scholarly journals Laser Ceilometer Investigation of Persistent Wintertime Cold-Air Pools in Utah’s Salt Lake Valley

2015 ◽  
Vol 54 (4) ◽  
pp. 752-765 ◽  
Author(s):  
Joseph Swyler Young ◽  
C. David Whiteman
Keyword(s):  
Cross Sections ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
Atmospheric Stability ◽  
Experimental Period ◽  
Aerosol Layer ◽  
Mixing Processes ◽  
Cold Air ◽  
Salt Lake Valley ◽  
The Mean

AbstractAs part of the winter 2010/11 Persistent Cold-Air Pool Study in Utah’s Salt Lake Valley, a laser ceilometer was used to continuously measure aerosol-layer characteristics in support of an investigation of the meteorological processes producing the cold-air pools. A surface-based aerosol layer was present during much of the winter. Comparisons were made between ceilometer-measured and visual characteristics of the aerosol layers. A 3–4 January 2011 case study illustrated the meteorological value of time–height backscatter cross sections when used as a base map for meteorological analyses. A variety of meteorological mixing processes were illustrated using ceilometer backscatter data. The mean altitude of the top of the aerosol layer during undisturbed subperiods of the 1 December–7 February experimental period was 1811 m MSL, with a standard deviation of 185 m. The mean aerosol depth was ~500 m AGL in the 1200-m-deep valley. There was surprisingly little variation in the wintertime aerosol layer depth despite large variations in bulk atmospheric stability and ground-based fine particulate matter concentrations.

scholarly journals On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah

2019 ◽  
Vol 19 (14) ◽  
pp. 9287-9308 ◽  
Author(s):  
Erin E. McDuffie ◽  
Caroline C. Womack ◽  
Dorothy L. Fibiger ◽  
William P. Dube ◽  
Alessandro Franchin ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
Ambient Air ◽  
Atmospheric Conditions ◽  
Mixing Processes ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Northern Utah ◽  
Pollution Events

Abstract. Mountain basins in Northern Utah, including the Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PM2.5) can exceed national ambient air quality standards. Previous studies in the SLV have found that PM2.5 is primarily composed of ammonium nitrate (NH4NO3), formed from the condensation of gas-phase ammonia (NH3) and nitric acid (HNO3). Additional studies in several western basins, including the SLV, have suggested that production of HNO3 from nocturnal heterogeneous N2O5 uptake is the dominant source of NH4NO3 during winter. The rate of this process, however, remains poorly quantified, in part due to limited vertical measurements above the surface, where this chemistry is most active. The 2017 Utah Winter Fine Particulate Study (UWFPS) provided the first aircraft measurements of detailed chemical composition during wintertime pollution events in the SLV. Coupled with ground-based observations, analyses of day- and nighttime research flights confirm that PM2.5 during wintertime pollution events is principally composed of NH4NO3, limited by HNO3. Here, observations and box model analyses assess the contribution of N2O5 uptake to nitrate aerosol during pollution events using the NO3- production rate, N2O5 heterogeneous uptake coefficient (γ(N2O5)), and production yield of ClNO2 (φ(ClNO2)), which had medians of 1.6 µg m−3 h−1, 0.076, and 0.220, respectively. While fit values of γ(N2O5) may be biased high by a potential under-measurement in aerosol surface area, other fit quantities are unaffected. Lastly, additional model simulations suggest nocturnal N2O5 uptake produces between 2.4 and 3.9 µg m−3 of nitrate per day when considering the possible effects of dilution. This nocturnal production is sufficient to account for 52 %–85 % of the daily observed surface-level buildup of aerosol nitrate, though accurate quantification is dependent on modeled dilution, mixing processes, and photochemistry.

scholarly journals On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah

2019 ◽  
Author(s):  
Erin E. McDuffie ◽  
Caroline Womack ◽  
Dorothy L. Fibiger ◽  
William P. Dube ◽  
Alessandro Franchin ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
Ambient Air ◽  
Atmospheric Conditions ◽  
Mixing Processes ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Northern Utah ◽  
Pollution Events

Abstract. Mountain basins in Northern Utah, including Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PM2.5) can exceed national ambient air quality standards. Previous studies in SLV have found PM2.5 is primarily composed of ammonium nitrate (NH4NO3), formed from the condensation of gas-phase ammonia (NH3) and nitric acid (HNO3). Additional studies in several western basins, including SLV, have suggested that production of HNO3 from nocturnal heterogeneous N2O5 uptake is the dominant source of NH4NO3 during winter. The rate of this process, however, remains poorly quantified, in part due to limited vertical measurements above the surface, where this chemistry is most active. The 2017 Utah Winter Fine Particulate Study (UWFPS) provided the first aircraft measurements of detailed chemical composition during SLV wintertime pollution events. Coupled with ground-based observations, analysis of day and nighttime research flights confirm that PM2.5 during wintertime pollution events is principally composed of NH4NO3, limited by HNO3. Here, observations and box-model analyses assess the contribution of N2O5 uptake to nitrate aerosol during pollution events using the NO3− production rate, N2O5 heterogeneous uptake coefficient (γ(N2O5)), and production yield of ClNO2 (Φ(ClNO2)), which had medians of 1.6 μg m−3 hr−1, 0.076, and 0.220, respectively. While fit values of γ(N2O5) may be biased high by a potential under-measurement in aerosol surface area, other fit quantities are unaffected. Lastly, additional model simulations suggest nocturnal N2O5 uptake produces 3.9 μg m−3 of nitrate per day, when considering the possible effects of dilution. This nocturnal production is sufficient to account for 86 % of the daily observed surface-level build-up of aerosol nitrate, though accurate quantification is dependent on modeled dilution and mixing processes.

Planetary aerosol electrification: Lessons learned from a terrestrial analogy for Venus

2021 ◽  
Author(s):  
Amethyst Johnson ◽  
Karen Aplin
Keyword(s):  
Atmospheric Stability ◽  
Ionic Mobility ◽  
Mean Free Path ◽  
Lessons Learned ◽  
Lower Atmosphere ◽  
Aerosol Layer ◽  
Electrical Measurements ◽  
Near Surface ◽  
Charged Aerosol ◽  
The Mean

<p>Planetary atmospheric electrification has the potential to damage spacecraft, yet for planets with thick, deep atmospheres such as Venus, the level of electrification remains open to interpretation. Partly due to the difficulty of access and potential hostility to spacecraft, there are limited in-situ observations of deep atmospheres, making terrestrial analogies attractive. One proposed explanation of the observations of near-surface electrification on Venus from sensors on Venera 13 & 14 is a haze of charged aerosol. As the Sahara is an environment with lofted dust that is potentially similar to Venus in terms of atmospheric stability, a simple model was developed estimating a mean aerosol charge based on typical Saharan haze aerosol distributions. Spacecraft surface area and descent speeds were used to estimate the accumulated charge and discharge current measured by the Venera missions, but this model underestimated Venera's electrical measurements by three orders of magnitude. This suggests that an aerosol layer alone cannot explain the charge apparently present in the lower atmosphere of Venus. The simple terrestrial analogy employed may not have been suitable due to the modified pressure and temperature profile affecting the mean free path, ionic mobility and consequently the mean charge. Discrepancies in atmospheric stability and wind patterns must also be evaluated, as the effect of terrestrial wind on aerosol distributions may not be directly applicable to other planets. More detailed calculations of ion-aerosol attachment and re-evaluation of the terrestrial analogy may be able to resolve some these issues, but it looks likely that additional significant sources of charge are required to explain the Venera observations. Triboelectric charging of lofted surface material could exceed charging observed in terrestrial situations, or some unknown atmospheric or non-atmospheric source of charge could have contributed to the Venera electrical measurements. </p>

Simulations of a Cold-Air Pool in Utah’s Salt Lake Valley: Sensitivity to Land Use and Snow Cover

2017 ◽  
Vol 164 (1) ◽  
pp. 63-87 ◽  
Author(s):  
Christopher S. Foster ◽  
Erik T. Crosman ◽  
John D. Horel
Keyword(s):  
Land Use ◽  
Snow Cover ◽  
Salt Lake ◽  
Cold Air ◽  
Salt Lake Valley

scholarly journals The Role of Coarse Aerosol Particles as a Sink of HNO<sub>3</sub> in Wintertime Pollution Events in the Salt Lake Valley

2020 ◽  
Author(s):  
Amy Hrdina ◽  
Jennifer G. Murphy ◽  
Anna Gannet Hallar ◽  
John C. Lin ◽  
Alexander Moravek ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Gas Phase ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
The United States ◽  
Water Soluble ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Coarse Mode ◽  
Pollution Events

Abstract. Wintertime ammonium nitrate (NH4NO3) pollution events burden urban mountain basins around the globe. In the Salt Lake Valley of Utah in the United States, such pollution events are often driven by the formation of persistent cold air pools (PCAP) that trap emissions near the surface for several consecutive days. As a result, secondary pollutants including fine particulate matter less than 2.5 μm in diameter (PM2.5), largely in the form of NH4NO3, build up during these events and lead to severe haze. As part of an extensive measurement campaign to understand the chemical processes underlying PM2.5 formation, the 2017 Utah Winter Fine Particulate Study, water-soluble trace gases and PM2.5 constituents were continuously monitored using the Ambient Ion Monitoring Ion Chromatograph system (AIM-IC) at the University of Utah campus. Gas phase NH3, HNO3, HCl and SO2 along with particulate NH4+, Na+, K+, Mg2+, Ca2+, NO3−, Cl−, and SO42− were measured from January 21 to February 21, 2017. During the two PCAP events captured, the fine particulate matter was dominated by secondary NH4NO3. The comparison of total nitrate (HNO3 + PM2.5 NO3−) and total NHx (NH3 + PM2.5 NH4+) showed NHx was in excess during both pollution events. However, chemical composition analysis of the snowpack during the first PCAP event revealed that the total concentration of deposited NO3− was nearly three times greater than that of deposited NH4+. Daily snow composition measurements showed a strong correlation between NO3− and Ca2+ in the snowpack. The presence of non-volatile salts (Na+, Ca2+, and Mg2+), which are frequently associated with coarse mode dust, was also detected in PM2.5 by the AIM-IC during the two PCAP events, accounting for roughly 5 % of total mass loading. The presence of a significant particle mass and surface area in the coarse mode during the first PCAP event was indicated by size-resolved particle measurements from an Aerodynamic Particle Sizer. Taken together, these observations imply that atmospheric measurements of the gas phase and fine mode particle nitrate may not represent the total burden of nitrate in the atmosphere, implying a potentially significant role for uptake by coarse mode dust. Using the NO3− : NH4+ ratio observed in the snowpack to estimate the proportion of atmospheric nitrate present in the coarse mode, we estimate that the amount of secondary NH4NO3 could double in the absence of the coarse mode sink. The underestimation of total nitrate indicates an incomplete account of the total oxidant production during PCAP events. The ability of coarse particles to permanently remove HNO3 and influence PM2.5 formation is discussed using information about particle composition and size distribution.

The Persistent Cold-Air Pool Study

2013 ◽  
Vol 94 (1) ◽  
pp. 51-63 ◽  
Author(s):  
Neil P. Lareau ◽  
Erik Crosman ◽  
C. David Whiteman ◽  
John D. Horel ◽  
Sebastian W. Hoch ◽  
...  
Keyword(s):  
Salt Lake ◽  
Complete Removal ◽  
Static Stability ◽  
Physical Processes ◽  
Ongoing Research ◽  
Cold Air ◽  
Thermodynamic Structure ◽  
Salt Lake Valley ◽  
University Of Utah ◽  
Strong Winds

The Persistent Cold-Air Pool Study (PCAPS) was conducted in Utah's Salt Lake valley from 1 December 2010 to 7 February 2011. The field campaign's primary goal was to improve understanding of the physical processes governing the evolution of multiday cold-air pools (CAPs) that are common in mountain basins during the winter. Meteorological instrumentation deployed throughout the Salt Lake valley provided observations of the processes contributing to the formation, maintenance, and destruction of 10 persistent CAP episodes. The close proximity of PCAPS field sites to residences and the University of Utah campus allowed many undergraduate and graduate students to participate in the study. Ongoing research, supported by the National Science Foundation, is using the PCAPS dataset to examine CAP evolution. Preliminary analyses reveal that variations in CAP thermodynamic structure are attributable to a multitude of physical processes affecting local static stability: for example, synoptic-scale processes impact changes in temperatures and cloudiness aloft while variations in boundary layer forcing modulate the lower levels of CAPs. During episodes of strong winds, complex interactions between the synoptic and mesoscale f lows, local thermodynamic structure, and terrain lead to both partial and complete removal of CAPs. In addition, the strength and duration of CAP events affect the local concentrations of pollutants such as PM2.5.

scholarly journals Temperature Inversion and Ultrafine Particulate/Near Ultrafine Particulate Matter Concentrations in the Salt Lake Valley

2021 ◽  
Vol 2 (7) ◽  
pp. 422-435
Author(s):  
Danielle Mecate ◽  
Rod Handy ◽  
Leon Pahler ◽  
Darrah Sleeth ◽  
Joemy Ramsay ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Health Outcomes ◽  
Salt Lake ◽  
Temperature Inversion ◽  
Linear Regression Models ◽  
Salt Lake Valley ◽  
Adverse Health Outcomes ◽  
The Mean ◽  
Ultrafine Particulate Matter ◽  
Negative Health Outcomes

Ultrafine particulate (UFP) matter exposures are associated with negative health outcomes. UFPs (<100nm) and near UFP (NUFP) matter (4.5nm - 250nm) are trapped by the bowl-like geography of the Salt Lake Valley causing winter inversions (i.e., trapped particulate matter (PM)). Enmont PUFP C100 and Grimm 1.109 particle counters were used to define NUFP concentrations during inversion (n=5) and non-inversion (n=5) days at 7 sites. NUFP concentrations served as a proxy for the UFP fraction. NUFP concentrations were log-transformed and multivariable mixed effects linear regression models determined if NUFP concentration differed between inversion and non-inversion or by length of inversion. Difference in fraction NUFP was also analyzed. The mean NUFP concentration was 1.49-fold higher during inversions (95% CI 1.11–2.02), whereas the fraction declined by 0.22 (95% CI -0.31– -0.13). Increased NUFP concentrations during inversions may lead to increased adverse health outcomes. These findings have serious implications for inversion-prone regions.

scholarly journals The role of coarse aerosol particles as a sink of HNO<sub>3</sub> in wintertime pollution events in the Salt Lake Valley

2021 ◽  
Vol 21 (10) ◽  
pp. 8111-8126
Author(s):  
Amy Hrdina ◽  
Jennifer G. Murphy ◽  
Anna Gannet Hallar ◽  
John C. Lin ◽  
Alexander Moravek ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Gas Phase ◽  
Salt Lake ◽  
Fine Particulate Matter ◽  
The United States ◽  
Water Soluble ◽  
Salt Lake Valley ◽  
Fine Particulate ◽  
Coarse Mode ◽  
Pollution Events

Abstract. Wintertime ammonium nitrate (NH4NO3) pollution events burden urban mountain basins around the globe. In the Salt Lake Valley of Utah in the United States, such pollution events are often driven by the formation of persistent cold-air pools (PCAPs) that trap emissions near the surface for several consecutive days. As a result, secondary pollutants including fine particulate matter less than 2.5 µm in diameter (PM2.5), largely in the form of NH4NO3, build up during these events and lead to severe haze. As part of an extensive measurement campaign to understand the chemical processes underlying PM2.5 formation, the 2017 Utah Winter Fine Particulate Study, water-soluble trace gases and PM2.5 constituents were continuously monitored using the ambient ion monitoring ion chromatograph (AIM-IC) system at the University of Utah campus. Gas-phase NH3, HNO3, HCl, and SO2 along with particulate NH4+, Na+, K+, Mg2+, Ca2+, NO3-, Cl−, and SO42- were measured from 21 January to 21 February 2017. During the two PCAP events captured, the fine particulate matter was dominated by secondary NH4NO3. The comparison of total nitrate (HNO3 + PM2.5 NO3-) and total NHx (NH3 + PM2.5 NH4+) showed NHx was in excess during both pollution events. However, chemical composition analysis of the snowpack during the first PCAP event revealed that the total concentration of deposited NO3- was nearly 3 times greater than that of deposited NH4+. Daily snow composition measurements showed a strong correlation between NO3- and Ca2+ in the snowpack. The presence of non-volatile salts (Na+, Ca2+, and Mg2+), which are frequently associated with coarse-mode dust, was also detected in PM2.5 by the AIM-IC during the two PCAP events, accounting for roughly 5 % of total mass loading. The presence of a significant particle mass and surface area in the coarse mode during the first PCAP event was indicated by size-resolved particle measurements from an aerodynamic particle sizer. Taken together, these observations imply that atmospheric measurements of the gas-phase and fine-mode particle nitrate may not represent the total burden of nitrate in the atmosphere, implying a potentially significant role for uptake by coarse-mode dust. Using the NO3- : NH4+ ratio observed in the snowpack to estimate the proportion of atmospheric nitrate present in the coarse mode, we estimate that the amount of secondary NH4NO3 could double in the absence of the coarse-mode sink. The underestimation of total nitrate indicates an incomplete account of the total oxidant production during PCAP events. The ability of coarse particles to permanently remove HNO3 and influence PM2.5 formation is discussed using information about particle composition and size distribution.

Coupling between Chemical and Meteorological Processes under Persistent Cold-Air Pool Conditions: Evolution of Wintertime PM2.5 Pollution Events and N2O5 Observations in Utah’s Salt Lake Valley

2017 ◽  
Vol 51 (11) ◽  
pp. 5941-5950 ◽  
Author(s):  
Munkhbayar Baasandorj ◽  
Sebastian W. Hoch ◽  
Ryan Bares ◽  
John C. Lin ◽  
Steven S. Brown ◽  
...  
Keyword(s):  
Salt Lake ◽  
Cold Air ◽  
Salt Lake Valley ◽  
Pollution Events

scholarly journals Surface Turbulent Fluxes during Persistent Cold-Air Pool Events in the Salt Lake Valley, Utah. Part I: Observations

2019 ◽  
Vol 58 (12) ◽  
pp. 2553-2568 ◽  
Author(s):  
Xia Sun ◽  
Heather A. Holmes
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Land Surface ◽  
Salt Lake ◽  
Turbulent Fluxes ◽  
Neutral Stability ◽  
Stability Range ◽  
Cold Air ◽  
Salt Lake Valley ◽  
Ground Heat Flux

AbstractThe land surface is coupled to the atmospheric boundary layer through surface turbulent fluxes. Persistent cold-air pools (PCAPs) form in topographic depressions where cold, dense air fills the valley basin and in the presence of air pollution is accompanied by poor air quality. For the first time, the surface turbulence dataset from seven monitors during the Persistent Cold-Air Pool Study conducted in Salt Lake Valley, Utah (December 2010–February 2011), are analyzed. We found that the surface sensible (H) and latent (LE) heat fluxes were lower during strong PCAP events compared with non-PCAPs. The higher ratio of heat flux to net radiation (H/Rn and LE/Rn) for strong PCAPs compared with weak PCAPs is suspected to be related to the presence of boundary layer clouds, which could enhance the turbulent mixing through cloud top–down mixing. The daily average ground heat flux (G) was a similar order of magnitude to H and LE during wintertime. The highest surface turbulent fluxes and energy balance closure occurred in the stability range of −0.05 < ξ ≤ −0.02, or under slightly unstable conditions, near the neutral stability range. The median surface exchange coefficient (Ch), a crucial parameter to determine surface turbulent fluxes in land surface models, was slightly higher at the bare land site (BL) than the short vegetation sites (PH and CR) in wintertime, suggesting the importance of dynamic land-use information in numerical models.

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