Summer ozone concentrations in the vicinity of the Great Salt Lake

Abstract

Residents near the Great Salt Lake in northern Utah, USA have been exposed to ozone levels during recent summers exceeding the current United States National Ambient Air Quality Standard. Accurately forecasting those exceedances has been difficult as a result of the complex meteorological and photochemical processes fostering them. To help improve such forecasts, a low-cost field study was conducted during summer 2015 to provide comprehensive observations of boundary-layer ozone concentrations in the context of the prevailing meteorological conditions. A network of surface ozone sensors was supplemented by sensors mounted on vehicles, a public transit light-rail car, news helicopter, tethered sonde, and unmanned aerial vehicle. The temporal and spatial evolution of boundary-layer ozone concentrations were compared with the prevailing regional and local meteorological conditions on the basis of gridded operational analyses, surface weather stations, and additional sensors deployed for the field study. High ozone concentrations during June 2015 resulted primarily from local processes while smoke transported from distant wildfires contributed to elevated ozone concentrations during August. The Great Salt Lake influenced ozone concentrations along the Wasatch Front through several mechanisms, most importantly its impact on local wind circulations. The highest ozone concentrations were often found in a narrow zone between the Great Salt Lake and the urban regions to its south and east. Observations from multiple fixed site and mobile platforms during 18-19 August illustrate the complex variations in ozone concentrations as a function of elevation at the surface as well as vertically through the deep boundary layer.

The TRAX Light-Rail Train Air Quality Observation Project

“…Ground-level particulate matter becomes trapped for up to two weeks when winter cold-air pools are present that result from stable conditions aloft and cold air near the snow-covered ground [2]. During long summer days, clear skies and light winds contribute to favorable conditions for elevated photochemical production and accumulation of ground level ozone [3]. Smoke from local wildfires, as well as those throughout the western United States, can significantly enhance ozone concentrations in the SLV, while at the same time increasing particulate concentrations [4].…”

“…Smoke from local wildfires, as well as those throughout the western United States, can significantly enhance ozone concentrations in the SLV, while at the same time increasing particulate concentrations [4]. Complex spatial and temporal variability in pollutants within the SLV is driven by terrain-flow interactions as well as urban chemistry [3][4][5][6][7][8].…”

“…Numerous studies have focused on wintertime elevated PM 2.5 levels in the SLV [5,19] while only a few have focused on elevated summertime ozone levels [2,3]. Field campaigns during recent winters have studied air pollution within periods ranging from several weeks to several months along the Wasatch Front.…”

“…The second sensor (RAIL1) was placed on a UTA service shed located approximately three meters from the rail line at a location where inlet effects might be a factor, since the trains are typically moving at 85 km/h in that location. The FEM ozone sensors are not subject to the train motion and inlet effects, and thus no ground validation sites were needed for ozone, as ground-based stationary [41], ground-based mobile [3], and aircraft-based campaigns have used this sensor [42]. These sensors were maintained and calibrated monthly to ensure accurate ozone data collection.…”

Modeling net effects of transit operations on vehicle miles traveled, fuel consumption, carbon dioxide, and criteria air pollutant emissions in a mid-size US metro area: findings from Salt Lake City, UT

“…During the winter, meteorological 'inversion' events with warmer air sitting on top of cooler air suppress atmospheric mixing and trap pollutants within the valley, leading to high levels of fine particulate matter (PM 2.5 ) (Bares et al 2018). During the summer, elevated levels of ozone are a regular occurrence (Horel et al 2016). Health concern for this large urban population motivates the question we seek to address in this paper: what are UTA's actual and potential impacts on air quality in the SLV airshed?…”