Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.

The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products

Environmental screening of future gasoline additives : computational tools to estimate chemical partitioning and forecast widespread groundwater contamination

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004."September 2004."Includes bibliographical references.(cont.) application of Raoult's law for the same set of systems. An approach was developed which relates the empirical LSER solute polarity parameter, pi2Ĥ, to two more fundamental quantities: a polarizability term and a computed solvent accessible surface electrostatic term. Electrostatics computations employed dielectric field continuum models and a density functional theory (B3LYP) or efficient Hartree-Fock (HF/MIDI!) method for 90 polar and nonpolar organic solutes. Predicted pi2Ĥ values had a correlation coefficient of 0.95 and standard deviation of 0.11 relative to empirically measured values. The resulting model relies on only two fitted coefficients and has the additional advantage of potential applicability to any solute composed of C, H, N, O, S, F, C1, and Br.Fuel formulations evolve continually, and historical experience with the fuel additives tetra-ethyl lead and methyl-tert-butyl ether (MTBE) indicates that newly proposed additives should be screened for their potential to threaten environmental resources, before they are used widely. A physical-chemical transport model was developed to forecast well water concentrations and transport times for gasoline components migrating from underground fuel tank releases to vulnerable community water supply wells. Transport calculations were parameterized using stochastic estimates of representative fuel release volumes and hydrogeologic characteristics, and were tailored to individual compounds based on their abundances in gasoline, gasoline-water partition coefficients, and organic matter-water partition coefficients. With no calibration, the screening model successfully captured the reported magnitude of MTBE contamination of at-risk community supply wells. To estimate gasoline-water partition coefficients for unstudied solutes, we combined linear solvation energy relationships (LSERs) developed for pure 1:1 systems using linear solvent strength theory and a "solvent compartment" model. In this way, existing LSERs could be extended to treat solute partitioning from gasoline, diesel fuel, and similar mixtures into contacting aqueous mixtures. This allowed prediction of liquid-liquid partition coefficients in a variety of fuel-water systems for a broad range of dilute solutes. When applied to 37 polar and nonpolar solutes partitioning between an aqueous mixture and 12 different fuel-like mixtures (many including oxygenates), the estimated model error was a less than a factor of 2 in the partition coefficient. This was considerably more accurate thanby J. Samuel Arey.Ph.D

Anticipation nationwide risks to drinking water : predicting local scale contamination of community supply wells by gasoline additives

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001."June 2001."Includes bibliographical references.Only ten years after the increased addition of methyl-tert-butyl-ether (MTBE) to U.S. gasolines, nationwide MTBE contamination of thousands of drinking water supply wells has been widely documented, reflecting enormous environmental and economic costs. Due to its abundance in gasoline, high aqueous solubility, and slow degradation rate in aquifers, MTBE has migrated in significant quantities from subsurface gasoline spills to a substantial number of community and private drinking water wells in a short period of time. For the purposes of this project, it was hypothesized that the tendency for gasoline additives to contaminate subsurface drinking water resources could be accurately predicted a priori using a generalized transport model. A screening method was developed to predict both the migration times of gasoline constituents from a leaking underground fuel tank (LUFF) to a community drinking water supply well and expected contaminant levels in the well. A review of literature revealed that U.S. municipal drinking water supplies are typically found in shallow sand and gravel aquifers. A subsurface transport model was parameterized based on the proximity of community supply wells to LUFTs (1000 in); probable characteristics of sand and gravel aquifers; typical pumping rates of community supply wells (80 to 400 gal/min); and reasonable gasoline spill volumes from LUFTs (100 to 1000 gal). The transport model was tailored to individual solutes based on their estimated abundances in gasoline, gasoline-water partition coefficients (Kgw), and estimated organic matter-water partition coefficients (Kom). Transport calculations were conducted for 17 polar and four nonpolar compounds currently proposed for or found in contemporary U.S. gasolines, including MTBE, ethanol, and methanol. Subsurface degradation processes were not considered. The transport model predicted MTBE concentrations of 40 to 500 ppb in municipal wells, which compared favorably with observed well concentrations at a significant proportion of sites in the U.S. The transport model therefore captured the order of magnitude of observed MTBE contamination of municipal wells without any use of adjustable or "fitted" parameters. Subsurface transport calculations of gasoline constituents required prior knowledge or estimation of their gasoline-water partition coefficient and organic matterwater partition coefficients. In anticipation of the need to conduct transport calculations for novel or previously unstudied compounds, a review of methods for calculating or predicting solute partition coefficients in gasoline-water, organic matter-water, and octanol-water systems was conducted. Additionally, a new linear solvation energy relationship (LSER) was developed for estimating gasoline-water partition coefficients of organic compounds, having an estimated standard error of 0.22 log Kgw units.by J. Samuel Arey.S.M

Laboratory Studies of Processing of Carbonaceous Aerosols by Atmospheric Oxidants/Hygroscopicity and CCN Activity of Secondary & Processed Primary Organic Aerosols

The atmosphere is composed of a complex mixture of gases and suspended microscopic aerosol particles. The ability of these particles to take up water (hygroscopicity) and to act as nuclei for cloud droplet formation significantly impacts aerosol light scattering and absorption, and cloud formation, thereby influencing air quality, visibility, and climate in important ways. A substantial, yet poorly characterized component of the atmospheric aerosol is organic matter. Its major sources are direct emissions from combustion processes, which are referred to as primary organic aerosol (POA), or in situ processes in which volatile organic compounds (VOCs) are oxidized in the atmosphere to low volatility reaction products that subsequent condense to form particles that are referred to as secondary organic aerosol (SOA). POA and VOCs are emitted to the atmosphere from both anthropogenic and natural (biogenic) sources. The overall goal of this experimental research project was to conduct laboratory studies under simulated atmospheric conditions to investigate the effects of the chemical composition of organic aerosol particles on their hygroscopicity and cloud condensation nucleation (CCN) activity, in order to develop quantitative relationships that could be used to more accurately incorporate aerosol-cloud interactions into regional and global atmospheric models. More specifically, the project aimed to determine the products, mechanisms, and rates of chemical reactions involved in the processing of organic aerosol particles by atmospheric oxidants and to investigate the relationships between the chemical composition of organic particles (as represented by molecule sizes and the specific functional groups that are present) and the hygroscopicity and CCN activity of oxidized POA and SOA formed from the oxidation of the major classes of anthropogenic and biogenic VOCs that are emitted to the atmosphere, as well as model hydrocarbons. The general approach for this project was to carry out reactions of representative anthropogenic and biogenic VOCs and organic particles with ozone (O3), and hydroxyl (OH), nitrate (NO3), and chlorine (Cl) radicals, which are the major atmospheric oxidants, under simulated atmospheric conditions in large-volume environmental chambers. A combination of on-line and off-line analytical techniques were used to monitor the chemical and physical properties of the particles including their hygroscopicity and CCN activity. The results of the studies were used to (1) improve scientific understanding of the relationships between the chemical composition of organic particles and their hygroscopicity and CCN activity, (2) develop an improved molecular level theoretical framework for describing these relationships, and (3) establish a large database that is being used to develop parameterizations relating organic aerosol chemical properties and SOA sources to particle hygroscopicity and CCN activity for use in regional and global atmospheric air quality and climate models

Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City

Understanding sources, concentrations, and transformations of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere is important because of their potent mutagenicity and carcinogenicity. The measurement of particle-bound PAHs by three different methods during the Mexico City Metropolitan Area field campaign in April 2003 presents a unique opportunity for characterization of these compounds and intercomparison of the methods. The three methods are (1) collection and analysis of bulk samples for time-integrated gas- and particle-phase speciation by gas chromatography/mass spectrometry; (2) aerosol photoionization for fast detection of PAHs on particles' surfaces; and (3) aerosol mass spectrometry for fast analysis of size and chemical composition. This research represents the first time aerosol mass spectrometry has been used to measure ambient PAH concentrations and the first time that fast, real-time methods have been used to quantify PAHs alongside traditional filter-based measurements in an extended field campaign. Speciated PAH measurements suggest that motor vehicles and garbage and wood burning are important sources in Mexico City. The diurnal concentration patterns captured by aerosol photoionization and aerosol mass spectrometry are generally consistent. Ambient concentrations of particle-phase PAHs typically peak at ~110 ng m^-3 during the morning rush hour and rapidly decay due to changes in source activity patterns and dilution as the boundary layer rises, although surface-bound PAH concentrations decay faster. The more rapid decrease in surface versus bulk PAH concentrations during the late morning suggests that freshly emitted combustion-related particles are quickly coated by secondary aerosol material in Mexico City's atmosphere and may also be transformed by heterogeneous reactions

Floating oil-covered debris from Deepwater Horizon : identification and application

Author Posting. © IOP Publishing, 2012. This article is posted here by permission of IOP Publishing. Re-use is limited to non-commercial purposes. The definitive version was published in Environmental Research Letters 7 (2012): 015301, doi:10.1088/1748-9326/7/1/015301.The discovery of oiled and non-oiled honeycomb material in the Gulf of Mexico surface waters and along coastal beaches shortly after the explosion of Deepwater Horizon sparked debate about its origin and the oil covering it. We show that the unknown pieces of oiled and non-oiled honeycomb material collected in the Gulf of Mexico were pieces of the riser pipe buoyancy module of Deepwater Horizon. Biomarker ratios confirmed that the oil had originated from the Macondo oil well and had undergone significant weathering. Using the National Oceanic and Atmospheric Administration's records of the oil spill trajectory at the sea surface, we show that the honeycomb material preceded the front edge of the uncertainty of the oil slick trajectory by several kilometers. We conclude that the observation of debris fields deriving from damaged marine materials may be incorporated into emergency response efforts and forecasting of coastal impacts during future offshore oil spills, and ground truthing predicative models.This research was supported by NSF grant OCE-1043976 to CR