Alkyl Amides and Nitriles as Novel Tracers for Biomass Burning BERND R. T. SIMONEIT,* ,† A. I. RUSHDI, † M. R. BIN ABAS, ‡ AND B. M. DIDYK § Environm ental and Petroleum Geochem istry Group, College of Oceanic and Atm ospheric Sciences, Oregon State University, Corvallis, Oregon 97331, Departm ent of Chem istry, 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 Biomassburninghasbeen recognized asa majorcontributor to the global particle burden in the atmosphere (e.g., refs 1-6). Its emissions can also overwhelm the other carbon- aceous aerosol particles in urban areas (e.g., refs 6-8). Bio- mass combustion is an additionalimportant primarysource of many trace substances that are reactants in atmospheric chemistry and of carbonaceous soot (charcoal) particulate matter which decreasesvisibilityand absorbsincident radia- tion (e.g., refs 1-3, 6, 9).It is an incomplete combustion pro- cess, 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 re- ported from primary sources (10-27) and are being incor- porated 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 emis- sions (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 dehy- droabietic acid (25, 27). Arelated input of biogenic organic compounds from cookingin food preparation (grilling/frying, etc.), from rendering and crematorium facilities, from open 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 emis- sions as in smoke from natural biomass fires (e.g., levoglu- cosan (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 offattyacidsreactingwith ammonia duringbiomassburning, both in wildfires and in urban areas from food preparation and related anthropogenic activities, to produce comple- mentary tracers as amides and nitriles. Experimental Methods Samples and Extraction. Aerosol samples were acquired by high volume filtration for TSP or with size cut <10 µm (PM- 10) at various stations in Kuala Lumpur, Malaysia in 1991, and in Santiago, Chile in 1991, 1997, 1998, and 1999 ((31, 32) and Didyk et al., 2000, unpublished data). The samples were acquired on precleaned glass fiber or quartz fiber filters which were stored in precleaned glass jars after samplingin a freezer until analysis. The flow rate of the sampler was typically 1.4 m 3 /min and sampling durations were for 24 h. The filters were extracted twice with 400 mL of redistilled dichlo- romethane and methanolmixture (3:1)usingultrasonication for 15min each.The extracts were decanted and concentrated on a Bu ¨chi rotary evaporator (bath temperature e30 °C) to approximately 5 mL and then filtered through a Gelman- Swinneyfiltration unit fitted with precleaned glass fiber filters to remove quartz fibers and particulate detritus. Aliquots of extracts were concentrated further by nitrogen blow-down prior to instrumental analysis. Hydrous Pyrolysis . Stainless steel vessels (316SS Sno- Trik high-pressure couplings (33)) with internal capacities of286 ( 0.02 µLwere used to generate the alteration products of n -nonadecanoic acid and palmitamide with ammonium bicarbonate underhydrouspyrolysisconditions.The vessels are capable ofhandlingsystem pressure to 60 000psi(413 000 kPa). Two sets of reaction conditions were used for each compound.The first consisted ofa mixture ofdoublydistilled water (DDW) (Burdick and Jackson) with the acid or amide plus (NH4)HCO3 (hydrous pyrolysis), and filling the vessels to capacity prior to sealing, thus leaving no headspace. The second series were the same mixtures as the first with the addition of pre-extracted oxalic acid (99.5%, EM Science) to induce reductive hydrous pyrolysis conditions. Only DDW was added in the case of palmitamide. *Corresponding author fax: (541)737-2064; e-mail: simoneit@coas. oregonstate.edu. † Oregon State University. ‡ Universiti Malaya. § Refineria de Petroleo. FIGURE1. GC-M S 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. Environ. Sci. Technol. 2003, 37, 16-21 16 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 1, 2003 10.1021/es020811y CCC: $25.00  2003 American Chemical Society Published on Web 11/23/2002