Environ. Sci. Technol. 1998, 32, 577-583
Azaarenes in the Aerosol of an Urban Atmosphere HUNG-YU CHEN† AND MARTIN R. PRESTON* Oceanography Laboratories, Earth Sciences Department, University of Liverpool, Liverpool, L69 3BX, U.K.
The results of an extensive study of 47 azaarenes in the Liverpool urban atmosphere through the period from September 1994 to March 1996 are reported. Total suspended particles and size-fractionated particles were collected by high volume sampling techniques and cascade impactor sampling techniques. The overall mean ∑azaarene concentration was 2.80 ng m-3. The monthly mean ∑azaarene concentrations show a very strong seasonal variation in which the maximum concentration occurred in the winter and the minimum in the summer months, with a concentration range of 0.4-7.64 ng m-3. There are highly significant covariations between the different ring sized group, which suggests that there are similar source strengths and transport mechanisms for these compounds. The particle size distributions indicate that the combustion of fossil fuel is probably the main source of azaarene compounds during the winter. The percentage concentrations of azaarene show that these compounds also tend to associate with larger particles in warm periods and enrich in fine particles in cold weather conditions.
Introduction Azaarene compounds are N-heterocycles, composed of both an aromatic and a six-membered ring structure, in which a carbon is replaced by nitrogen (1). Like their parent compounds, polycyclic aromatic hydrocarbons (PAHs), azaarenes are also the products of combustion processes, but azaarenes are more soluble in water than PAHs (2). Fossil fuels are the major sources of polycyclic aromatic compounds (PACs). For example, coal contains a variety of heterocyclic nitrogen compounds, and through the extensive use of fossil fuels, including coal, azaarenes have become widespread in the environment (3-5). PACs which are emitted into the atmosphere in the vapor phase PACs may become sorbed onto the surface of the soot particles, which are also formed under the same condition as PAC compounds. Because smaller particles have greater surface areato-volume ratios, PAC compounds become preferentially associated with them. In the U.K., vehicle emissions probably contribute the major portion of PACs in nonwinter period, but house heating or power station production is the most important in winter (6). Wild and Jones (7) also reported that domestic coal combustion was thought to be the primary source of PAHs to the atmosphere (84% of total emissions) in the U.K. Many studies have shown that the proportion of PAHs associated with small particles decreases in warmer weather * To whom correspondence should be addressed. Fax: (+)44 (0) 151-794-4099; e-mail:
[email protected]. † Present address: Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei, Taiwan. S0013-936X(97)00033-3 CCC: $15.00 Published on Web 01/22/1998
1998 American Chemical Society
conditions (8, 9). Gardner et al. (6) suggested that the PAH concentration in the fraction 1.1 µm decreases from summer through spring/autumn to winter in the U.K. This may have resulted from a different particle size distribution characteristics of the large amounts of combustion products of fossil fuels which have been emitted to the atmosphere by power station or house heating during the winter. This would also explain a strong seasonal variation in U.K. samples (and elsewhere). Like other PACs, some members of azaarenes are known as mutagens and/or carcinogens (10). Two- and three-ring azaarenes have broad reactivity in vivo, with threshold effects observed in membrane structure-function and respiratory process (11). Many studies have indicated that some of azaarenes, including quinoline, 4- and 8-methylquinoline, acridine, and benzoquinolines, are active as tumor initiators on mouse skin (12). Some nitrogen-containing PACs are also phytotoxic (13). Azaarenes have been found in a number of environmental media, including urban aerosols (14-17), marine and freshwater sediments (18-20), and crude oil and petroleum products (21, 22). However, much less is known about the atmospheric levels and reactions of azaarenes than for their parent PAHs; these areas warrant further research. So far, the transport mechanisms of azaarenes in the atmosphere still have not been well studied, and the present work represents part of an ongoing programmed of investigation of contaminant inputs to marine systems from the atmosphere.
Experimental Section Sample Collection. The sampling site was located on the roof of a building at the University of Liverpool close to Liverpool City center. The building is about 25 m tall from ground level and 40 m away from the main road. At the same sampling site, there was also a meteorological station supplying temperature, wind speed, and direction and rainfall data. A high volume air sampling system (hi-vol) (GMWS-2310 ACCU-VOL; General Metal Works Inc., OH) was utilized to collect particulate aerosols in this study. The standard glass fiber filters (203 × 254 mm) were used for total particle sampling and as the backup filter for the cascade impactor (CI). The filters have a reported collection efficiency of 99.998% for 0.3-0.4 µm particles. The slotted CI glass fiber filters (146 × 153 mm) which have equivalent cutoff diameters at 50% efficiency were used for size fractionated particle collection. At intervals, a cascade impactor was substituted for the high volume filter hold so as to sample the different sizes of azaarene aerosol. In this paper, the size distributions are as follows (23, 24): stage 1 (>9.3 µm), stage 2 (3.9-9.3 µm), stage 3 (1.97-3.9 µm), stage 4 (1.28-1.97 µm), stage 5 (0.67-1.28 µm), and stage 6 (0.67-0.40 µm). Any particles passing completely through the CI are trapped on a final backup filter ( spring > summer. In the winter of 1994/1995, the distributions of total concentrations on the different stages of the CI-1 sample increased with the decreasing particle size, with over 85% of the azaarenes associated with particles of size less than 0.67 mm. In Antwerp (Belgium) urban aerosols also showed the same distribution pattern (30) in which about 85.4% of PAHs were associated with particles of sizes 0.67 ) ∑(stages 1-5)] show a consistent increased trend following the seasonal variations (winter < spring < summer; Figure 4a). The total percentage concentrations for ∑P>0.67 on these four CI samples are 11.1, 19.3, 24.9, and 38.1% for the samples of January, April, July, and August 1995, respectively. However, for particle sizes smaller than 0.67 µm (∑P1.28 are 9.6, 20.8, 31.9, and 20.1% for the sample of January, April, July, and August 1995, respectively. Like 2- and 3-ring species, the percentage concentrations of 4-ring azaarenes also decrease with the seasonal change (winter > spring > summer) for the particles smaller than 1.28 mm [∑P
