central to the mission of Storm Peak Laboratory (SPL) over the last 40 years. Currently, SPL hosts both undergraduate- and graduate-level courses in atmospheric science and snow hydrology organized by numerous institutions. Examples of these unique research training opportunities are provided. 

Abstract. Mercury (Hg) is a global atmospheric pollutant. In its oxidized form (HgII), it can readily deposit to ecosystems, where it may bioaccumulate and cause severe health effects. High HgII concentrations are reported in the free troposphere, but spatiotemporal data coverage is limited. Underestimation of HgII by commercially available measurement systems hinders quantification of Hg cycling and fate. During spring–summer 2021 and 2022, we measured elemental (Hg0) and oxidized Hg using a calibrated dual-channel system alongside trace gases, aerosol properties, and meteorology at the high-elevation Storm Peak Laboratory (SPL) above Steamboat Springs, Colorado. Oxidized Hg concentrations displayed diel and episodic behavior similar to previous work at SPL but were approximately 3 times higher in magnitude due to improved measurement accuracy. We identified 18 multi-day events of elevated HgII (mean enhancement of 36 pg m−3) that occurred in dry air (mean ± SD of relative humidity = 32 ± 16 %). Lagrangian particle dispersion model (HYSPLIT–STILT, Hybrid Single-Particle Lagrangian Integrated Trajectory–Stochastic Time-Inverted Lagrangian Transport) 10 d back trajectories showed that the majority of transport prior to events occurred in the low to middle free troposphere. Oxidized Hg was anticorrelated with Hg0 during events, with an average (± SD) slope of −0.39 ± 0.14. We posit that event HgII resulted from upwind oxidation followed by deposition or cloud uptake during transport. Meanwhile, sulfur dioxide measurements verified that three upwind coal-fired power plants did not influence ambient Hg at SPL. Principal component analysis showed HgII consistently inversely related to Hg0 and generally not associated with combustion tracers, confirming oxidation in the clean, dry free troposphere as its primary origin. 

Abstract. New particle formation (NPF) events are defined as asudden burst of aerosols followed by growth and can impact climate bygrowing to larger sizes and under proper conditions, potentially formingcloud condensation nuclei (CCN). Field measurements relating NPF and CCN arecrucial in expanding regional understanding of how aerosols impactclimate. To quantify the possible impact of NPF on CCN formation, it isimportant to not only maintain consistency when classifying NPF events butalso consider the proper timeframe for particle growth to CCN-relevantsizes. Here, we analyze 15 years of direct measurements of both aerosol sizedistributions and CCN concentrations and combine them with novel methods toquantify the impact of NPF on CCN formation at Storm Peak Laboratory (SPL),a remote, mountaintop observatory in Colorado. Using the new automaticmethod to classify NPF, we find that NPF occurs on 50 % of all daysconsidered in the study from 2006 to 2021, demonstrating consistency withprevious work at SPL. NPF significantly enhances CCN during the winter by afactor of 1.36 and during the spring by a factor of 1.54, which, when combined withprevious work at SPL, suggests the enhancement of CCN by NPF occurs on aregional scale. We confirm that events with persistent growth are common inthe spring and winter, while burst events are more common in the summer andfall. A visual validation of the automatic method was performed in thestudy. For the first time, results clearly demonstrate the significantimpact of NPF on CCN in montane North American regions and the potential forwidespread impact of NPF on CCN. 

Abstract. A new inlet for studying the aerosol particles andhydrometeor residuals that compose mixed-phase clouds – the phaSeseParation Inlet for Droplets icE residuals and inteRstitial aerosolparticles (SPIDER) – is described here. SPIDER combines a large pumpedcounterflow virtual impactor (L-PCVI), a flow tube evaporation chamber, anda pumped counterflow virtual impactor (PCVI) to separate droplets, icecrystals (∼3–25 µm), and interstitial aerosolparticles for simultaneous sampling. Laboratory verification tests of eachindividual component and the composite SPIDER system were conducted.Transmission efficiency, evaporation, and ice crystals' survival weredetermined to show the capability of the system. The experiments show theSPIDER system can separate distinct cloud elements and interstitial aerosolparticles for subsequent analysis. As a field instrument, SPIDER will helpexplore the properties of different cloud elements and interstitial aerosolparticles in mixed-phase clouds. 

Abstract Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical-meteorological interactions that drive high pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in Western U.S. basins. Approximately 120 people participated, representing 50 institutions and 5 countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary-layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological-chemical linkages outlined here, nor to validate complex processes within coupled atmosphere-chemistry models.