Environ. Sci. Technol. 2002, 36, 1389-1395
Speciated Ambient Carbonyls in Rio de Janeiro, Brazil D A N I E L G R O S J E A N , * ,† ERIC GROSJEAN,† AND LINO F. R. MOREIRA‡ DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, California 93003, and Setor de Biotecnologia e Ecossistemas, Centro de Pesquisas (CENPES), Petro´leo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, RJ, Brazil
Carbonyls in urban air continue to receive scientific and regulatory attention as toxic air contaminants and for their important role in photochemical smog. However, few data are available for speciated carbonyls in urban air. Ambient concentrations of up to 61 carbonyls have been measured in Rio de Janeiro, Brazil. The most abundant carbonyls were formaldehyde and acetaldehyde (studyaveraged concentrations of 10.8 ( 4.1 and 10.4 ( 4.6 µg m-3, respectively, in samples of 3-h duration collected from May to November 2000 at a downtown location during the morning vehicle commute) followed by acetone, 2-butanone, and benzaldehyde. Ambient concentrations of other carbonyls (except acetophenone) correlated well with those of acetaldehyde and of formaldehyde. This study examines the ambient acetaldehyde/ambient formaldehyde concentration ratio in Brazilian cities since the mid1980s in the context of changes in Brazil’s reliance on ethanol as a vehicle fuel. This ratio has begun to decrease in recent years due to fleet turnover and is likely to decrease further as older cars fueled with ethanol are replaced by lower-emitting models that run on a gasolineethanol blend. The carbonyls measured are ranked with respect to ozone formation potential (using MIR coefficients) and reaction with OH (using carbonyl-OH reaction rate constants). Ozone formation is dominated by formaldehyde (43% of total) followed by acetaldehyde (32%) and methylglyoxal (8%); other carbonyls each contributed e4% of total. For reaction with OH, acetaldehyde ranks first closely followed by formaldehyde.
Introduction The importance of carbonyls in urban air quality and atmospheric chemistry has long been recognized (1). Carbonyls are emitted by vehicles and by stationary sources, including indoor sources (1, 2). They also form as products of the atmospheric oxidation of hydrocarbons and other volatile organic compounds (3-5). Carbonyls in urban air continue to receive scientific and regulatory attention as toxic air contaminants, mutagens, and carcinogens (6-8) and for their role as photochemical precursors to free radicals, ozone, and peroxyacyl nitrates (9-12). Vehicle emissions are a major source of carbonyls in urban air (1). Information on the nature and magnitude of vehicle emissions of speciated carbonyls * Corresponding author phone: (805) 644-0125; fax: (805) 6440142; e-mail:
[email protected]). † DGA, Inc. ‡ Petro ´ leo Brasileiro S.A. 10.1021/es0111232 CCC: $22.00 Published on Web 02/21/2002
2002 American Chemical Society
is available from dynamometer studies (13, 14) and from measurements made in highway tunnels (15-19). Ambient concentrations of formaldehyde and acetaldehyde in urban air have been measured many times (20-22). However, ambient levels of other carbonyls have received much less attention (23). This is particularly true outside North America, Europe, and Japan, and little or no information is available regarding speciated carbonyls in the atmosphere of many of the world’s largest urban enters. We report ambient concentrations of up to 61 carbonyls measured at a downtown location in Rio de Janeiro, Brazil. Rio de Janeiro (ca. 23° S, 43° W) is one of the largest cities in the southern hemisphere and is the second largest city in Brazil. The metropolitan area is ∼6500 km2 and has a population of ∼11 million. There are ∼1.2 million vehicles in the city of Rio de Janeiro and ∼2.3 million vehicles in the metropolitan area. The vehicle fuels used in Rio de Janeiro reflect Brazil’s heavy reliance on ethanol made from sugar cane. Brazil is the only country in the world where neat ethanol is used nationwide as a vehicle fuel. Ethanol is also used as an additive to gasoline, and this at higher concentrations than anywhere else in the world. Thus, the Rio de Janeiro metropolitan area fleet includes ∼410,500 light-duty vehicles (17.9% of total) that run on ethanol, ∼1,763,000 lightduty vehicles (76.9% of total) that run on a gasoline-ethanol blend (∼20 vol % ethanol at the time of our study), and ∼118,500 diesel-powered buses and trucks (5.2% of total; the diesel fuel contains no ethanol). The extensive public transportation system in Rio de Janeiro consists mostly of diesel-powered buses, which often account for G30% of the total vehicle traffic on major arteries in the downtown area. Information regarding ambient air quality in Rio de Janeiro is available for criteria pollutants, which are monitored by the state environmental agency at several locations (24, 25), for particulate matter (26-30), for gas phase toxic contaminants (31), and for speciated C1-C10 hydrocarbons (32). Indoor air quality has also been studied (33). Limited information is available for outdoor and indoor levels of formaldehyde and acetaldehyde (see Results and Discussion). No comprehensive study of ambient speciated carbonyls has been carried out in Rio de Janeiro prior to this work.
Experimental Methods Sampling Locations. All but one sample were collected at the air quality monitoring station operated in downtown Rio de Janeiro by the state environmental agency, Fundac¸ a˜o Estadual de Engenharia do Meio Ambiente do Estado da Rio de Janeiro (FEEMA). The FEEMA station is located near the intersection of Avenida Presidente Vargas, the largest artery in downtown Rio de Janeiro (seven lanes in each direction), and Rua Tome de Souza. One sample was collected in Copacabana, on the ninth floor of a building located on Avenida Atlantica, which runs the length of Copacabana Beach. For the samples collected at the downtown FEEMA station, where air quality is strongly influenced by vehicle traffic on Avenida Presidente Vargas and numerous other arteries and streets in the downtown area, we elected to collect ambient samples at the time vehicle emissions had the greatest impact on ambient air quality. Thus, we collected samples every two weeks during the six-month period of May 3-Nov 1, 2000. This period brackets the winter season (ca. June 21-Sept 21) when meteorological conditions are typically most conducive to poor air quality (i.e., poor ventilation resulting from a combination of low mixing height and low wind speed, as indicated by examination of ∼15 years of meteorological data for the Rio de Janeiro area). The sampling period was selected after data made available by VOL. 36, NO. 7, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FEEMA for the preceding winter had been studied. Parameters measured by FEEMA at the downtown monitoring station included temperature, humidity, wind speed, wind direction, CO, NO, NOx, O3, SO2, total hydrocarbons, methane, total non-methane hydrocarbons, and particulate matter. From hourly concentrations reported by FEEMA for the period May 12-August 31, 1999, we constructed composite diurnal profiles for CO, NO, NOx, and total non-methane hydrocarbons, and we used these composite diurnal profiles as indicators of vehicle traffic in the downtown area. On the average, ambient concentrations of CO, NO, NOx, and total non-methane hydrocarbons were highest in the morning and evening hours. Thus, the period from 8:00 a.m. to 11:00 a.m. was selected for collection of carbonyl samples (with two exceptions: the first sample collected at the FEEMA station was collected from 10:00 a.m. to 12:00 noon, and the sample collected at Copacabana was collected for 2 h in the afternoon). Vehicle traffic at the time of carbonyl sampling was moderate to heavy at the downtown FEEMA station and was heavy in Copacabana (stop-and-go traffic on Avenida Atlantica, mostly light-duty vehicles, and on Avenida N. S. de Copacabana, where diesel-powered buses accounted for ∼40-50% of total traffic). Ambient temperatures were 20 °C in Copacabana and 18-27 °C (initial T) and 21-32 °C (final T) at the downtown FEEMA station. Earlier (1998) traffic counts made on Avenida Presidente Vargas near the location of the FEEMA station indicated that, for the 1-h period of 8:30-9:30 a.m., total traffic was ∼6050 vehicles, of which 4660 were light-duty vehicles, 1340 were buses, and 50 were trucks. Carbonyl Sampling and Analysis. Carbonyl samples were collected by drawing air through silica gel cartridges coated with 2,4-dinitrophenylhydrazine (DNPH). The DNPH-coated cartridges were purchased from Waters Corp. All samples were collected downstream of a KI oxidant scrubber (Waters Corp.) that was connected to the cartridge by a short piece of Teflon tubing (∼2.5-cm length and 0.6-cm diameter). The sampling flow rates were 545-689 mL/min (measured with a flowmeter calibrated using a certified, NIST-traceable Humonics model 650 flow calibrator). Samples and field controls (two at the FEEMA station and one in Copacabana) were eluted with acetonitrile, and aliquots of the extracts were analyzed by liquid chromatography with detection by diode array ultraviolet-visible spectroscopy and by atmospheric pressure negative chemical ionization mass spectrometry (34). The overall analytical protocol and instrument operating conditions have been described in detail by Grosjean et al. (34). Carbonyls were positively identified by matching the retention times, UV-visible absorption spectra, and negative chemical ionization mass spectra of their DNPH derivatives to those of ∼150 carbonyl-DNPH reference standards synthesized in our laboratory (34-36). Quantitative analysis involved the use of response factors measured using carbonyl-DNPH reference standards (23, 34-36). Three samples were analyzed twice, and the relative standard deviations (RSD) for these replicate analyses were 2-4% for all carbonyls.
Results and Discussion Carbonyls Identified and Their Ambient Concentrations. Sixty-one carbonyls have been identified in Rio de Janeiro ambient air. Concentrations of the lower molecular weight (MW) carbonyls have been measured for 32 compounds in all samples and are listed in Table 1. The higher MW carbonyls were present in all samples but were generally less abundant. Their concentrations have been calculated for 29 compounds in one sample and are listed in Table 2. Of the 32 carbonyls listed in Table 1, two were detected in only two samples (indanone and trans-cinnamaldehyde), and one was detected in only one sample (an aromatic carbonyl, isomer not specified). The other carbonyls were 1390
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detected in all samples and included 7 saturated aliphatic aldehydes, 4 saturated aliphatic ketones, 3 saturated aliphatic carbonyls (1 C5 and 2 C6 isomers), 3 unsaturated carbonyls (acrolein, methacrolein, and crotonaldehyde), 2 dicarbonyls (glyoxal and methylglyoxal), and 10 aromatic carbonyls. Average carbonyl concentrations calculated from data for the 3-h samples collected at the downtown location are given in Table 3. Table 3 also includes the corresponding RSD (a measure of sample-to-sample variability) and a ranking of carbonyls in order of decreasing abundance (mass concentration basis). Formaldehyde (study-averaged concentration ) 10.8 ( 4.1 µg m-3) and acetaldehyde (10.4 ( 4.6 µg m-3) were the most abundant carbonyls on a mass concentration basis, followed by acetone, 2-butanone, and benzaldehyde. On average, formaldehyde and acetaldehyde together accounted for 61% (mass concentration basis) of the sum of the concentrations of the 32 carbonyls listed in Table 1. The acetaldehyde/formaldehyde concentration ratio (see discussion later in this section) averaged 0.96 on a mass concentration basis and 0.66 on a mixing ratio basis (ppb/ppb). The entries ALP ISM (aliphatic isomer) and ARM ISM (aromatic isomer) in Tables 1 and 2 reflect the current limitation of our library of reference compounds; that is the MW and chemical functionality (saturated aliphatic, unsaturated aliphatic, dicarbonyl, aromatic) of the compound could be determined, but no reference standard was available for positive identification of the isomer(s) present in the sample. Table 2 contains more ISM (isomers) entries than Table 1 because the number of possible isomers increases with carbon number. Isomers that have nearly identical retention times also have nearly identical response factors (23, 34-36), so concentration of isomers that were not positively identified could be reported using the measured response factor of the closest-eluting isomer for which a reference standard was available. The higher MW carbonyls (Table 2) included 6 saturated aliphatic aldehydes (from heptanal to dodecanal), 1 saturated aliphatic ketone (2-decanone), 11 saturated aliphatic carbonyls (1 C7, 3 C8, 3 C9, 1 C10, 1 C11, 1 C12, and 1 C13 isomer), 6 aliphatic dicarbonyls (from 2-oxobutanal to a C10 isomer), and 5 aromatic carbonyls. The sum of the ambient concentrations of these 29 compounds was ∼9.7 µg m-3. The sum of the ambient concentrations of the lower MW carbonyls measured in the same sample (Table 1) was 18.75 µg m-3; that is, for that sample the higher MW carbonyls listed in Table 2 accounted for 34% of the total measured carbonyls on a mass concentration basis. The most abundant high MW carbonyls were nonanal (∼2.1 µg m-3), decanal (∼1.5 µg m-3), a C8 saturated aliphatic isomer (∼0.9 µg m-3), and three aromatic carbonyls (each ∼0.7 µg m-3) including two trimethylbenzaldehyde isomers. Although our study covered a 6-month period, the sampling frequency was low (one sample every other week), and as a result no seasonal variation is apparent from the data in Table 1. During the period studied, May-Oct 2000, ambient levels of formaldehyde, acetaldehyde, acetone, and total measured carbonyls varied within factors of ∼4-5 (e.g., from 15.9 to 72.4 µg m-3 for the sum of the concentration of the carbonyls listed in Table 1). These sample-to-sample variations reflect variations in meteorology and in the relative contribution of the various sources of carbonyls. Sources of carbonyls in Rio de Janeiro ambient air are examined in more detail below. Correlations among Carbonyls. We carried out linear regressions of the type [carbonyl A] versus [carbonyl B], where [carbonyl A (or B)] is the ambient concentration, for the carbonyls listed in Table 1 that were detected in all samples collected between 8:00 a.m. and 11:00 a.m. at the downtown location. These linear regressions (unit-weighted, not forced through the origin, no apparent outliers deleted) yielded
TABLE 1. Concentrations of Carbonyls in Rio de Janeiro Ambient Aira carbonyl concn, µg m-3 date: start time: stope time:
VOL. 36, NO. 7, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
formaldehyde acetaldehyde acetone acrolein propanal crotonaldehyde methacrolein 2-butanone (MEK) butanal and/or isobutanalb benzaldehyde o/m/p-anisaldehyde C5 ALP ISMc isopentanal 2-pentanone glyoxal pentanal acetophenone o-tolualdehyde m-tolualdehyde p-tolualdehyde ARM ISM 1 C6 ALP ISM 1 trans-cinnamaldehyde indanone C6 ALP ISM 2 4-methyl-2-pentanone (MIBK) methyl glyoxal hexanal DMBZ ISM 1 2,5-dimethylbenzaldehyde 2,4-dimethylbenzaldehyde/ISM DMBZ ISM 2 sum a
Oct 2, 1999 May 3, 2000 May 17, 2000 May 31, 2000 June 14, 2000 June 28, 2000 July 12, 2000 July 26, 2000 Aug 9, 2000 Aug 23, 2000 Sept 6, 2000 Sept 20, 2000 Oct 4, 2000 Oct 28, 2000 Nov 2, 2000 2:42 p.m. 9:55 a.m. 7:50 a.m. 8:00 a.m. 8:10 a.m. 8:00 a.m. 7:50 a.m. 8:00 a.m. 8:00 a.m. 8:02 a.m. 8:00 a.m. 8:00 a.m. 8:00 a.m. 8:00 a.m. 8:00 a.m. 4:12 p.m. 12:05 p.m. 10:50 a.m. 11:00 a.m. 11:10 a.m. 11:00 a.m. 10:55 a.m. 11:00 a.m. 11:00 a.m. 11:02 a.m. 11:00 a.m. 11:00 a.m. 11:00 a.m. 11:00 a.m. 11:00 a.m. 6.803 3.426 4.098 0.046 0.331 0.253 0.016 0.049 0.226
34.616 9.790 10.781 0.513 0.867 0.161 0.182 1.321 0.545
19.645 20.627 7.353 2.594 2.288 0.912 0.209 3.630 1.062
8.958 8.497 3.488 0.554 0.731 0.156 0.151 1.202 0.321
8.990 9.408 4.208 0.813 0.797 0.315 0.111 1.300 0.368
11.641 8.493 3.098 0.327 0.546 0.096 0.057 0.427 0.520
13.769 8.735 2.312 0.422 0.556 0.180 0.091 0.728 0.257
7.591 9.006 2.719 0.627 0.674 0.296 0.099 1.150 0.311
16.477 18.253 7.127 1.272 2.212 0.380 0.229 2.592 1.003
12.223 13.737 5.839 1.408 2.004 0.561 0.371 2.677 0.760
5.310 5.265 1.599 0.382 0.392 0.151 0.046 0.546 0.190
8.961 8.945 4.560 0.685 0.946 0.214 0.156 1.287 0.389
5.514 5.442 3.778 0.373 0.632 0.157 0.097 0.822 0.279
9.247 8.136 3.255 0.498 0.789 0.208 0.101 0.857 0.347
12.556 11.102 4.471 0.681 1.068 0.281 0.137 1.179 0.470
0.649
0.749 0.054 0.082 0.232 0.238 0.392 0.297 0.142 0.032 0.190 0.064
3.171 0.086 0.123 0.520 0.642 0.881 0.668 0.123 0.082 0.831 0.279
0.566 0.040 0.058 0.195 0.185 0.291 0.220 0.101 0.042 0.209 0.070
1.210 0.041 0.112 0.293 0.108 0.167 0.127 0.083 0.033 0.305 0.103
0.569 0.073 0.052 0.119 0.113 0.241 0.182 0.073 0.069 0.217 0.073
0.436 0.065 0.034 0.197 0.327 0.454 0.344 0.157 0.033 0.174 0.058
0.649 0.066 0.083 0.144 0.085 0.160 0.121 0.100 0.041 0.184 0.062
1.434 0.097 0.271 0.575 0.476 0.649 0.492 0.070 0.093 0.772 0.259
2.825 0.084 0.096 0.434 0.170 0.284 0.215 0.115 0.063 0.512 0.172
0.473 0.035 0.043 0.105 0.041 0.113 0.086 0.096 0.034 0.124 0.042
0.560 0.040 0.079 0.303 0.126 0.195 0.148 0.061 0.052 0.228 0.076
0.686 0.030 0.055 0.184 0.271 0.433 0.328 0.124 0.065 0.345 0.116
0.929 0.025 0.074 0.250 0.367 0.587 0.445 0.168 0.088 0.468 0.157
0.293
1.897
0.258
0.688
0.291
0.093
0.324
1.729
1.139
0.415
0.780
1.061
0.414
0.033 0.063
1.025 0.063
0.101 0.032
0.138 0.031
0.045 0.024
0.052 0.029
0.031 0.029
0.064 0.055
0.132 0.046
0.095 0.073 0.022 0.032 0.023
0.099 0.032
0.510 0.025 0.048 0.135 0.107 0.208 0.157 0.120 0.038 0.090 0.030 0.020 0.246 0.098 0.021 0.050 0.036
0.020 0.028
0.036 0.039
0.204 0.374 0.428
1.086 0.476 0.010 0.039
2.891 0.478 0.032 0.091
0.800 0.245 0.010 0.057
0.970 0.237 0.009 0.043
0.611 0.182 0.008 0.020
0.704 0.217 0.011 0.077
0.545 0.218 0.033 0.053
1.323 0.418 0.023 0.106
1.267 0.352 0.031 0.060
0.308 0.175 0.006 0.059
1.171 0.244 0.007 0.044
0.769 0.276 0.005 0.048
0.915 0.211 0.010 0.072
1.253 0.296 0.014 0.097
0.214
0.043
0.137
0.040
0.036
0.032
0.049
0.141
0.096
0.130
0.026
0.030
0.023
0.043
0.058
0.375
0.032
0.057
0.028
0.017
0.020
0.044
0.024
0.045
0.043
0.033
0.012
0.015
0.021
0.029
63.319
72.396
27.607
31.060
28.219
30.606
25.567
58.590
47.747
15.928
30.065
20.171
28.174
38.384
0.016 0.016 0.011 0.016 0.131 0.161 0.154 0.229 0.089
18.75
The sample collected on Oct 2, 1999, was collected in Copacabana. All other samples were collected at the FEEMA monitoring station, Avenida Presidente Vargas, in downtown Rio de Janeiro. b The two isomers were not resolved. c ALP, saturated aliphatic; ARM, aromatic; ISM, isomer; DMBZ, dimethylbenzaldehyde.
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TABLE 2. Ambient Concentrations of Higher Molecular Weight Carbonylsa carbonyl
concn, µg m-3
carbonyl
concn, µg m-3
carbonyl
concn, µg m-3
C7 ALP ISM 1 2-oxobutanal ARM ISM 2 biacetyl TMBZ ISM 1 heptanal 2,4,6-trimethylbenzaldehyde/ISM TMBZ ISM 2 2-oxopentanal C8 ALP ISM 1
0.107 0.179 0.742 0.179 0.231 0.082 0.657 0.660 0.151 0.911
2,3-pentanedione C8 ALP ISM 2 C8 ALP ISM 3 octanal C9 ALP ISM 1 C4 SUB BENZ C8 DICARB C9 ALP ISM 2 C9 ALP ISM 3 nonanal
0.058 0.066 0.232 0.095 0.412 0.054 0.086 0.045 0.057 2.089
C10 ALP ISM 1 2-decanone decanal C10 DICARB C11 ALP ISM 1 undecanal C12 ALP ISM 1 dodecanal C13 ALP ISM 1
0.267 0.534 1.471 0.056 0.037 0.113 0.079 0.002 0.003
sum
9.65
a
Sample collected on Oct 2, 1999 in Copacabana. Concentrations of the lower molecular weight carbonyls measured in the same sample are given in Table 1. b ALP, saturated aliphatic; ISM, isomer; ARM, aromatic; TMBZ, trimethylbenzaldehyde; SUB BENZ, substituted benzaldehyde; DICARB, aliphatic dicarbonyl.
TABLE 3. Average Concentrations and Correlation Coefficients for Ambient Carbonyls Measured in 3-h Samples Collected in Rio de Janeiro carbonyl
av concn, RSD, % Nb rankc R(C1)d µg m-3 a
R(C2)e
formaldehyde acetaldehyde acetone acrolein propanal crotonaldehyde methacrolein 2-butanone (MEK) butanal and/or isobutanal benzaldehyde o/m/p-anisaldehyde C5 ALP ISM isopentanal 2-pentanone glyoxal pentanal acetophenone o-tolualdehyde m-tolualdehyde p-tolualdehyde ARM ISM 1 C6 ALP ISM 1 trans-cinnamaldehyde indanone C6 ALP ISM 2 4-methyl-2-pentanone (MIBK) methyl glyoxal hexanal DMBZ ISM 1 2,5-dimethylbenzaldehyde 2,4-dimethylbenzaldehyde/ISM DMBZ ISM 2
10.84 10.43 4.14 0.82 1.05 0.301 0.143 1.415 0.483
38 44 42 77 63 73 61 68 59
13 13 13 13 13 13 13 13 13
1 2 3 8 6 13 18 4 10
(1.00) 0.90 0.74 0.76 0.78 0.71 0.50 0.74 0.85
0.90 (1.00) 0.91 0.91 0.95 0.86 0.68 0.93 0.96
1.078 0.054 0.087 0.266 0.232 0.359 0.272 0.107 0.056 0.343 0.115 0.020 0.694 0.085 0.022 0.140 0.036
84 46 71 58 76 64 64 30 39 69 69
5 27 22 16 17 11 15 21 26 12 20 31 9 23 30 19 28
0.68 0.72 0.55 0.78 0.90 0.89 0.89 0.18 0.72 0.86 0.86
0.83 0.74 0.75 0.93 0.84 0.82 0.82 -0.01 0.74 0.97 0.97
87 20 3 192 34
13 13 13 13 13 13 13 13 13 13 13 1 13 2 2 13 13
0.79
0.94
0.65 0.77
0.70 0.92
1.041 0.273 0.015 0.064
61 34 69 38
13 13 13 13
7 14 32 25
0.79 0.77 0.54 0.62
0.86 0.92 0.72 0.63
0.065
69 13
24
0.54
0.72
0.030
46 13
29
0.77
0.75
sum
34.963
45 13
0.92
0.99
a
Calculated for the 13 samples collected from 8 a.m. to 11 a.m. at the downtown location. b Number of samples in which the carbonyl was detected. c In order of decreasing abundance, mass concentration basis. d Correlation coefficient for linear regression of ambient carbonyl vs ambient formaldehyde. e Correlation coefficient for linear regression of ambient carbonyl vs ambient acetaldehyde.
slopes and their RSD, intercepts and their RSD, and correlation coefficients that we examined for correlations among carbonyls. The correlation coefficients R obtained for regressions of [carbonyl A] versus [formaldehyde] and [carbonyl A] versus [acetaldehyde] are given in Table 3. With the exception of acetophenone, all carbonyls were reasonably well correlated with acetaldehyde, with R > 0.9 for 12 carbonyls (and also for the sum of the carbonyls), R > 0.7 for 14 carbonyls, and R ) 0.63 for 2,5-dimethylbenzaldehyde. With the exception of acetophenone, all carbonyls also correlated 1392
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reasonably well with formaldehyde, with R > 0.9 for 2 carbonyls (acetaldehyde and 2-pentanone, and also for the sum of the carbonyls), R > 0.7 for 18 carbonyls, and R > 0.5 for 7 carbonyls. The large majority of the carbonyls (24 of 28) exhibited better correlation with ambient acetaldehyde than with ambient formaldehyde. The reverse was observed for 2-pentanone, glyoxal, pentanal, and one dimethylbenzaldehyde isomer. Sources of carbonyls in urban air include direct emissions from vehicles, direct emissions from stationary sources, insitu photochemical production from volatile organic compounds emitted by mobile and stationary sources (including hydrocarbons, carbonyls, and ethanol), and carry-over of carbonyls emitted and/or produced in-situ during the preceding day. We sampled ambient carbonyls at a downtown location next to the largest artery, and this during the morning period of heavy weekday vehicle commute. Thus, ambient concentrations of carbonyls were most likely dominated by vehicle emissions. Vehicle emissions of carbonyls include those from cars fueled with ethanol, those from cars fueled with the gasoline-ethanol blend, and those from dieselpowered buses. These three categories of mobile sources have different carbonyl profiles. However, the relative contribution of each type of vehicle to total mobile source emissions of carbonyls was fairly constant from one sampling period to the next (same location, same day of the week, and same time of day). It is therefore reasonable to assume that the overall profile of carbonyl emissions from mobile sources did not change much from one sampling period to the next. Thus, the correlations among ambient carbonyls given in Table 3 may simply reflect the dominance of mobile source emissions together with the fairly uniform fleet composition at the location sampled. A more detailed analysis of our data with respect to sources of carbonyls in Rio de Janeiro, and more specifically mobile sources, must await the results of studies, currently in progress, of vehicle emissions of speciated carbonyls in dynamometer tests and in Rio de Janeiro highway tunnels. Ambient Formaldehyde, Ambient Acetaldehyde, and the Use of Ethanol as a Vehicle Fuel in Brazil. To reduce oil imports following the 1973 oil crisis, and faced with low returns on sugar exports, Brazil initiated in 1975 a program of production, from sugar cane, of ethanol to be used as a vehicle fuel. The first engines designed to use neat ethanol were introduced in 1979, and the same year gasoline was replaced by a gasoline-ethanol blend (15 vol % ethanol in 1979 and ∼22 vol % ethanol thereafter). Sales of new lightduty (LD) vehicles that use ethanol reached a maximum in the late 1980s, accounting for ∼90% of total new car sales in 1986. The fraction of the total LD fleet that uses ethanol correspondingly grew in the early 1980s (ca. 3, 7, 10, 15, 21, and 26% in 1980, 1982, 1983, 1984, 1985, and 1986, respec-
TABLE 4. Summary of Literature Data for Ambient Formaldehyde and Acetaldehyde in Brazilian Cities month/year
location
av concn, ppb formaldehyde acetaldehyde
ratio, acetaldehyde/formaldehydea
ref
Rio de Janeiro 26.4 1.8 4.6 4.1 11.9 11.8 5.5 8.8
37.1 3.7 6.2 4.7 48.2d 9.4 1.9 5.8
1.40 (15) 2.05 (10) 1.34 (2) 1.15 (6) 4.05 (6)d 0.80 (11) 0.34 (1) 0.66 (13)
43 43 45 44 46 33 this study this study
USP campus CETESB Prac¸ a de Correio Congonhas Congonhas Cerqueira Cesar Moo´ ca Cerqueira Cesar six locationsb,c Moo´ ca Cerqueira Cesar Cerqueira Cesar USP campus Cerqueira Cesar USP campus
Sao Paulo 8.8 13.5 5.4 14.5 10.8 15.5 8.5 21.8 9.6 4.2 7.6 5.4 1.3 7.0 4.2
7.6 8.0 16.1 24.2 22.3 24.3 16.2 27.3 19.4 6.1 10.6 7.5 2.8 11.7 9.2
0.86 (8) 0.59 (4) 3.0 (3) 1.67 (26) 2.06 (17) 1.56 (23)f 1.90 (12)f 1.25 (6)f 2.03 (6) 1.45 (179) 1.39 (180) 1.39 (132) 2.15 (60) 1.67 (155) 2.19 (130)
44 44 44 45 48 48 48 48 46 49 49 49 49 49 49
Sept 1988 1995-1996?g 1995-1996?g
Rua Vitoriab Rio Vermelho Baixa dos Sapateiros
Salvador 23.3 2.9 11.0
22.1 3.5 6.3
0.95 (3) 1.20 (17) 0.57 (24)
44 50 50
March 1997-April 1999 April 1997 May-Sept 1999
Rodoviaria Rodoviaria Rodoviaria
Porto Alegre 7.21 15.7 4.59
3.49 17.7 3.85
0.48 (111)h 1.13 (6)h 0.84 (24)i
51, 52 53 51, 52
July 1985 July 1985 Jan 1987 Sept 1987 Jan 1993 Dec 1995 Oct 1999 May-Oct 2000
Vila Isabel PUC campus Gavea R. Cosme Velho six locationsb,c one locationb,e Copacabana Av. Presidente Vargas
June-July 1986 July 1986 Oct 1986 Dec 1988 Sept-Oct 1989 March-April 1990 April 1990 Aug 1990 Jan 1993 1993 1993 Oct 1996-Jan 1997 Oct 1996-Jan 1997 July-Sept 1997 July-Sept 1997
a Ratio (ppb/ppb) of average concentrations; number of measurements given in parentheses. b This study also included indoor measurements that are not listed here. c Locations not listed, outside three restaurants and three offices, one sample per location. d If we omit a high (and perhaps unlikely) concentration of 178 ppb for acetaldehyde in one of the six samples, the average acetaldehyde is 22.3 ppb and the acetaldehyde/ formaldehyde ratio is 2.35. e Location not specified. f Ethanol fuel was replaced during 1990 by a mixture of ethanol, methanol, and gasoline (60, 33, and 7 vol %, respectively). g Year(s) the study took place is not indicated. h A gasoline-MTBE blend (∼14 vol % MTBE) was used during this period. i A gasoline-ethanol blend (∼24 vol % ethanol) was used during this period.
tively), and the rest of the LD fleet was fueled with the gasoline-ethanol blend. Sales of new LD vehicles that use ethanol have decreased steadily since the late 1980s and have been essentially nil (1 (units of ppb/ppb), with average values of up to 3.0. In contrast, the average ratio in 2000 in Rio de Janeiro was only 0.66 (range ) 0.43-0.81 ppb/ppb, n ) 13). This low ratio is VOL. 36, NO. 7, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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consistent with that of 0.84 we measured in Porto Alegre during winter 1999 (51, 52) when the fuels used by the LD fleet in Porto Alegre (ethanol for 20% of the LD fleet and a blend of gasoline and 24 vol % ethanol for the remaining 80% of the LD fleet) were essentially the same as those used in Rio de Janeiro during this study. The recent decrease in the acetaldehyde/formaldehyde ambient concentration ratio is likely to be the result of fleet turnover. Essentially no new cars fueled with ethanol have been sold in Brazil in the past ∼4-5 years, and therefore older ethanol-fueled cars are being replaced by newer vehicles that run on the gasoline-ethanol blend. The acetaldehyde/ formaldehyde emission ratio for LD vehicles that run on the gasoline-ethanol blend is lower than for LD vehicles that run on ethanol, and as a result fleet turnover leads to lower LD vehicle emissions of acetaldehyde relative to those of formaldehyde. Although the Rio de Janeiro LD fleet turnover is currently slow, the ambient acetaldehyde/ambient formaldehyde concentration ratio is likely to continue to show a downward trend in future years. Unless it is offset by a rapid growth of the fleet in the Rio de Janeiro metropolitan area, fleet turnover is also predicted to result in a decline in overall vehicle emissions and ambient levels of carbonyls. This is because, as discussed in detail elsewhere (51, 55), more stringent emission limits have been required for new vehicles starting with 1997 model years. Emission limits for these newer vehicles are substantially lower (by factors of 6, 4, and 2 for CO, HC, and NOx emissions, respectively) than those for pre-1997 model years. Most new LD vehicles sold in Brazil since 1997 have continuous correction of fuel injection to optimize the fuel/air ratio and are equipped with catalytic converters, which further reduce exhaust emissions. As newer LD vehicles replace older models, fleet-averaged emissions of carbonyls and of their precursors (HC and NOx) should decrease, leading to a decrease in ambient carbonyl concentrations. Comparison with Literature Data for Speciated Carbonyls. There is little information regarding ambient concentrations of carbonyls other than formaldehyde and acetaldehyde in Brazilian cities. Grosjean et al. (44) have measured ambient concentrations of 10 carbonyls at several locations in Sa˜o Paulo (in 1986 and 1988) and Salvador (in 1988). The carbonyls identified were formaldehyde, acetaldehyde, acrolein, acetone, propanal, C4 unsaturated aliphatics (methacrolein and/or crotonaldehyde and/or methyl vinyl ketone), n-butanal + 2-butanone, benzaldehyde, C5 saturated aliphatic isomers (n-pentanal and/or isopentanal and/or 2and 3-pentanone), glyoxal, tolualdehydes, and methylglyoxal. No recent data are available from Sa˜o Paulo or Salvador for comparison. In Rio de Janeiro, Grosjean et al. (44) only reported the four carbonyls formaldehyde, acetaldehyde, acetone, and propanal in ambient samples collected in 1987 at one location and in one highway tunnel. The acetaldehyde/ formaldehyde concentration ratio (ppb/ppb) averaged 1.15 for the ambient samples versus 0.66 in the present study. The acetone/formaldehyde concentration ratio (ppb/ppb) averaged 0.24 for the ambient samples versus 0.20 in the present study. Reactivity Considerations. Once emitted into ambient air, carbonyls undergo photochemical reactions that lead to free radicals, other carbonyls, peroxyacyl nitrates, and ozone. Using the measured ambient concentrations of carbonyls in Rio de Janeiro, it is possible to calculate their relative importance with respect to ozone formation. To do this, we calculate the product of the carbonyl concentration and its maximum incremental reactivity (MIR) coefficient (57, 58). Concentrations of carbonyls varied from one day to the next (see Table 1), and as a result the relative importance of carbonyls with respect to ozone formation also varied from one day to the next. Nevertheless, it is useful to calculate 1394
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TABLE 5. Ozone Formation Ranking of Rio de Janeiro Ambient Carbonyls carbonyla formaldehyde acetaldehyde methylglyoxal propanal acrolein glyoxal butanal and/or isobutanald crotonaldehyde C6 aliphatic isomer 1b 2-butanone (MEK) acetone pentanal isopentanal hexanal methacrolein 2-pentanone C6 aliphatic isomer 2b C5 aliphatic isomerb 4-methyl-2-pentanone (MIBK) dimethylbenzaldehydese tolualdehydesf benzaldehyde % contribution of each functional group saturated aliphatic aldehydes aliphatic dicarbonyls unsaturated aliphatic carbonyls saturated aliphatic ketonesg aromatic carbonyls
product of MIR coeffb and av concnc
% of total
97.2 71.4 16.9 8.3 6.2 5.1 3.2 3.0 2.5 2.1 1.8 1.6 1.5 1.4 0.9 0.7 0.5 0.3 0.2 -0.1 -0.3 -0.7
43 32 7.6 3.7 2.8 2.3 1.5 1.4 1.1 0.94 0.80 0.70 0.66 0.61 0.40 0.32 0.22 0.12 0.07 -0.04 -0.12 -0.29
82.5 9.83 4.54 3.56 -0.46
a Listed in order of decreasing contribution. Omitted are anisaldehyde, acetophenone, indanone, and trans-cinnamaldehyde, which were present at very low concentrations (see Table 1) and for which MIR coefficients are not available. b MIR, maximum incremental reactivity coefficient (units: grams of ozone formed per gram of carbonyl). MIR coefficients are from Carter (58) except for the dimethylbenzaldehydes, estimated MIR ) -0.48, see text. The C5 isomer and the two C6 isomers were arbitrarily assigned the MIR coefficients of ketones, i.e., 3.07 and 3.55, respectively (58). The contribution of these compounds is underestimated if they are aldehydes, for which the MIR coefficients are higher (5.76 and 4.98, respectively; 58). c From Table 1; units: micrograms per cubic meter. d Using the MIR coefficient of butanal, 6.13; that for isobutanal is slightly lower, 5.87 (58). e Sum of the four isomers listed in Table 1. f Sum of ortho, meta, and para isomers. g Including the C5 isomer and the two C6 isomers, see footnote b.
ozone formation from carbonyls using the average concentrations given in Table 1 and the most recent MIR coefficients of Carter (57). We omitted anisaldehyde, acetophenone, trans-cinnamaldehyde, and indanone, which were present at very low ambient concentrations and for which MIR coefficients are not available. We assumed that the C5 (one isomer) and C6 (two isomers) saturated aliphatics were ketones and used the corresponding MIR coefficients. We assigned an MIR coefficient of -0.48 to the four dimethylbenzaldehyde isomers. This value was estimated from Carter’s MIR coefficients for benzaldehyde (-0.61) and for tolualdehydes (-0.54) and by taking molecular weight differences into account. The results are given in Table 5. On average, ozone formation from ambient carbonyls in Rio de Janeiro is dominated by formaldehyde (43% of total) and acetaldehyde (32% of total) followed by methylglyoxal (8% of total), propanal (4%), acrolein (3%), and glyoxal (2%). Saturated aliphatic aldehydes account for 82.5% of the total, followed by aliphatic dicarbonyls (9.8%), unsaturated aliphatic aldehydes (4.5%), saturated aliphatic ketones (3.6%), and aromatic carbonyls (-0.5%). We also ranked ambient carbonyls in Rio de Janeiro for their importance with respect to reaction with the hydroxyl radical (OH). These calculations, not shown, were carried out by multiplying the carbonyl concentration (units of ppb) by the numerical value of the carbonyl-OH reaction rate
constant (59). The most important carbonyl with respect to reaction with OH was acetaldehyde, closely followed by formaldehyde. The aromatic carbonyls, which made only a small negative contribution to ozone formation, were as a group more important with respect to reaction with OH. The photochemical oxidation of aromatic aldehydes leads to peroxybenzoyl nitrates (60, 61), which have received attention as severe eye irritants (60) and as mutagens (62).
Acknowledgments This work has been sponsored by Petro´leo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, Brazil, Contract CENPES650.2099001. We thank Alzira S. A. G. da Silva, Jose´ A. A. Rodrigues, and Luiz H. Heckmaier of FEEMA for permission to collect our samples at the FEEMA monitoring station in downtown Rio de Janeiro and for making available air quality and meteorological data. D.G. also thanks Roberto Godinho, Claudio D. Alonso, and Maria Helena R. B. Martins of CETESB, who over the years have made available several unpublished reports on ambient carbonyls in Sa˜o Paulo.
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Received for review July 10, 2001. Revised manuscript received December 19, 2001. Accepted December 20, 2001. ES0111232 VOL. 36, NO. 7, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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