Chemical and biological implications of organic compounds formed in simulated and real urban atmospheres

Abstract

The U.S. Clean Air Act, as amended in August, 1977, requires the U.S. Environmental Protection Agency to evaluate the health effects, atmospheric sources, transformations, and sinks of a variety of nitrogenous compounds and polycyclic aromatic hydrocarbons (PAH). Results from our recent research on real and simulated urban atmospheres pertinent to both classes of compounds are summarized here. The reactions in air of ∼500 parts/10 9 (ppb) of diethyl- or triethylamine (DEA or TEA) with 10 to 20 ppb of NO and NO 2 and traces of HONO were studied in a 50-m 3 outdoor chamber. Product analysis was by gas chromatography-mass spectrometry (gc-ms). Diethylnitrosamine [(C 2H 5) 2NNO, DEN] was readily formed in the dark from DEA (∼3% yield) but was destroyed in sunlight. Traces of DEN were also formed from TEA in the dark, but in sunlight its yield increased to a maximum of ∼2%. Other photo-oxidation products from both amines included large amounts of diethylnitramine [(C 2H 5) 2NNO 2], substituted amides, and those pollutants characteristic of photochemical smog [e.g., O 3, peroxyacetylnitrate (PAN), and light-scattering aerosols]. Both (C 2H 5) 2NNO and acetamide (found in the aerosol phase) are known carcinogens in animals. Dimethylnitramine is also a carcinogen and was identified as a major product in exploratory dimethylamine-NO x -air runs. Similar studies of possible carcinogenic activity do not appear to have been conducted with (C 2H 5) 2NNO 2 and the substituted amides. In another type of experiment, such nitrogenous species as N 2O 5, HNO 3, HONO, PAN, CH 3ONO 2, and peroxynitric acid (HO 2NO 2), as well as HCOOH and H 2CO were identified by long-path (85-m) high-resolution Fourier transform infrared spectroscopy (FT-IR) when a propylene-NO x -air mixture was irradiated at 10°C in our 5500-liter evacuable chamber with a 24-kW solar simulator. With a second FT-IR spectrometer (optical pathlength, 1.08 km) employed in an outdoor environmental chamber, ppb levels of HNO 3, NH 3, HCOOH and H 2CO were identified in “aged” ambient photochemical smog. The Ames Salmonella typhimurium assay has been applied to the organic extracts of ambient particulates collected at 11 urban sites throughout the Los Angeles basin. The extracts all showed frameshift-type mutagenic activity without metabolic activation. Thus, in addition to benzo( a)pyrene (which requires S-9 activation in the Ames test), other mutagenic compounds must be present—possibly BaP or other PAH activated by chemical reactions with compounds present in smog, including NO 2 and O 3. We propose that such reactions may take place not only in the atmosphere, but also possibly on the filter itself during sample collection; studies are under way to determine the magnitude of such possible filter artifacts.