Environ. Sci. Technol. 2003, 37, 16-21
Alkyl Amides and Nitriles as Novel Tracers for Biomass Burning B E R N D R . T . S I M O N E I T , * ,† A. I. RUSHDI,† M. R. BIN ABAS,‡ AND B. M. DIDYK§ Environmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, Department of Chemistry, Universiti Malaya, Kuala Lumpur, Malaysia, and Refineria de Petroleo, Concon, Chile
The occurrence of n-alkanoic acids, amides, and nitriles in samples of aerosol particulate matter from Kuala Lumpur and Santiago suggests that emissions from cooking and biomass burning are the primary sources of these organic markers in the atmosphere. It is proposed that fatty acids react with ammonia during biomass burning or combustion to produce amides and nitriles, which can be applied as useful biomarker tracers. To test this hypothesis, nonadecanoic acid and hexadecanamide were used as reactants in hydrous pyrolysis experiments. These experiments produced amides and nitriles and indicated that ammonia is an essential agent in their formation. Thus amides and nitriles are of utility as indicators for input from combustion and biomass burning in the ambient atmosphere.
Introduction Biomass burning has been recognized as a major contributor to the global particle burden in the atmosphere (e.g., refs 1-6). Its emissions can also overwhelm the other carbonaceous aerosol particles in urban areas (e.g., refs 6-8). Biomass combustion is an additional important primary source of many trace substances that are reactants in atmospheric chemistry and of carbonaceous soot (charcoal) particulate matter which decreases visibility and absorbs incident radiation (e.g., refs 1-3, 6, 9). It is an incomplete combustion process, analogous to laboratory hydrous pyrolysis, and thus emits organic compound tracers in the smoke particulate matter (6). However, the organic compound compositions of biomass burning emissions are just beginning to be reported from primary sources (10-27) and are being incorporated into models of the receptor ambient atmosphere (e.g., refs 7 and 8). Various markers for biomass burning input have been utilized (e.g., potassium, retene, numerous resin terpenoids, steroids, levoglucosan, etc.), but there are always exceptions and new unknown compounds in emissions (6). For example, potassium is not a unique tracer for wood smoke because it has other emission sources such as grilling/ frying in food preparation (28, 29) and retene (30) is not always emitted at detectable concentrations from burning conifer wood, whereas the resin acids are, especially dehydroabietic acid (25, 27). A related input of biogenic organic compounds from cooking in food preparation (grilling/frying, etc.), from rendering and crematorium facilities, from open * Corresponding author fax: (541)737-2064; e-mail: simoneit@coas. oregonstate.edu. † Oregon State University. ‡ Universiti Malaya. § Refineria de Petroleo. 16
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 1, 2003
FIGURE 1. GC-MS data for alkanones and alkyl nitriles in an aerosol sample from Kuala Lumpur, Malaysia during a haze episode in September 1991 (31): (a) m/z 58 + 59, key ion for n-alkan-2-ones and (b) total ion current trace of the ketone fraction (F3). Numbers indicate carbon chain length, dots are alkanones. garbage burning (urban refuse), etc. should also be considered in the overall biomass combustion process (5, 6). Some of the same organic tracer compounds are found in these emissions as in smoke from natural biomass fires (e.g., levoglucosan (23)). Thus, there is a continued need to define and validate additional specific tracers for biomass burning emissions. Here we report on a series of chemical transformations of fatty acids reacting with ammonia during biomass burning, both in wildfires and in urban areas from food preparation and related anthropogenic activities, to produce complementary tracers as amides and nitriles.
Experimental Methods Samples and Extraction. Aerosol samples were acquired by high volume filtration for TSP or with size cut
