Final Report: Transformations of Selected Organic Urban HAPs: Mechanistic and Modeling Studies to Identify Cancer and Non-Cancer Human Health RiskEPA Grant Number: R826247
Title: Transformations of Selected Organic Urban HAPs: Mechanistic and Modeling Studies to Identify Cancer and Non-Cancer Human Health Risk
Investigators: Jeffries, Harvey E.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Chung, Serena
Project Period: December 8, 1997 through December 7, 2000
Project Amount: $540,000
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
The main objectives of this research project are to: (1) advance fundamental knowledge of atmospheric transformation of organic hazardous air pollutants (HAPs)-initially, 1,3-butadienes, aromatics, and epoxides were studied, and in subsequent years, this was expanded to other HAPs; (2) include the large variety of organic HAPs in modern air quality models by extensions of the newly developed "morphecules" concept; and (3) design and prepare a HAPs mixture for testing HAPs behavior in an urban-like environment, and for evaluating the allomorphic/morphecule representation and other mechanisms for air quality models.
Smog-chamber experiments were conducted with dialkenes (1,3-butadienes) and major transformation products (such as acroleins and organic acids), with analytical measurements, including those with techniques developed for this project. This will lead to advances in the understanding of the chemistry of these compounds and improvements in chemical mechanisms used to simulate the atmospheric transformations and fate of these compounds. Smog-chamber experiments also were conducted with 1,4-unsaturated dicarbonyls, known to be products of aromatic photochemical oxidation and transformation products of major importance, with analytical measurements including those with techniques developed for this project. This will lead to advances in the understanding of the chemistry of these compounds and improvements in chemical mechanisms used to simulate the atmospheric transformations and fate of these compounds. HAPs emissions data were obtained from several sources, and HAPs mixtures have been designed for smog-chamber tests. Smog-chamber tests also were conducted with the HAPs mixtures, and chemical analysis by gas chromatography (GC) and mass spectrometry (MS) show many products from transformation of key HAPs and HAPs mixtures. Mechanism development and modeling studies also were conducted with new and previous experiments.
Design of HAPs Mixtures: Types of Mixtures and Composition Tables. Several sources of information, which can be used to determine the relative composition of ambient toxic chemicals, were consulted. These include reports published by, and accessible from, the U.S. Environmental Protection Agency (EPA) (see Relevant Web Sites), including the Toxic Release Inventory (TRI), the EPA Integrated Urban Toxics Project (EPA HAPs List), and the National Vehicle Toxics Emissions project. The resulting mixtures designed and used for smog-chamber tests are shown in a table on the University of Northern California (UNC) Web Site (see Relevant Web Sites). Although the composition is based on data from published reports, the exact composition of the mixtures is not critical as long as it is known and can be specified in simulation models and resulting yields of products can be determined relative to the starting parent compounds. The objective was to conduct experiments with known major HAPs, in chamber experiments. The first few of these were not too complex, and they reflect relative contributions based on mass or toxicity found in the atmosphere. Most of the HAPs are constituents of the SynUrban mixture, which is based on the EPA's national ambient volatile organic compound (VOC) measurements also used to conduct experiments for this project. In addition, individual aldehyde HAPs were compared directly with the SynUrban mixture for two reasons: (1) to check the light assumptions used to model these experiments; and (2) to study some important HAPs, which never have been studied individually before.
Chamber Experimental Results Using HAPs Mixtures, Including Decay Rates and Transformation to Other Products: Smog-Chamber Experiments. Tables on the UNC Web Site list the chamber experiments conducted during this last year, including both those using individual HAPs and the HAPs mixtures. These are daytime experiments starting at sunrise, lasting for about 10 hours, and nighttime experiments to study chemistry without photolytic processes. Each experiment's results are in a file containing documentation and physical- and time-concentration data. Each experiment listed in the tables is linked to a plot of the time-concentration data for NOx and O3, and basic physical data of sunlight, temperature, and dewpoint. The smog-chamber facilities are described in another linked and downloadable document. Analysis of GC and MS of chemical products formed during the chamber experiments' photochemically induced transformations of the parent HAPs are presented. Photooxidation or decay rates of the parent HAPs are compared relatively to the more studied HAPs, as well as absolutely, to known OH rates as a way to determine the presence of other significant chemistry.
Mechanism Development and Modeling Studies of Previous Experiments. Modeling efforts to date have focused on individual HAPs such as the dienes and their major products, and the aromatic 1,4-unsaturated dicarbonyl products. Progress and success is mixed. As an example, the simulations are good in reproducing the experimental observations for the parent hydrocarbons in the case of dienes and their primary products such as methacrolein, but the simulations of the organic acids are underpredicting the observations (in which we have high confidence). Progress has been made in the testing and further development of the chemistry of the 1,4 unsaturated dicarbonyl products, and it is clear that more experimental work is needed.
Research Needs Identified, and Recommendations for Future Work. This report shows that smog chambers can be used to conduct experiments in a realistic and controlled method, which can allow measurements and provide data. These data can be used to increase our understanding of important atmospheric processes of the fate and transformation of HAPs, and improve chemical mechanisms, which can be used in air quality simulation models. First-time measurements of products from the transformation of HAPs or other atmospheric pollutants were made including quantification of yields and time-series allowing for testing of chemical models. An important observation and conclusion is that most organic HAPs and most other organic compounds involved in atmospheric chemistry are transformed to some degree to products containing oxygen, often in the form of carbonyls, with the most widespread example being formaldehyde. Formaldehyde is one of the EPA HAPs that is of major concern. This has important consequences for regulators attempting to prioritize and control HAPS-compounds that are considered less harmful, but may be emitted in large amounts, such as methanol, should be treated as a major source of formaldehyde through atmospheric transformation chemistry. Improvements in the chemical mechanisms have been demonstrated by computer simulation of the experiments. Significant findings were published in major peer-reviewed scientific journals and were the subject of many presentations.
This project also shows how much effort is needed to study a few important compounds in several classes of HAPs. This effort can and should be continued with many of the remaining HAPs on the EPA's list. This effort can be assisted greatly by simultaneous support of the synthesis of proposed product compounds for verification of identification, quantification of yields, and conducting additional experiments of these compounds to directly determine the fate of not only these products, but of the original HAPs of interest. To allow for the detection of more products, measurements from experiments with more complex atmospheric mixtures, and experiments conducted at lower concentrations, the use and development or purchase of more sensitive analytical instruments to support these experiments should be funded. Another type of project, which might greatly assist in the type of research presented in this report, would be the separation and fractional collection by preparative high-performance liquid chromatography (HPLC) methods of the output from continuously operated flow-reactor experiments similar in composition to the experiments presented in this report. This would provide useful quantities of the products, which would eliminate the need to fund the synthesis of tentatively identified products, and allow for not only atmospheric experiments, but also for toxicological screening procedures.
Computer simulations of some of the experiments conducted for this project have shown that the current state of knowledge is fairly good for simulating the primary oxidation of the parent HAPs and the formation of several major products and incomplete and unsuccessful for other major products.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 13 publications||1 publications in selected types||All 1 journal articles|
||Liu X, Jeffries HE, Sexton KG. Atmospheric photochemical degradation of 1,4-unsaturated dicarbonyls. Environmental Science & Technology 1999;33(23):4212-4220.||