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Dinosaur National Monument (DINO) is located near the northeastern edge of the Uinta Basin and often experiences elevated levels of wintertime ground-level ozone. Previous studies have shown that high ozone mixing ratios in the Uinta Basin are driven by elevated levels of volatile organic compounds (VOCs) and nitrogen oxides (NO x ) from regional oil and gas development coupled with temperature inversions and enhanced photochemistry from persistent snow cover. Here, we show that persistent snow cover and temperature inversions, along with abundant ammonia, also lead to wintertime haze in this region. A study was conducted at DINO from November 2018 through May 2020 where ozone, speciated fine and coarse aerosols, inorganic gases, and VOCs were measured. Three National Ambient Air Quality Standards (NAAQS) ozone exceedances were observed in the first winter, and no exceedances were observed in the second winter. In contrast, elevated levels of particulate matter were observed both winters, with 24-h averaged particle light extinction exceeding 100 Mm -1 . These haze events were dominated by ammonium nitrate, and particulate organics were highly correlated with ammonium nitrate. Ammonium nitrate formation was limited by nitric acid in winter. As such, reductions in regional NO x emissions should reduce haze levels and improve visibility at DINO in winter. Long-term measurements of particulate matter from nearby Vernal, Utah, suggest that visibility impairment is a persistent issue in the Uinta Basin in winter. From April through October 2019, relatively clean conditions occurred, with average particle extinction of ~10 Mm -1 . During this period, ammonium nitrate concentrations were lower by more than an order of magnitude, and contributions from coarse mass and soil to haze levels increased. VOC markers indicated that the high levels of observed pollutants in winter were likely from local sources related to oil and gas extraction activities. Implications : Elevated ground-level ozone and haze levels were observed at Dinosaur National Monument in winter. Haze episodes were dominated by ammonium nitrate, with 24-h averaged particle light extinction exceeding 100 Mm -1 , reducing visual range near the surface to ~35 km. Despite elevated ammonium nitrate concentrations, additional gas-phase ammonia was available, such that any increase in NO x emissions in the region is likely to lead to even greater haze levels.

The Clean Air Action implemented by the Chinese government in 2013 has greatly improved air quality in the North China Plain (NCP). In this work, we report changes in the chemical components of atmospheric fine particulate matter (PM 2.5 ) at four NCP sampling sites from 2012/2013 to 2017 to investigate the impacts and drivers of the Clean Air Action on aerosol chemistry, especially for secondary inorganic aerosols (SIA). During the observation period, the concentrations of PM 2.5 and its chemical components (especially SIA, organic carbon (OC), and elemental carbon (EC)) and the frequency of polluted days (daily PM 2.5 concentration ≥ 75 μg m -3 ) in the NCP, declined significantly at all four sites. Asynchronized reduction in SIA components (large decreases in SO 4 2- with stable or even increased NO 3 - and NH 4 + ) was observed in urban Beijing, revealing a shift of the primary form of SIA, which suggested the fractions of NO 3 - increased more rapidly than SO 4 2- during PM 2.5 pollution episodes, especially in 2016 and 2017. In addition, unexpected increases in the sulfur oxidation ratio (SOR) and the nitrogen oxidation ratio (NOR) were observed among sites and across years in the substantially decreased PM 2.5 levels. They were largely determined by secondary aerosol precursors (i.e. decreased SO 2 and NO 2 ), photochemical oxidants (e.g. increased O 3 ), temperature, and relative humidity via gas-phase and heterogeneous reactions. Our results not only highlight the effectiveness of the Action Plan for improving air quality in the NCP, but also suggest an increasing importance of SIA in determining PM 2.5 concentration and composition., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Abstract: Considerable effort has been put into characterizing the ionic composition of fogs and clouds over the past twenty-five years. Recently it has become evident that clouds and fogs often contain large concentrations of organic material as well. Here we report findings from a series of studies examining the organic composition of radiation fogs in central California. Organic compounds in these fogs comprise a major fraction of total solute mass, with total organic carbon sometimes reaching levels of several tens of mg/L. This organic matter is comprised of a wide variety of compounds, ranging from low molecular weight organic acids to high molecular weight compounds with molecular masses approaching several hundred to a thousand g/mole. The most abundant individual compounds are typically formic acid, acetic acid, and formaldehyde. High concentrations are also observed of some dicarboxylic acids (e.g., oxalate) and dicarbonyls (e.g., glyoxal and methylglyoxal) and of levoglucosan, an anhydrosugar characteristically emitted by biomass combustion. Many other compounds have been identified in fog water by GC/MS, including long chain n-alkanoic acids, n-alkanes, PAH, and others, although these compounds typically comprise a total of only a few percent of fog TOC. Measurements of fog scavenging of organic and elemental carbon reveal preferential scavenging of organic carbon. Tracking of individual organic compounds utilized as source type markers suggests the fogs differentially scavenge carbonaceous particles from different source types, with more active processing of wood smoke than vehicle exhaust. Observations of high deposition velocities of fog-borne organic carbon, in excess of 1 cm/s, indicate that fogs in the region represent an important mechanism for cleansing the atmosphere of pollution. [Copyright &y& Elsevier]

Exposure to particulate air pollution is a major cause of mortality and morbidity worldwide. In developing countries, the combustion of solid fuels is widely used as a source of energy, and this process can produce exposure to harmful levels of particulate matter with diameters smaller than 2.5 microns (PM2.5). However, as countries develop, solid fuel may be replaced by centralized coal combustion, and vehicles burning diesel and gasoline may become common, changing the concentration and composition of PM2.5, which ultimately changes the population health effects. Therefore, there is a continuous need for in-situ monitoring of air pollution in developing nations, both to estimate human exposure and to monitor changes in air quality. In this study, we present measurements from a 5-week field experiment in Palapye, Botswana. We used a low-cost, highly portable instrument package to measure surface-based aerosol optical depth (AOD), real-time surface PM2.5 concentrations using a third-party optical sensor, and time-integrated PM2.5 concentration and composition by collecting PM2.5 onto Teflon filters. Furthermore, we employed other low-cost measurements of real-time black carbon and time-integrated ammonia to help interpret the observed PM2.5 composition and concentration information during the field experiment. We found that the average PM2.5 concentration (9.5 µg∙m−3) was below the World Health Organization (WHO) annual limit, and this concentration closely agrees with estimates from the Global Burden of Disease (GBD) report estimates for this region. Sulfate aerosol and carbonaceous aerosol, likely from coal combustion and biomass burning, respectively, were the main contributors to PM2.5 by mass (33% and 27% of total PM2.5 mass, respectively). While these observed concentrations were on average below WHO guidelines, we found that the measurement site experienced higher concentrations of aerosol during first half our measurement period (14.5 µg∙m−3), which is classified as "moderately unhealthy" according to the WHO standard. [ABSTRACT FROM AUTHOR]

Abstract: While fog and cloud composition has been studied for decades, most of the research was limited to inorganic species and fog acidity. Recently the focus has shifted towards organic matter in the atmospheric aqueous phase of fogs and clouds: its origin, reactivity and fate. An impressive number of fog and cloud chemistry observational studies have been performed over the last decade throughout the world. In the present work we will review the state of knowledge of atmospheric organic matter processing by fogs, with a focus on field observations. We start by reviewing observational studies in general and then discuss our knowledge on the occurrence of organic matter in fogs, its solubility, characterization and molecular speciation. Organic carbon concentrations can vary widely from approximately 1mgC/L in remote marine environments to more than 100mgC/L in polluted radiation fogs, accounting for a substantial part of fogwater solutes. The carbonaceous material can enter the droplets from the gas and particle phase and the scavenging behavior of fogs will be detailed. Observational studies showed evidence of aqueous phase transformation of organic material, in particular secondary organic aerosol (SOA) generation, in fog. Recent observations of biological material in fog suggest also an impact of biological processing within the droplets on fog organic matter. The review will end with a discussion of the impact of fog on the deposition fluxes of organic material and hence its atmospheric lifetime. [Copyright &y& Elsevier]

Abstract: Cloud/fog samples were collected during spring of 2007 in the highly polluted North China Plain in order to examine the impact of pollution and dust particles on cloud water chemistry. The volume weighted mean pH of cloud water was 3.68. The cloud acidity was shown to be associated with air mass origins. Cloud water with its air mass trajectories originating from the southern part of China was more acidic than those from northern China. Anthropogenic source and dust had obvious impact on cloud water composition as indicated by the very high mean concentrations of SO4 2− (1331.65μeqL−1), NO3 − (772.44μeqL−1), NH4 + (1375.92μeqL−1) and Ca2+ (625.81μeqL−1) in the observation periods. During sandstorm days, cloud pH values were relatively high, and the concentrations of all the ions in cloud water reached unusual high levels. Significant decreases in the mass concentrations of PM2.5 and PM10 were observed during cloud events. The average scavenging ratio for PM2.5 and PM10 was 52.0% and 55.7%, respectively. Among the soluble ions in fine particles, NO3 −, K+ and NH4 + tend to be more easily scavenged than Ca2+ and Na+. [Copyright &y& Elsevier]

Abstract: The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS), conducted during the spring and summer of 2006, was designed to assess the sources of nitrogen and sulfur species that contribute to wet and dry deposition and visibility impairment at Rocky Mountain National Park (RMNP), Colorado. Several source apportionment methods were utilized for RoMANS, including the Trajectory Mass Balance (TrMB) Model, a receptor-based method in which the hourly measured concentrations are the dependent variables and the residence times of back trajectories in several source regions are the independent variables. The regression coefficients are estimates of the mean emissions, dispersion, chemical transformation, and deposition between the source areas and the receptors. For RoMANS, a new ensemble technique was employed in which input parameters were varied to explore the range, variability, and model sensitivity of source attribution results and statistical measures of model fit over thousands of trials for each set of concentration measurements. Results showed that carefully chosen source regions dramatically improved the ability of TrMB to reproduce temporal patterns in the measured concentrations, and source attribution results were also very sensitive to source region choices. Conversely, attributions were relatively insensitive to trajectory start height, trajectory length, minimum endpoints per source area, and maximum endpoint height, as long as the trajectories were long enough to reach contributing source areas and were not overly restricted in height or horizontal location. Source attribution results estimated that more than half the ammonia and 30–45% of sulfur dioxide and other nitrogen-containing species at the RoMANS core site were from sources within the state of Colorado. Approximately a quarter to a third of the sulfate was from within Colorado. [ABSTRACT FROM AUTHOR]

Abstract: Fogwater and air samples were collected in Baton Rouge between November 2004–February 2005 and during February 2006 at Houston. Organic compounds present in the fog samples were detected, quantified and then grouped into different compound classes based on molecular size, solubility and polarity using gas chromatography/mass spectrometry, high performance liquid chromatography with diode array detection and ion chromatography. Organic compounds were grouped as n-alkanes, aromatics and polycyclic aromatics, carbonyls, alcohols, amides and esters. Organic compounds in fog and air samples in Houston indicated clear urban/industrial anthropogenic origin, while compounds detected in Baton Rouge fog and air samples showed a mix of both agricultural and urban/industrial anthropogenic inputs. Among the various polycyclic aromatic compounds detected, the total concentration of naphthalene and its derivatives was 2.8 μg m−3 in Houston and 0.08 μg m−3 in Baton Rouge air. Analysis of concentrations of organic compounds pre- and post- fog revealed that compounds with low vapor pressure had higher scavenging efficiency in fog sampled at the two locations. Concentrations of organic compounds in fog samples were higher than those predicted by conventional air-water Henry''s law equilibrium. Observed higher concentrations in the aqueous phase were modeled accounting for surface adsorption and accumulation of gas phase species and the presence of humic-like substances in fogwater. [Copyright &y& Elsevier]

Fog samples were collected in two population centers of the US Gulf Coast (Houston, Texas and Baton Rouge, Louisiana) using Caltech active strand cloud collectors. A total of 32 fogwater samples were collected in Baton Rouge (November 2004–February 2005) and Houston (February 2006). These samples were analyzed for pH, total and dissolved organic carbon, major inorganic ions, and a variety of organic compounds including organic acids, aromatics, carbonyls, and linear alkanes. Fogs in both environments were of moderate density, with typical fog liquid water contents <100mgm−3. Fog samples collected in Houston reflect a clear influence of marine and anthropogenic inputs, while Baton Rouge samples also reflect agricultural inputs. The volume-weighted mean fog pH was somewhat more acidic (∼4.3) in Houston than in Baton Rouge (∼5.0). A wide pH range was observed in fog at both locations. Houston fog had higher concentrations of Cl−, NO3 −, Na+, Mg2+, and Ca2+. Sulfate to nitrate ratios were high in fogs at both locations, typical of many clouds in the eastern US. Total organic carbon concentrations were much higher in Houston fogs than in Baton Rouge fogs. Efforts to speciate dissolved organic carbon (DOC) reveal large contributions from organic acids and carbonyls, with smaller contributions from other organic compound families including aromatics, alkanes, amides, and alcohols. Approximately 40% of the fog DOC was unspeciated in samples from both study locations. [Copyright &y& Elsevier]

Abstract: Observations of aerosol physical, chemical, and optical properties made at 38 locations in Washington, Oregon, and California are presented to show the regional-scale influence of wildfire smoke during the summer of 2002. Aerosol measurements made during an intensive field campaign conducted in July, August, and September 2002 in Yosemite National Park indicated that smoke-impacted aerosols were present at the park during frequent haze episodes. In addition, backward trajectory analyses showed that large-scale meteorological conditions during the study were dominated by transport from western and southern Oregon, a region with high fire activity during the summer of 2002. Observations of aerosol properties at the Yosemite NP site were remarkably similar, with similar temporal variations, to data from a second monitoring site at Blodgett Forest Research Station in the Sierra Nevada, approximately 150km to the NNW. Further similarities to the temporal changes in aerosol properties as measured by monitoring networks with numerous sites in California and Oregon confirmed the regional nature of the haze, which had elevated fine aerosol particle mass concentrations compared with typical summertime average concentrations. The observations suggest that emissions from wild fires can have strong and sustained regional impacts on aerosol concentrations, air quality, and visibility. [Copyright &y& Elsevier]

The National Park Service is tasked with protecting the lands it oversees, including from impacts from air pollutants. While ozone is regularly monitored in many parks across the United States, precursors to ozone formation are not routinely measured. In this work we characterize volatile organic compounds (VOCs) at four national parks in the southwestern United States: Carlsbad Caverns (CAVE), Great Basin (GRBA), Grand Canyon (GRCA), and Joshua Tree (JOTR). Whole air samples were collected for VOC analysis for five months (mid-April through mid-September) in 2017. Samples were collected from 3 p.m. to 5 p.m. local time, corresponding approximately to the time of expected peak ozone concentrations, and were analyzed using gas chromatography for a variety of compounds including alkanes, alkenes, aromatics, biogenics, and alkyl nitrates. Among the four parks, the total measured VOC mixing ratio was greatest at CAVE, mostly due to an abundance of light alkanes (on average 94% of all VOCs measured) from oil and gas sources. VOC concentrations at the other three parks were similar to each other and approximately 7–10 times lower than at CAVE. While VOC sources varied across sites, VOC-OH reactivity was dominated by biogenic compounds at all sites except CAVE, which had similar contributions from biogenics and from light alkanes. JOTR had the highest levels of ozone, and the highest concentrations of biogenic VOCs among the parks studied. Back trajectory analysis suggests that the high levels of ozone occurred when air flow came from the west, in the direction of the greater Los Angeles area. The two parks most removed from oil and gas and urban sources, GRBA and GRCA, had the lowest concentrations of total VOCs, and were likely influenced by long range transport of pollutants. To better characterize source influences at the park with the highest VOC concentrations, intensive measurements were conducted in and around CAVE for one week in September 2017. These measurements showed an oil and gas influence throughout the region and indicated that the whole air samples collected over the five-month study did not capture the full range of VOC mixing ratios present at other times of the day. • VOC were measured at Carlsbad Caverns, Great Basin, Grand Canyon, and Joshua Tree National Parks. • CAVE had the highest levels of light alkanes, by approximately an order of magnitude. • VOC concentrations at the other three parks were similar to each other. • Measurements in and around CAVE showed an oil and gas influence. [ABSTRACT FROM AUTHOR]