Environ. Sci. Technol. 2005, 39, 7430-7438
Molecular Characteristics of Urban Organic Aerosols from Nanjing: A Case Study of A Mega-City in China G E H U I W A N G †,‡ A N D K I M I T A K A K A W A M U R A * ,† Institute of Low Temperature Science, Hokkaido University, Kita 19, Nishi 8, Kita-ku, Sapporo 060-0819, Japan, and School of the Environment, State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093, China
Over 90 organic species have been determined in fine aerosols (PM2.5) collected during the summer and winter in Nanjing, a typical mega-city in China, using gas chromatography-mass spectrometry. The organic compounds detected were apportioned to four emission sources (i.e., plant emission, fossil fuel combustion, biomass burning, and soil resuspension) and secondary oxidation products. The most abundant classes of compounds are fatty acids, followed by sugars, dicarboxylic acids excluding oxalic and malonic acids, and n-alkanes, while alcohols, polyols/polyacids and lignin/sterols are less abundant. Total amounts of the seven classes of compounds were on average 938 ng m-3 in the summer and 1301 ng m-3 in the winter, respectively, contributing 0.26-1.96% of particle mass (PM2.5). In the summer, n-alkanes were heavily enhanced by vegetation emissions with a maximum carbon number (Cmax) at C29, whereas they were dominated by emissions from fossil fuels combustion with a Cmax at C22/ C23 in the winter. Concentrations of unsaturated fatty acids were lower in the summer than in the winter, being consistent with enhanced photooxidation of unsaturated fatty acids in the summer. Concentrations of dicarboxylic acids for the summer aerosols were much higher in the daytime than in the nighttime, indicating increased photochemical production in the daytime. In the summer, plant emissions were the most significant source of organic aerosols, contributing more than 33% of total compound mass (TCM), followed by fossil fuel combustion or secondary oxidation. In contrast, fossil fuel combustion was the dominant source of winter organic aerosols, contributing more than 51% of TCM, followed by plant emissions and secondary oxidation products. The quantitative results on sugars and lignin pyrolysis products further suggested that biomass burning and soil resuspension are also significant sources of urban organic aerosols.
Introduction Atmospheric aerosols have received much attention for the past decade due to their relevance for radiative forcing of climate change and pollution transport (1-4). Atmospheric * Corresponding author phone: 81-11-706-5457; fax: 81-11-7067142; e-mail:
[email protected]. † Hokkaido University. ‡ Nanjing University. 7430
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 19, 2005
pollution in China, especially in Chinese mega-cities, is an increasingly severe problem due to its rapid industrialization and urbanization. There has been a tendency for increased summer floods in south China and enhanced drought in north China (5). Such changes may be potentially attributed to man-made light-absorbing aerosols emitted from remote populous industrial regions that alter the regional atmospheric circulation. Dust plumes from north China, containing toxic contaminants, can cause public health problems in China, Japan, Korea, and the United States (6). The emissions of aerosols and their precursors from East Asia, especially China, have been recognized to have an impact on regional and global changes in the atmospheric composition (7). A number of investigations have been conducted to characterize inorganic components of aerosols from China, because the deserts of western China are known to be a significant source of dust (8-11). However, studies on organic aerosols of Chinese mega-cities are limited on a molecular level. Only a few studies reported the organic chemical composition of Chinese urban aerosols (12-14), presenting a limited number of organic compound classes. Air pollution has been a persistent problem in Nanjing, a typical mega-city located in east China with a population of over 4 million and several huge industrial regions. Previous studies showed that the concentration of atmospheric particles with an aerodynamic diameter less than 2.5 µm was about 2-4 times more abundant than the U. S. EPA regulations (15, 16). To understand the organic composition characteristics of atmospheric aerosols of the mega-city, aerosol sampling was conducted on a day/night basis in the Nanjing urban area during the summer (July 2004) and the winter (January 2005). Here, we report on organic compositions in the aerosols including polar (i.e., saccharides, dicarboxylic acids, fatty alcohols, fatty acids, polyols/polyacids, and lignins/sterols) and nonpolar (i.e., normal alkanes) compounds using gas chromatography-mass spectrometry (GC-MS). Their molecular characteristics, diurnal variations, seasonal differences, and potential sources are also discussed. To our best knowledge, this is one of the most comprehensive data sets on various polar compounds in aerosols from Chinese mega-cities. Our work adds to the increasing chemical database on Chinese aerosols and would be helpful for scientists to fully understand the role of Chinese aerosols in global climate changes and pollution transport.
Experimental Section Aerosol Sampling. A day- and nighttime sampling was carried out on the campus of Nanjing University located in a typical urban site of a Chinese mega-city during a week in July 2004 and January 2005 to better understand summer and winter aerosol properties. Daytime sampling was conducted from 8:00 a.m. to 6:30 p.m. while nighttime sampling was conducted from 7:00 p.m. to 7:30 a.m. Aerosol samples (PM2.5) (n ) 28) were collected on precombusted (500 °C, 4 h) glass fiber filters (20 × 25 cm2) using an Andersen PM2.5 sampler (Anderson Instruments, Smyrna, GA) with a flow rate of 1.11 m3 min-1. The sampler was set up on the rooftop of a twofloor building on the campus, about 8 m above the ground. Two field blank filters were collected during the sampling period. All of the filters were equilibrated in a desiccator for 24 h before and after the aerosol sampling and then weighed to determine aerosol mass. After being weighed, the filter was placed into a clean glass jar with a Teflon-lined cap and stored at -20 °C prior to analysis. Average values of ambient temperature and visibility during the sampling period are shown in Table 1. The lower temperature and the lower 10.1021/es051055+ CCC: $30.25
2005 American Chemical Society Published on Web 09/01/2005
TABLE 1. Meteorological Conditions during the Sampling Perioda summer (July 1-7, 2004) daytime nighttime average temperature (°C) average visibility (km) a
31.7 6
28.4 3.1
winter (January 7-13, 2005) daytime
nighttime
4.7 4.6
1.5 2.8
Data from http://www.wunderground.com.
visibility suggested the development of inversion layers in the nighttime, especially on the winter nights. Extraction and Derivatization. A filter aliquot (approximately 30 cm2) was cut into pieces and sonicated three times for 10 min each with dichloromethane/methanol (2:1, v/v). The solvent extracts were filtered through quartz fiber wool packed in a Pasteur pipet, concentrated by the use of a rotary evaporator, and then blown down to dryness with pure nitrogen gas. The extracts were converted to trimethylsilyl derivatives by reaction with 50 µL of N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylsilyl chloride and 10 µL of pyridine at 70 °C for 3 h. This procedure derivatizes COOH and OH groups to the corresponding trimethylsilyl (TMS) esters and ethers, respectively (17-19). After reaction, the derivatives were diluted by the use of 140 µL of hexane with 1.43 ng µL-1 of the internal standard (nalkane C13). The field and laboratory blanks were treated as the real samples for quality assurance. Gas Chromatography-Mass Spectrometry. Gas chromatography-mass spectrometry (GC-MS) analyses of the derivatized total extracts were performed on a HewlettPackard model 6890 GC coupled to Hewlett-Packard model 5973 mass-selective detector (MSD). The GC separation was achieved on a HP-5 fused silica capillary column (25 m × 0.25 mm i.d., 0.5 µm film thickness) with a GC oven temperature program: temperature hold at 50 °C for 2 min, increase from 50 to 120 °C at a rate of 30 °C min-1, then further increase from 120 to 300 °C at a rate of 6 °C min-1 for a total run time of 30 min with a final isotherm hold at 300 °C for 16 min. The sample was injected on a splitless mode with the injector temperature at 280 °C. The mass spectrometer was operated on the electron impact (EI) mode at 70 eV and scanned from 50 to 650 Da. Data were acquired and processed with the Chemstation software. Individual compounds were identified by comparison of mass spectra with literature and library data, comparison with authentic standards, and interpretation of mass spectrometric fragmentation patterns. GC-MS response factors were determined using authentic standards. About 30 cm2 of blank filter was spiked with 100-200 ng of each standard and treated as a real sample. This recovery experiment was repeated three times. The results showed that average recoveries of the 66 standards, including sugars, n-alkanes, fatty alcohols, fatty acids, polyols, polyacids, dicarboxylic acids, ligneous compounds, and sterols, were better than 80% except for the low molecular weight n-alkane (C18), whose recovery was less than 70%. Most of the target compounds were not detected in both the field and the laboratory blank filters, except for fatty acids C16:0 and C18:0, which were less than 2% of abundance of the compounds in real samples. The data reported here were corrected for the field blanks but not corrected for the recoveries.
Results and Discussion A homologous series of seven compound classes, which are n-alkanes, n-alcohols, fatty acids and dicarboxylic acids, saccharides, polyols/polyacids, and lignins/sterols, were detected in the aerosol samples. Concentrations of all of the
FIGURE 1. Concentrations of lipids in the summer and winter. compounds are presented in Table 2 as their range, mean, and standard deviation values (STD), together with carbon preference index (CPI) (18, 19). Results of the aerosol mass and the abundance of total identified organic compounds relative to particulate matter are also shown in the table. Aerosol Mass and Total Amount of the Identified Compounds. The daytime aerosol mass was l28 ( 58 µg m-3 for the summer versus 124 ( 22 µg m-3 in the winter, whereas the nighttime aerosol mass was l35 ( 48 µg m-3 in the summer versus 113 ( 42 µg m-3 in the winter (Table 2). Among the seven identified compound classes, fatty acids were the most abundant, followed by sugars, dicarboxylic acids, and nalkanes. The other three classes of compounds, i.e., alcohols, polyols/polyacids, and lignins/sterols, were less abundant (Figure 1). Total daytime concentrations of the seven compound classes were 807 ( 290 ng m-3 in the summer and 1082 ( 351 ng m-3 in the winter, accounting for 0.77 ( 0.39% and 0.86 ( 0.17% of the particle mass, respectively. The total nighttime concentrations were 1068 ( 415 ng m-3 in the summer versus 1520 ( 938 ng m-3 in the winter, contributing to 0.86 ( 0.31% and 1.25 ( 0.45% of the particle mass, respectively (Table 2). n-Alkanes and Unresolved Complex Mixtures of Hydrocarbons. Normal alkanes were detected in a range of C18-C36. The average concentration of total n-alkanes was 69 ng m-3 in the summer with a maximum at C29, while the average concentration of the total n-alkanes in the winter was 225 ng m-3 with a maximum at C22/C23 (Figures 2a and 2b). The concentration of the total identified n-alkanes was similar to that in Qingdao, China (12) but lower than that in another Chinese mega-city, Guangzhou (13). The CPI (concentration ratio of odd to even carbon number n-alkanes) values of n-alkanes in the summer ranged from 1.66 to 7.05 with an average of 3.46 in the daytime and from 1.59 to 2.64 with an average of 2.03 in the nighttime, while the CPI value in winter was 1.34 ( 0.39 in the daytime versus 1.16 ( 0.03 in the nighttime (Table 2). The CPI indices of the summer aerosols in Nanjing are similar to Qingdao (1.74-5.20, average VOL. 39, NO. 19, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Concentrations of Organic Compounds in Nanjing Aerosols (PM2.5), ng m-3 summer
winter
daytime compound
range
mean
nighttime STD
range
mean
daytime STD
nighttime
range
mean
STD
range
mean
STD
1.59 2.88 6.61 14.2 22.4 23.7 19.6 19.4 12.6 10.8 6.62 10.4 3.95 7.88 2.50 3.35 1.45 1.56 0.34 172 1.34
1.35 0.77 2.17 4.86 7.49 7.70 6.21 6.21 4.36 3.07 2.36 2.96 1.36 2.16 0.91 0.96 0.46 0.54 0.42 53.3 0.39
0.00-10.3 1.63-19.0 3.95-39.3 6.13-60.1 8.17-71.8 7.65-65.5 6.10-50.9 5.65-45.4 3.2-30.2 3.62-23.3 1.82-15.0 3.27-23.2 1.41-8.40 2.83-15.3 0.78-5.48 1.15-8.51 0.54-5.13 0.78-5.76 0.35-2.31 61.0-503 1.11-1.21
2.01 8.95 19.4 32.5 40.0 37.1 28.9 25.7 17.7 13.4 8.88 13.9 5.00 9.39 3.24 4.91 2.55 2.88 1.27 278 1.16
3.79 6.96 13.9 22.2 25.9 23.2 17.5 15.2 10.2 7.39 5.02 7.81 2.52 4.53 1.67 2.63 1.61 2.05 0.74 172 0.03
octadecane nonadecane eicosane heneicosane docosane tricosane tetracosane pentacosane hexacosane heptcosane octacosane nonacosane triacontane hentriacontane dotriacontane tritriacontane tetratriacontane pentatriaconsane hexatriacontane subtotal CPIa
0.00-1.19
0.17
0.45
I. n-Alkanes 0.00-2.00 0.33 0.82
0.00-0.50 0.00-0.90 0.00-1.37 1.35-1.94 1.07-1.84 2.38-7.16 1.23-2.61 3.09-18.8 1.83-4.06 7.82-35.5 1.25-3.34 4.00-20.5 0.99-2.08 1.58-9.71 0.00-1.56 0.00-3.04 0.00-1.24 30.2-110 1.66-7.05
0.13 0.45 0.76 1.62 1.52 3.75 2.02 6.5 2.84 17.5 2.00 7.96 1.46 3.36 0.78 1.23 0.43 54.5 3.46
0.22 0.27 0.40 0.20 0.29 1.62 0.53 5.51 0.84 11.3 0.73 5.94 0.44 3.01 0.63 1.15 0.48 29.3 1.69
0.00-0.74 0.00-1.26 0.71-2.78 1.53-5.46 1.77-7.11 3.58-13.6 2.66-8.79 4.83-12.4 2.68-9.21 11.7-29.1 1.68-7.41 4.88-16.7 1.02-4.71 2.01-7.72 1.07-4.17 1.20-4.76 0.00-2.06 43.4-126 1.59-2.64
0.28 0.46 0.75 1.35 1.88 3.75 2.38 3.6 2.94 6.55 2.37 4.64 1.58 2.19 1.14 1.34 0.92 34.5 0.39
0.00-4.39 1.83-4.30 3.97-10.4 9.21-24.1 13.8-36.8 13.9-36.7 11.4-28.9 11.9-29.6 6.04-18.5 7.29-15.2 3.93-10.5 6.82-15.2 2.19-5.80 5.14-11.3 1.47-3.89 2.19-4.45 0.89-1.99 0.95-2.56 0.00-0.86 112-265 1.18-1.44
tricosane pentacosane heptacosane nonacosane hentriacontane tritriacontane pentatriacontane subtotal
0.27-0.96 1.04-5.27 1.12-16.0 5.27-32.8 2.74-18.6 0.31-8.35 0.00-2.17 12.3-83.5
0.47 1.98 4.07 15.1 6.23 2.23 0.62 30.7
0.22 1.48 5.31 10.8 5.69 2.82 0.76 25.6
Plant Wax Alkanesb 0.19-0.61 0.37 0.16 1.36-5.69 2.82 1.67 1.23-4.39 2.83 1.16 8.34-20.7 12.7 4.59 3.05-10.6 5.59 2.80 0.17-3.91 1.48 1.3 0.66-2.27 1.38 0.63 16.3-46.1 27.2 10.6
1.27-4.23 1.95-5.84 0.02-2.59 3.28-7.04 2.98-6.67 0.87-1.85 0.04-1.59 12.1-27.4
2.64 3.25 1.16 5.07 4.66 1.38 0.66 18.8
1.04 1.28 0.97 1.32 1.2 0.35 0.54 5.17
0.51-4.53 0.84-4.85 0.00-1.11 1.66-11.8 1.74-8.51 0.49-3.33 0.07-2.60 6.84-34.2
2.64 2.43 0.3 6.98 5.27 2.02 0.97 20.6
1.47 1.5 0.43 4.08 2.45 1.01 0.94 11.0
5.46 0.32 6.83 3.56 114 3.7 51.8 2.36 8.97 4.02 13.8 10.8 20.4 5.39 13.0 2.86 15.6 4.48 31.0 2.72 16.8
3.33 0.85 3.99 2.03 67.6 2.04 31 1.37 5.25 2.47 8.17 6.58 12.4 3.53 8.22 1.75 9.72 3.03 19.6 1.76 11.0
0.32 0.68 1.63 3.07 3.76 7.36 5.33 8.48 5.96 17.9 4.31 9.18 2.87 4.25 2.68 3.27 1.09 82.5 2.03
II. Fatty Acids dodecanoic acid tridecanoic acid tetradecanoic acid pentadeconoic acid hexadecanoic acid heptadecanoic acid octadeconoic acid nonadeconoic acid eicosanoic acid heneicosanoic acid docosanoic acid tricosanoic acid tetracosanoic acid pentacosanoic acid hexacosanoic acid heptacosanoic acid octacosanoic acid nonacosanoic acid triacontanoic acid hentriacontanoic acid dotriacontanoic acid tetracontanoic acid subtotal CPIa octadecenoic acid eicosenoic acid docosenoic acid subtotal total aliphatic acids
7432
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0.00-5.51
1.68
2.40
Saturated 0.00-6.44 1.90
2.55
0.00-7.65
4.99
2.43
0.00-4.99 0.00-2.63 27.7-44.7 1.03-2.26 12.9-24.3 0.49-0.88 1.94-4.25 0.66-1.46 3.23-9.69 2.03-8.44 7.11-36.5 1.93-9.37 5.05-33.5 2.53-11.4 8.83-51.4 4.19-15.4 14.8-97.9 0.00-8.96 7.96-35.4 0.00-5.23 121-390 5.33-8.22
2.79 1.58 35.8 1.49 17.8 0.66 2.88 0.95 5.53 3.58 15.9 3.79 14.2 5.47 24.3 7.39 44.4 2.38 16.9 0.75 210 6.85
1.55 0.90 5.79 0.41 4.84 0.14 0.89 0.25 2.14 2.21 11.2 2.64 11.2 3.52 18.1 4.56 34.0 3.54 11.7 1.98 115 0.99
0.00-4.81 1.34-2.66 31.7-99.9 1.12-3.77 14.9-51.8 0.63-1.80 2.58-8.72 1.34-4.62 5.33-19.5 3.40-14.1 13.6-41.9 2.83-11.0 8.09-28.0 4.12-12.1 14.6-54.8 4.67-17.6 24.5-119 2.74-13.6 9.90-91.6 0.00-10.4 180-568 5.88-7.88
1.66 0.56 28.5 1.04 16.1 0.53 2.70 1.30 5.54 4.15 12.4 3.24 7.90 3.14 16.1 5.44 36.2 4.55 31.1 4.05 160 0.76
3.06-7.76 1.65-4.10 56.9-132 1.55-3.92 28.9-60.2 1.08-2.86 3.93-10.2 2.23-4.83 7.25-15.5 4.29-11.8 10.6-23.0 2.99-6.97 7.72-16.1 1.73-3.99 7.38-15.1 0.00-3.92 10.2-24.1 0.00-2.70 4.46-11.6
5.31 3.00 84.5 2.71 43.4 1.77 6.60 3.14 10.4 7.54 14.9 4.19 10.4 2.53 11.0 2.30 16.5 1.72 8.01
1.52 0.86 25.8 0.91 10.5 0.69 2.27 1.12 3.51 2.74 5.06 1.59 3.44 0.91 3.20 1.25 5.46 0.98 2.89
0.00-9.50 0.00-2.25 1.55-13.3 0.74-6.81 26.8-231 0.67-6.28 12.2-109 0.55-4.27 1.97-15.4 0.85-7.24 2.90-25.4 1.99-20.0 5.54-37.7 1.08-10.6 3.13-24.3 0.79-5.17 4.35-29.2 1.25-8.73 9.62-58.3 0.00-5.11 3.91-33.6
187-312 5.36-10.0
245 7.68
53.1 1.65
79.9-613 6.29-9.08
338 7.58
195 1.19
3.74-19.3
9.95
6.54
Unsaturated 7.71-25.1 14.2 6.14
2.19-27.8
17.0
8.48
3.74-19.3 127-408
9.95 220
6.54 121
7.71-25.1 192-583
2.19-27.8 199-338
17.0 262
8.48 56.9
6.42-269 0.00-69.6 0.00-8.31 6.42-288 86.3-890
97.4 9.94 2.60 110 448
103 26.3 3.38 121 310
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 19, 2005
2.99 2.04 61.1 2.21 31.8 1.12 4.95 2.59 10.4 7.09 25.0 5.62 16.0 6.80 29.6 9.02 54.7 6.28 33.6 2.71 316 6.35
14.2 331
6.14 164
TABLE 2. (Continued) summer
winter
daytime compound
range
mean
nighttime STD
range
mean
daytime STD
range
mean
nighttime STD
range
mean
STD
2.16 0.43 0.33 0.28 10.3 1.18 2.3 1.41 5.16 2.07 5.32 0.34 12.5 0.43 23.5 0.78 38.9 0.38 11.6 0.3 120 19.1
5.72 1.13 0.88 0.5 9.56 0.82 1.32 0.92 3.00 1.17 3.07 0.89 6.93 1.13 14.2 1.23 24.8 0.82 8.12 0.78 77.7 6.35
III. Fatty Alcohols tetradecanol pentadecanol hexadecanol heptadecanol octadecanol nonadecanol eicosanol heneicosanol docosanol tricosanol tetracosanol pentacosanol hexacosanol heptacosanol octacosanol nonacosanol triacontanol hentriacontanol dotriacontanol tetracontanol subtotal CPIa
0.00-1.51 1.81-8.18 0.00-2.68 0.00-2.57 0.38-1.98 2.89-6.59 1.48-3.45 3.52-10.0
0.63 5.35 1.65 1.54 1.15 3.96 2.00 5.24
0.60 2.15 0.95 0.86 0.57 1.50 0.70 2.30
6.80-18.0
10.5
3.66
10.9 2.82 44.6 4.24
18.8 0.07 17.6 0.02 6.0
5.77 0.12 5.32 0.05 4.24
58.9 11.8
6.22-34.6 0.00-6.90 51.2-176 5.06-16.5
11.2-28.6 0.00-0.28 9.54-24.1 0.00-0.13 0.00-13.1 49.2-117 8.51-19.7
74.5 13.3
22.6 3.42
0.00-15.1 0.00-2.98 0.00-2.34 0.00-1.27 0.98-24.0 0.00-2.51 0.54-4.64 0.36-2.75 1.22-8.82 0.51-3.47 1.20-9.11 0.00-2.35 3.42-20.3 0.00-2.98 6.11-42.3 0.00-3.05 8.70-70.5 0.00-2.19 0.00-22.0 0.00-2.07 26.0-220 8.23-27.2
73.3 3.96 18.9 16.9 6.40 1.46 13.2 4.18 138
26.0 1.22 4.53 4.12 2.01 0.28 8.58 0.97 27.3
IV. Saccharides 109-355 228 110 2.31-8.70 4.78 2.62 6.19-80.3 30.9 28.7 8.10-51.9 21.6 17.0 1.59-10.6 4.97 3.46 0.76-3.71 2.11 1.27 1.43-32.8 9.44 12.1 0.90-8.43 3.42 3.02 132-497 305 166
161-313 3.85-10.4 8.21-22.8 9.19-20.6 2.64-7.02 1.14-3.38 7.82-28.0 1.95-4.76 196-390
238 6.88 14.0 14.0 4.10 1.85 14.5 3.32 297
66.6 2.19 4.89 4.34 1.51 0.76 6.95 1.04 81.8
83.8-484 2.36-13.6 3.84-18.1 2.89-20.51 1.24-5.23 0.57-4.53 3.19-16.5 1.21-3.22 99.1-554
297 8.57 12.3 13.3 3.52 2.30 10.9 2.34 350
143 4.34 5.43 6.56 1.54 1.29 4.70 0.89 164
19.2-98.6 0.00-55.9 0.00-46.9 0.00-3.68 0.00-30.5
54.6 24.7 10.1 0.53 19.8
30.3 20.1 18.5 1.39 10.4
V. Dicarboxylic Acids 18.3-70.5 50.5 17.9 0.00-34.8 16.7 16.4 0.00-15.8 2.63 6.44 0.00-3.39 0.57 1.39 0.00-26.1 10.4 9.88
15.0-90.2 4.77-32.9
38.3 17.3
25 9.3
7.11-135 2.77-41.3
54.7 17.4
50.7 14
0.00-77.8 0.00-36.4
32.3 11.6
30.2 12.7
9.12-69.7 0.00-56.8
43.9 17.4
23 22.7
0.00-101
20.6
38.9
11.0-70.5 0.00-137 1.46-13.0 0.00-6.33 59.5-508
39.2 37.7 5.85 2.30 215
19.6 60.7 3.84 2.46 152
0.00-39.8 0.00-27.8 7.88-29.9 0.00-97.4 5.72-21.4 0.00-0.81 84.4-263
0.00-85.1 17.4-64.1 3.21-153 7.47-15.6 0.00-14.3 62.6-425
12.9 32.4 42.2 11.2 4.42 203
31.9 19.1 53.4 3.16 6.50 144
0.00-15.3 6.24-36.4 0.00-143 1.68-30.4 0.00-33.3 32.6-461
2.18 19.9 41.7 13.6 12.9 223
5.76 11.5 54.2 10.6 16.3 166
26.1 7.87 5.73 0.90 1.25 41.8
14.6 5.34 5.21 2.39 1.15 23.7
6.19 4.34 24.6 23.4 59.0 1520 113 1.25
3.83 3.14 18.6 13.0 37.8 938 42.2 0.45
0.00-1.38 1.24-3.03 0.00-0.30 1.52-4.16 0.00-1.82 1.76-3.97 0.00-0.87 1.50-10.9 0.00-2.71 3.90-49.0 0.00-4.31 6.62-52.7 0.00-11.6 7.37-48.2
0.47 2.07 0.04 2.54 0.74 2.90 0.18 4.11 1.13 16.9 1.06 24.3 3.32 21.8
0.60 0.75 0.11 0.83 0.69 0.86 0.34 3.17 1.08 15.1 1.62 15.4 4.89 13.6
0.00-12.0
4.78
5.25
26.9-199 6.47-38.8
86.4 16.9
levoglucosan arabitol fructose glucose mannitol inositol sucrose trehalose subtotal
32.7-113 2.51-5.70 12.7-25.0 11.8-24.6 3.20-9.12 1.06-1.97 2.14-27.9 2.87-5.68 114-189
succinic acid glutaric acid adipic acid pimelic acid azelaic acid sebacic acid undecanedioic acid dodecanedioic acid phthalic acid maleic acid fumaric acid iC6c subtotal
0.00-2.16 1.01-1.74
0.86 1.41
0.82 0.31
1.55-4.26 0.00-2.83 1.75-4.33 0.00-1.91 2.47-6.79 0.00-1.94 6.53-21.0 0.00-3.34 13.4-34.5 0.00-11.0 12.1-52.0
2.87 1.46 2.89 0.7 3.8 1.19 12.3 1.01 24.8 4.68 25.1
1.04 0.96 0.86 0.86 1.58 0.72 5.23 1.58 9.67 4.49 14.4
13 1.15 97.2 9.80
17.6 4.63 19.4 27.7 14.1 0.14 164
15.9 11.34 8.53 42.2 5.15 0.33 67.3
glycerol glyceric acid malic acid tartaric acid citric acid subtotal
12.1-220 1.04-22.2 1.89-31.6
56.5 10.7 14.4
74.2 7.82 11.9
VI. Polyols and Polyacids 26.0-76.3 44.9 18.6 12.7-36.1 1.32-17.4 6.76 5.65 4.60-11.6 2.60-18.1 8.06 5.39 3.57-7.05
25.0 7.88 5.90
9.23 2.72 1.35
2.50-5.69 22.5-232
3.59 85.1
1.14 73.0
0.00-6.09 33.7-86.0
2.36 22.3
1.36-4.06 24.4-56.6
2.65 41.4
0.87 11.1
8.42-48.4 3.36-19.4 1.18-16.9 0.00-6.32 0.00-3.05 13.7-84.6
vanillic acid syringic acid dehydroabietic acid β-sitosterol subtotal total particle mass, µg m-3 total organic/PM, %
0.23-0.44 0.13-0.26 1.30-3.07 2.84-8.96 5.27-12.4 485-1404 56.0-187 0.26-1.19
0.36 0.19 2.27 4.44 7.25 807 128 0.77
0.08 0.05 0.63 2.09 2.52 290 57.8 0.39
VII. Lignins and Sterols 0.42-2.60 1.35 0.99 0.23-2.03 0.96 0.81 2.74-25.5 13.5 9.98 3.92-24.4 10.2 7.93 7.34-54.1 26.0 19.2 573-1643 1068 415 43.0-176 135 48.1 0.47-1.33 0.86 0.31
2.52-6.38 1.04-3.85 6.11-14.9 5.44-10.7 15.8-35.6 712-1560 97.0-162 0.56-1.06
3.98 2.32 9.63 8.69 24.6 1082 124 0.86
1.33 0.93 3.39 1.84 6.53 351 22.1 0.17
0.92-11.0 0.48-8.83 4.06-57.9 6.36-42.0 11.8-120 331-2729 40.0-153 0.78-1.96
2.67 62.4
a CPI, carbon preference index: (C 19 + C21 + C23 + ‚‚‚ + C35)/(C18 + C20 + C22 + ‚‚‚ + C34) for n-alkanes, (C14+ C16 + C18 + ‚‚‚ + C32)/(C13 + C15 + C17 + ‚‚‚ C31) for fatty acids, (C16 + C18+ C20 + ‚‚‚ + C32)/(C15 + C17 + C19 + ‚‚‚ + C31) for fatty alcohols. b Calculated as the excess odd homologues - adjacent even homologues average (22). c Isomer of adipic acid.
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FIGURE 2. Molecular distributions of lipids. 2.82) (12) but higher than Guangzhou and Hong Kong (0.911.8, average 1.2) (13, 20). As for the winter aerosols in Nanjing, the CPI indices are very close to those cities. The CPI values of Nanjing aerosols suggest that distribution patterns of the n-alkane for summer aerosols were clearly affected by emission from vegetation, whereas the patterns for winter samples were dominated by the emissions from incomplete combustion of fossil fuels. The n-alkanes in both seasons showed higher CPI values in the daytime and lower CPI values in the nighttime. Difference in inversion height can change the absolute concentrations of n-alkanes but do not change their relative abundances. Therefore, the higher values of the CPI were mainly attributed to more emissions of n-alkanes from biogenic sources during the daytime. There is no correlation between the amounts of total n-alkanes and the CPI indices. Plant wax n-alkanes are calculated as the excess odd homologues - adjacent even homologues (21, 22) and shown in Table 2. These n-alkanes are attributable to vascular plant waxes. In the summer, the average concentration of the total plant wax n-alkanes was 30.7 ( 25.6 ng m-3 in the daytime versus 27.2 ( 10.6 ng m-3 in the nighttime, while in the winter the total amount of the plant wax n-alkanes was 18.8 ( 5.17 ng m-3 in the daytime versus 20.6 ( 11.0 ng m-3 in the nighttime. An unresolved complex mixture (UCM) of hydrocarbons was detected as a hump in the aliphatic hydrocarbon fraction separated from the Nanjng aerosols. The UCM is composed 7434
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of positional isomers of branched and/or cyclic hydrocarbons with different carbon numbers (22, 23). As reported by Peters and Moldowan (24), UCM hydrocarbons are abundantly present in crude oil. Many studies have reported that UCM hydrocarbons can be derived from incomplete combustion of fossil fuels and lubricant in engine exhaust (25, 26) and are found in atmospheric aerosols collected from marine and urban areas (18-21, 23, 27, 28). Concentrations of UCM hydrocarbons in Nanjing aerosols ranged from 83 to 427 ng m-3 with an average of 198 ng m-3 in the summer and from 271 to 2342 ng m-3 with an average of 1048 ng m-3 in the winter. Such a significant seasonal difference is probably related to a large usage of coal burning in the winter and frequent development of inversion layers in the atmosphere. The average concentration of the UCM hydrocarbons during the winter was higher than that in urban Tokyo (e.g., 270-3000 ng m-3, average 880 ng m-3) (21). As shown in Figure 1, concentrations of UCM hydrocarbons in Nanjing aerosols in the daytime were lower than those in the nighttime. Vertical mixing of the air near the ground is much stronger in the daytime than in the nighttime, which could dilute the concentrations of the compounds in the air close to the ground surface in the daytime. Another potential cause is that the usage of heavy-duty diesel trucks for transportation is only permitted at night, which leads to more pollutants including UCM hydrocarbons emitted to the nocturnal air. Interestingly, the UCM concentrations showed a significant negative correlation with values of the [(CPI of n-alkane) -
FIGURE 3. Relationship between the concentrations of the unresolved complex mixture (UCM) of hydrocarbons and (CPI index of n-alkanes) - 1. 1] (R2 ) 0.75, Figure 3). A similar negative relationship was also found in urban aerosols from Tokyo (21) and marine aerosols from the western North Pacific (23). Fatty Acids. A homologous series of fatty acids (C12-C34) was detected in the aerosol samples. A significant seasonal difference in the concentrations of the total fatty acids was found. Concentrations of the total fatty acids in the summer ranged from 127 to 408 ng m-3 with an average of 220 ng m-3 in the daytime and from 192 to 583 ng m-3 with an average of 331 ng m-3 in the nighttime. The winter samples showed that the total amounts of fatty acids varied from 199 to 338 ng m-3 with an average of 262 ng m-3 in the daytime and from 86.3 to 890 ng m-3 with an average of 448 ng m-3 in the nighttime. The concentrations of fatty acids in the Nanjing urban area are in the range of the concentrations reported from other Chinese urban aerosols (14-11 000 ng m-3) (29, 30) and also close to those of the continental aerosols from Japan (31-1110 ng m-3, average 330 ng m-3) (23) and the United States (22-670 ng m-3) (31). There was a significant difference in the total amounts of fatty acids between daytime and nighttime (Figure 1). Lower molecular weight (LMW) fatty acids (C12-C19) are derived from vascular plants and microbial sources as well as marine phytoplankton, while higher molecular weight (HMW) fatty acids (C20-C34) are characteristic of terrestrial higher plant waxes (23, 32-34). As for the summer samples, HMW fatty acids (181 ng m-3, on average, thereinafter) are more abundant than LMW fatty acids (82.4 ng m-3). As for the winter samples, in contrast, HMW fatty acids (125 ng m-3) are less abundant than LMW fatty acids (167 ng m-3). It can be interpreted that terrestrial higher plants are more active in photosynthesis during summer and could release more plant waxes including HMW fatty acids. Conversely, leaves of deciduous trees fall in the autumn, and active plant sources for wax emissions are limited in the winter. Molecular distributions of the saturated fatty acids showed a strong even carbon number predominance with two maxima at C16 and C30 (Figures 2c and 2d). CPI values (even-to-odd) of the fatty acids are 6.60 in the summer and 7.63 in the winter. A similar bimodal molecular distribution has been reported in continental (28, 31) and marine aerosols (23, 35-37). Unsaturated fatty acid C18:1 was detectable in all of the samples whose concentrations were found to be lower in the summer than those in the winter. However, minor amounts of C20:1 and C22:1 were detectable only in the winter nighttime. Such temporal distributions of the three alkenoic acids suggest that unsaturated fatty acids are easily oxidized once emitted to the atmosphere (38). No lower molecular weight alkenoic acids (i.e.,
