Sulfur dioxide (SO₂) is an important precursor for the formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO₂ with a minimum limit of detection of 0.75 ppbv (3-$\sigma$) using the spectral range 305.5–312 nm and an averaging time of 5 min. The instrument consists of high-reflectivity mirrors (0.9985 at 310 nm) and a deep UV light source (Light Emitting Diode). The effective absorption path length of the instrument is 610 m with a 0.966 m base length. Published reference absorption cross sections were used to fit and retrieve the SO₂ concentrations and were compared to fluorescence standard measurements for SO₂. The comparison was well correlated, R² = 0.9998 with a correlation slope of 1.04. Interferences for fluorescence measurements were tested and the BBCEAS showed no interference, while ambient measurements responded similarly to standard measurement techniques.

Glyoxal (CHOCHO) is a trace gas in the atmosphere, often used as an indicator of biogenic emissions. It is frequently compared to formaldehyde concentrations, which serve as indicators of anthropogenic emissions, to gain insights into the characteristics of the environmental source. This study employed broadband cavity-enhanced absorption spectroscopy to detect gaseous CHOCHO, methylglyoxal, and NO₂. Two different detection methods are compared. Spectrograph and CCD Detection: This approach involves coupling the system to a spectrograph with a charge-coupled device (CCD) detector. It achieved a 1 min 1-σ detection limit of 2.5 × 10⁸ molecules/cm³, or 10 parts per trillion (ppt). Methylglyoxal and NO₂ achieved 1 min 1-σ detection limits of 34 ppt and 22 ppt, respectively. Interferometer and PMT Detection: In this method, an interferometer is used in conjunction with a photomultiplier tube (PMT) detector. It resulted in a 2 min 1-σ detection limit of 1.5 × 10¹⁰ molecules/cm³, or 600 ppt. The NO₂ 2 min 1-σ detection limit was determined to be 900 ppt. Concentrations of methylglyoxal were difficult to determine using this method, as they appeared to be below the detection limit of the instrument. This study discusses the advantages and limitations of each of these detection methods.

The U.S Environmental Protection Agency’s National Air Toxics Trends Stations Network has been measuring the concentration of hazardous air pollutants (HAPs) including formaldehyde (HCHO) since 2003. Bountiful, Utah (USA) has served as one of the urban monitoring sites since the network was established. Starting in 2013, the mean concentration of HCHO measured in Bountiful, Utah exceeded the non-cancer risk threshold and the 1 in 1 million cancer risk threshold. In addition, the measured concentrations were more than double those found at surrounding locations in Utah. A Positive Matrix Factorization (PMF) analysis using PMF-EPA v5 was performed using historical data (2004–2017) to better understand the sources of formaldehyde in the region. The historical data set included samples that were collected every sixth day on a 24 h basis. Beginning in February 2019 an eight-week air sampling campaign was initiated to measure formaldehyde on a two-hour averaged basis. In addition, the measurements of O_3, NO, NO₂, benzene, toluene, ethylbenzene, and xylenes (BTEX) were also collected. Corresponding back-trajectory wind calculations for selected time periods were calculated to aid in the understanding of the effects of BTEX emission sources and formaldehyde formation. The results indicate that the principal formaldehyde sources are associated with biomass burning and the conversion of biogenic emissions into HCHO. Back-trajectory wind analysis of low (≤3 ppbv) and high (23.8–32.5 ppbv) HCHO cases show a clear dominance of high HCHO originating in trajectories that come from the southwest and pass over the area of the oil refineries and industrial sources in the north Salt Lake City area.

The Wasatch Front in Utah, USA is currently a non-attainment area for ozone according to the Environmental Protection Agency’s (EPA) National Ambient Air Quality Standards (NAAQS). Nitrogen oxides (NO_x = NO₂ + NO) and volatile organic compounds (VOCs) in the presence of sunlight lead to ozone formation in the troposphere. When the rate of oxidant production, defined as the sum of O₃ and NO₂, is faster than the rate of NO_x production, a region is said to be NO_x-limited and ozone formation will be limited by the concentration of NOx species in the region. The inverse of this situation makes the region VOC-limited. Knowing if a region is NO_x-limited or VOC-limited can aid in generating effective mitigation strategies. Understanding the background or regional contributions to ozone in a region, whether it be from the transport of precursors or of ozone, provides information about the lower limit for ozone concentrations that a region can obtain with regulation of local precursors. In this paper, measured oxidant and NO_x concentrations are analyzed from 14 counties in the state of Utah to calculate the regional and local contributions to ozone for each region. This analysis is used to determine the nature of the atmosphere in each county by determining if the region is VOC- or NO_x-limited. Furthermore, this analysis is performed for each county for the years 2012 and 2022 to determine if there has been a change in the oxidative nature and quantify the regional and local contributions to ozone over a 10-year period. All studied counties—except for Washington County—in Utah were found to be VOC-limited in 2012. This shifted in 2022 to most counties being either in a transitional state or being NO_x-limited. Local contributions to ozone increased in two major counties, Cache and Salt Lake Counties, but decreased in Carbon, Davis, Duchesne, Uinta, Utah, Washington, and Weber Counties. Generally, the regional contributions to oxidant concentrations decreased across the state. A summertime spike in both regional and local contributions to oxidants was seen. Smoke from wildfires was seen to increase the regional contributions to oxidants and shift the local regime to be more NO_x-limited.

Air quality is a prevalent concern due to its imposing health risks. The state of Utah, USA, at times over the last 20 years has suffered from some of the worst air quality in the nation. The propensity for the state of Utah to experience elevated concentrations of particulate matter and ozone can in part be attributed to its unique geography that features dry, mountainous topography. Valleys in Utah create ideal environments for extended cold-pool events. In this review, we summarize the research executed in Utah over the past 20 years (2002–2022) by dividing the state into six regions: Utah Valley, Summit County, Southern Utah (regions south of Utah Valley), Cache Valley, Uinta Basin, and Salt Lake Valley. We review the published literature chronologically and provide a summary of each region identifying areas where additional research is warranted. We found that the research effort is weighted towards Uinta Basin and Salt Lake Valley, with the other regions in Utah only adding up to 20% of the research effort. We identified a need for more source apportionment studies, speciated volatile organic compound (VOC) studies, and ozone isopleths. Where ozone isopleths are not able to be created, measurement of glyoxal and formaldehyde concentrations could serve as surrogates for more expensive studies to inform ozone mitigation policies.