Effects of Molecular-Level Compositional Variability in Organic Aerosol on Phase State and Thermodynamic Mixing Behavior.

The molecular-level composition and structure of organic aerosol (OA) affect its chemical/physical properties, transformations, and impacts. Here, we use the molecular-level chemical composition of functionalized OA from three diverse field sites to evaluate the effect of molecular-level compositional variability on OA phase state and thermodynamic mixing favorability. For these ambient sites, modeled aerosol phase state ranges from liquid to semisolid. The observed variability in OA composition has some effect on resulting phase state, but other factors like the presence of inorganic ions, aerosol liquid water, and internal versus external mixing with water are determining factors in whether these particles exist as liquids, semisolids, or solids. Organic molecular composition plays a more important role in determining phase state for phase-separated (verus well-mixed) systems. Similarly, despite the observed OA compositional differences, the thermodynamic mixing favorability for OA samples with aerosol liquid water, isoprene oxidation products, or monoterpene oxidation products remains fairly consistent within each campaign. Mixing of filter-sampled OA and isoprene or monoterpene oxidation products is often favorable in both seasons, while mixing with water is generally unfavorable.

A large-scale investigation of the quality of groundwater in six major districts of Central India during the 2010-2011 sampling campaign.

This paper investigates the groundwater quality in six major districts of Madhya Pradesh in central India, namely, Balaghat, Chhindwara, Dhar, Jhabua, Mandla, and Seoni during the 2010-2011 sampling campaign, and discusses improvements made in the supplied water quality between the years 2011 and 2017. Groundwater is the main source of water for a combined rural population of over 7 million in these districts. Its contamination could have a huge impact on public health. We analyzed the data collected from a large-scale water sampling campaign carried out by the Public Health Engineering Department (PHED), Government of Madhya Pradesh between 2010 and 2011 during which all rural tube wells and dug wells were sampled in these six districts. Eight hundred thirty-one dug wells and 47,606 tube wells were sampled in total and were analyzed for turbidity, hardness, iron, nitrate, fluoride, chloride, and sulfate ion concentrations. Our study found water in 21 out of the 228 dug wells in Chhindwara district unfit for drinking due to fluoride contamination while all dug wells in Balaghat had fluoride within the permissible limit. Twenty-six of the 56 dug wells and 4825 of the 9390 tube wells in Dhar district exceeded the permissible limit for nitrate while 100% dug wells in Balaghat, Seoni, and Chhindwara had low levels of nitrate. Twenty-four of the 228 dug wells and 1669 of 6790 tube wells in Chhindwara had high iron concentration. The median pH value in both dug wells and tube wells varied between 6 and 8 in all six districts. Still, a significant number of tube wells exceeded a pH of 8.5 especially in Mandla and Seoni districts. In conclusion, this study shows that parts of inhabited rural Madhya Pradesh were potentially exposed to contaminated subsurface water during 2010-2011. The analysis has been correlated with rural health survey results wherever available to estimate the visible impact. We next highlight that the quality of drinking water has enormously improved since 2011 in all six districts as a result of rigorous treatment of extracted subsurface water on the ground before supplying to rural habitations as well as efficient distribution from healthy wells. Our research could provide impetus to the state government to develop innovative solutions for improving groundwater quality in these areas as existing solutions are largely protective techniques. We have identified specific ions responsible for groundwater contamination in different districts which would allow the development of district specific effective mitigation strategies.

Total organic carbon measurements reveal major gaps in petrochemical emissions reporting.

Anthropogenic organic carbon emissions reporting has been largely limited to subsets of chemically speciated volatile organic compounds. However, new aircraft-based measurements revealed total gas-phase organic carbon emissions that exceed oil sands industry-reported values by 1900% to over 6300%, the bulk of which was due to unaccounted-for intermediate-volatility and semivolatile organic compounds. Measured facility-wide emissions represented approximately 1% of extracted petroleum, resulting in total organic carbon emissions equivalent to that from all other sources across Canada combined. These real-world observations demonstrate total organic carbon measurements as a means of detecting unknown or underreported carbon emissions regardless of chemical features. Because reporting gaps may include hazardous, reactive, or secondary air pollutants, fully constraining the impact of anthropogenic emissions necessitates routine, comprehensive total organic carbon monitoring as an inherent check on mass closure.

Local incomplete combustion emissions define the PM2.5 oxidative potential in Northern India.

The oxidative potential (OP) of particulate matter (PM) is a major driver of PM-associated health effects. In India, the emission sources defining PM-OP, and their local/regional nature, are yet to be established. Here, to address this gap we determine the geographical origin, sources of PM, and its OP at five Indo-Gangetic Plain sites inside and outside Delhi. Our findings reveal that although uniformly high PM concentrations are recorded across the entire region, local emission sources and formation processes dominate PM pollution. Specifically, ammonium chloride, and organic aerosols (OA) from traffic exhaust, residential heating, and oxidation of unsaturated vapors from fossil fuels are the dominant PM sources inside Delhi. Ammonium sulfate and nitrate, and secondary OA from biomass burning vapors, are produced outside Delhi. Nevertheless, PM-OP is overwhelmingly driven by OA from incomplete combustion of biomass and fossil fuels, including traffic. These findings suggest that addressing local inefficient combustion processes can effectively mitigate PM health exposure in northern India.

Characterizing the sources of ambient PM10 organic aerosol in urban and rural Catalonia, Spain.

Organic aerosols (OA) have recently been shown to be the dominant contributor to the oxidative potential of airborne particulate matter in northeastern Spain. We collected PM10 filter samples every fourth day from January 2017 to March 2018 at two sampling stations located in Barcelona city and Montseny Natural Park, representing urban and rural areas, respectively. The chemical composition of PM10 was analyzed offline using a broad set of analytical instruments, including high-resolution time-of-flight mass spectrometry (HR-ToF-AMS), a total organic carbon analyzer (TCA), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), ion chromatography (IC), and thermal-optical carbon analyzer. Source apportionment analysis of the water-soluble organic content of the samples measured via HR-ToF-AMS revealed two primary and two secondary sources of OA, which included biomass-burning OA (BBOA), sulfur-containing OA (SCOA), as well as summer- and winter­oxygenated OA (SOOA and WOOA). The presence of hydrocarbon-like water-insoluble OA was also identified based on concentration trends in black carbon and nitrogen oxides. The results from the source apportionment analysis of the inorganic composition were correlated with different OA factors to assess potential source contributors. Barcelona showed significantly higher average water-soluble OA concentrations (5.63 ± 0.56 µg m-3) than Montseny (3.27 ± 0.37 µg m-3) over the sampling period. WOOA accounted for nearly 27 % of the averaged OA in Barcelona compared to only 7 % in Montseny. In contrast, SOOA had a greater contribution to OA in Montseny (47 %) than in Barcelona (24 %). SCOA and BBOA were responsible for 15-28 % of the OA at both sites. There were also seasonal variations in the relative contributions of different OA sources. Our overall results showed that local anthropogenic sources were primarily responsible for up to 70 % of ambient soluble OA in Barcelona, and regulating local-scale emissions could significantly improve air quality in urban Spain.

Ammonium-adduct chemical ionization to investigate anthropogenic oxygenated gas-phase organic compounds in urban air.

Volatile chemical products (VCPs) and other non-combustion-related sources have become important for urban air quality, and bottom-up calculations report emissions of a variety of functionalized compounds that remain understudied and uncertain in emissions estimates. Using a new instrumental configuration, we present online measurements of oxygenated organic compounds in a U.S. megacity over a 10-day wintertime sampling period, when biogenic sources and photochemistry were less active. Measurements were conducted at a rooftop observatory in upper Manhattan, New York City, USA using a Vocus chemical ionization time-of-flight mass spectrometer with ammonium (NH4 +) as the reagent ion operating at 1 Hz. The range of observations spanned volatile, intermediate-volatility, and semi-volatile organic compounds with targeted analyses of ~150 ions whose likely assignments included a range of functionalized compound classes such as glycols, glycol ethers, acetates, acids, alcohols, acrylates, esters, ethanolamines, and ketones that are found in various consumer, commercial, and industrial products. Their concentrations varied as a function of wind direction with enhancements over the highly-populated areas of the Bronx, Manhattan, and parts of New Jersey, and included abundant concentrations of acetates, acrylates, ethylene glycol, and other commonly-used oxygenated compounds. The results provide top-down constraints on wintertime emissions of these oxygenated/functionalized compounds with ratios to common anthropogenic marker compounds, and comparisons of their relative abundances to two regionally-resolved emissions inventories used in urban air quality models.

Asphalt-related emissions are a major missing nontraditional source of secondary organic aerosol precursors.

Asphalt-based materials are abundant and a major nontraditional source of reactive organic compounds in urban areas, but their emissions are essentially absent from inventories. At typical temperature and solar conditions simulating different life cycle stages (i.e., storage, paving, and use), common road and roofing asphalts produced complex mixtures of organic compounds, including hazardous pollutants. Chemically speciated emission factors using high-resolution mass spectrometry reveal considerable oxygen and reduced sulfur content and the predominance of aromatic (~30%) and intermediate/semivolatile organic compounds (~85%), which together produce high overall secondary organic aerosol (SOA) yields. Emissions rose markedly with moderate solar exposure (e.g., 300% for road asphalt) with greater SOA yields and sustained SOA production. On urban scales, annual estimates of asphalt-related SOA precursor emissions exceed those from motor vehicles and substantially increase existing estimates from noncombustion sources. Yet, their emissions and impacts will be concentrated during the hottest, sunniest periods with greater photochemical activity and SOA production.

Advances in offline approaches for trace measurements of complex organic compound mixtures via soft ionization and high-resolution tandem mass spectrometry.

Complex airborne mixtures of organic compounds can contain 10,000's of diverse compounds at trace concentrations. Here, we incorporate high-resolution mass spectrometry into our integrated offline sampling-to-analysis measurement system for routine molecular-level speciation of complex mixtures in gas- or particle-phase samples with detection limits of 2-20 pg L-1 (i.e. 0.2-1.9 ppt in 6 L samples). Analytes desorbed from custom adsorbent tubes (or filter extracts) were separated via gas chromatography (GC) and simultaneously analyzed by an electron ionization quadrupole mass spectrometer (EI-MS), and by atmospheric pressure chemical ionization (APCI) combined with a high-resolution quadrupole time-of-flight mass spectrometer (Q-TOF) with a resolution of 25,000-40,000 M/ΔM in HR-TOF and MS/MS modes. We demonstrated our system with simple standards, a Macondo crude oil standard as a reference for complex mixtures of common airborne compounds, and ambient samples using GC-TOF and GC-MS/MS. We speciated complex mixtures at mass accuracy error (i.e. mass tolerance) down to 8 ± 2 ppm (e.g. resolving analytes of mass 270.000 u with 0.003 u accuracy) using a targeted approach with 3000 molecular formulas, including hydrocarbons and functionalized analytes containing oxygen, sulfur, nitrogen, or phosphorous. This extended from compounds with 10 to 32 carbon atoms and up to 16 hydrocarbon formulas per carbon number, and a similar range for functionalized compound classes. We also demonstrated our MS/MS capabilities to differentiate structural isomers and determine the presence of specific functional groups; and our direct-TOF capability, which bypasses high-temperature chromatographic separation to preserve functionalized analytes.

Advances in offline approaches for chemically speciated measurements of trace gas-phase organic compounds via adsorbent tubes in an integrated sampling-to-analysis system.

Gas-phase organic compounds across a range of volatilities, including volatile organic compounds (VOCs), are key components of outdoor air, indoor spaces, and a variety of other anthropogenic and biogenic systems. The collection of offline samples on adsorbent-packed tubes for analysis on laboratory instrumentation has been in use for decades, but with limited sensitivities and compound coverage. We present and evaluate our integrated sampling-to-analysis system that enables offline detailed chemical characterization of multi-faceted organic mixtures at trace concentrations. Its capabilities extend across a diverse variety of VOCs with different molecular features, as well as intermediate and semivolatile organic compounds (I/SVOCs). Samples can be collected manually or via automated devices that have been applied in chamber, field, and aircraft platforms. The laboratory instrumentation can be coupled to both a high resolution mass spectrometer (MS) and a traditional quadrupole MS, though performance metrics presented in this study are determined via the traditional MS. We demonstrate capabilities for detailed chemical characterization and routine performance for a wide range of compound functionalities at sub-part per trillion (ppt) concentrations, and as low as <100 parts per quadrillion (ppq), yielding 3300 observed unique compound peaks in a single indoor air sample. These limits of detection and compound coverage were accomplished through a holistic optimization of the entire system and lifecycle of adsorbent tubes. We present our best practices for all aspects of tube production, handling, sampling, and analysis, and an examination of commercially-available materials and our custom adsorbent tubes using a diverse mix of VOC, IVOC, and SVOC standards, including difficult to measure analytes across a range of polarities and functionalities. In many aspects, the commercially-available materials and tube conditioners tested were insufficient for achieving low-ppt measurements.