Environ. Sci. Techno/. 1994, 28, 146-152

Characteristics of Aldehydes: Concentrations, Sources, and Exposures for Indoor and Outdoor Residential Microenvironments

Junfeng Zhang

Joint Graduate Program in Exposure Assessment, Department of Environmental Sciences, Rutgers University and UMDNJ-Robert Wood Johnson Medical School, 68 1 Frelinghuysen Road, Piscataway, New Jersey 08855-1 179

Qingci He+

Wuhan Environmental Protection Research Institute, Wuhan City, People‘s Republic of China

Paul J. Lloy’

Environmental and Occupational Health Sciences Institute, UMDNJ-Robert Wood Johnson Medical School and Rutgers University, 68 1 Frelinghuysen Road, Piscataway, New Jersey 08855-1 179

Simultaneous indoor and outdoor measurements of al- dehydes were made at 6 residential houses located in a suburban New Jersey area during the summer of 1992. Each house was measured for six days and controlled for ventilation and gas combustion conditions during the study. Formaldehyde, acetaldehyde, and seven other aldehydes were identified in the residential air. The study presents the first measurements of nine aldehyde species in both indoor and outdoor air. The total concentrations of the nine aldehydes were 19.12 f 10.88 ppb outdoors and 62.57 f 21.75 ppb indoors. Formaldehyde was the most abundant aldehyde. Except for propionaldehyde, the indoor concentrations were found higher than the outdoor concentrations for all the other compounds, indicating the presence of significant indoor sources such as direct emissions and indoor chemical formation. Ozone concentrations were measured simultaneously during the study, and it was observed that several aldehydes can be generated through indoor ozone chemistry. The study provided evidence to support laboratory results obtained by other investigators that predicted aldehyde generation through indoor ozone chemistry. The residential expo- sures to formaldehyde and total aldehydes were assessed based upon some assumptions, and the outdoor exposures were negligible compared to the indoor exposures.

Introduction

Aldehydes are of great concern because of their adverse health effects. For example, formaldehyde and acrolein are well known for their irritation effects on animals and humans ( I ) , and formaldehyde has been regulated for its carcinogenic properties (2). Aldehydes in the atmosphere have also received attention because of their influence on photochemical smog processes. Various aldehydes in polluted ambient air are produced directly by the com- bustion of hydrocarbon fuels and indirectly by the atmospheric oxidation of the same fuels (3,4). Natural sources may generate certain amounts of aldehydes through direct emissions (e.g., biogenic emissions of formaldehyde) and through photochemical oxidation of naturally emitted hydrocarbon precursors (e.g., isoprene emitted from natural sources) (5-7). Ambient measure- ments have been made in polluted urban air during

* Author to whom correspondence should be addressed. t Visiting Scientist at EOHSI.

146 Environ. Sci. Technoi., Vol. 28, No. 1, 1994

photochemical episodes (8-11) and in “clean” rural air (5, 12). Thanks to the development of the analytical tech- niques, the number of aldehyde species identified and measured has increased. Using a sensitive method, nine aldehyde compounds were detected in our measurements conducted in a residential area in suburban New Jersey during June-August of 1992. Characteristics of the aldehydes in the ambient outdoor air, such as concentration patterns, exposures, and the relationships with tropo- spheric ozone, were investigated in the study.

Indoor air pollution has been recognized to be very important because individuals spend large fractions of their time in indoor environments. For those compounds having indoor sources, the indoor exposures can be high. Form- aldehyde is well known to have its indoor sources, e.g., direct emissions from wood products, and it has been measured in office buildings (13) and residential houses (14,15). However, few measurements of other aldehydes have been reported indoors (16) and indoor aldehyde characteristics such as concentrations, sources, and ex- posures are poorly understood. Our study completed aldehyde measurements in six residential houses in the suburban New Jersey area and simultaneously measured the concentrations of the same aldehydes outdoors. Indoor ozone was also monitored simultaneously in an attempt to identify plausible correlations between ozone and aldehydes indoors. The six houses, each with central air conditioning and a gas stove, were controlled for ventilation and gas combustion conditions during the study to test the impacts of each on the indoor aldehyde levels. In addition, the average indoor exposures to formaldehyde and the total aldehyde were assessed using common exposure factors for inhalation rate and exposure duration in the residential microenvironments.

Experimental Methods. Thirty-six afternoons (=2:00 to 8:OO p.m.) from June 21 to August 5,1992, were chosen for sample collection. Indoor and outdoor mea- surements of aldehydes and ozone were made at six residential houses located in a suburban area in Central New Jersey. The houses were carpeted, had central air- conditioning, and were occupied by nonsmokers. A natual gas stove and oven were installed in each kitchen. All stoves had pilot lights. In order to test the hypothesis that aldehydes indoors may come from outdoors through infiltration and may be emitted directly from gas com- bustion indoors, each house was controlled for ventilation and indoor combustion conditions during the study. The study had block factorial statistical design with two fixed

0013-936X/94/0928-0146$04.50/0 0 1993 American Chemlcal Society

factors (Le., ventilation condition and gas combustion condition) and one block factor (Le., house). The treatment of the block factor was to reduce the experimental variations from the house differences when testing the other fixed factors (1 7). The ventilation conditions included central air conditioner (AC) on (window closed), window open (AC off), and window closed (AC off). A specific ventilation condition was used throughout a sampling day (=8:00 a.m. to 8:OO p.m.), and the samples were collected only in the afternoon. The combustion conditions included gas-on and gas-off. Gas-on that the gas stove and/or oven were turned on for a t least 1 h during sampling. Gas-off means that all gas combustion sources were absent during sampling. All indoor samples were collected in the kitchens, and all outdoor measurements were made in the backyards.

Aldehyde Measurements. The sampling medium was a Sep-Pak c18 cartridge (Waters, Millipore Corp.) coated in situ with a solution of 2,4-dinitrophenylhydrazine (DNPH). DNPH was purified by multiple recrystalliza- tion in HPLC grade acetonitrile (ACN) and washed by methylene chloride, cyclohexane, and ACN (all HPLC grade), respectively. Batches of the cartridges were prepared based upon the procedures developed by other investigators (18-20). Each cartridge was washed with 2 mL of ACN, 2 mL of water (HPLC grade), and 2 mL of ACN again and then coated by slowly passing 5 mL of the freshly-made coating solution, which contained 20 mL DNPH-ACN-saturated solution and 1 mL concentrated HClacid in lo00 mL ACN, through the cartridge by gravity. Batches of coated cartridges were dried by passing zero- grade nitrogen gas through for 15-20 min a t a flow rate of 200-300 mL/min. Each dried cartridge, which contains about 1 mg of DNPH, was sealed with Teflon tape, wrapped in aluminum foil, and stored in a plastic vial a t refrigerator temperature before use. The cartridge was reported to be good for a t least 6 months when stored under refrigerator temperature (18,21). The storage time of our cartridges was less than 80 days.

Aldehyde samples were collected by removing the Teflon tape and connecting the downstream end of the cartridge to a flow meter and a sampling pump. The flow meter was calibrated before and after sampling. The sampling pump was a Medo vacuum pump (Model Vp 0125), which was modified to provide an adjustable flow rate. It was suitable for indoor sampling because of its low noise level. The samples were typically collected for 2.5-3.5 h (between 3:30and 7:Wp.m. each day) a t a flow rate of 0.5-1.0 L/min. After sampling, each cartridge was resealed with Teflon tape, wrapped in aluminum foil, and stored in a vial a t low temperature again.

The sampled cartridge was eluted slowly with 4 mL of ACN, and a 20-pL aliquot was injected into the HPLC system through an autosampler. The HPLC system employed was Spectra-Physics Instrument Model 8800. The analytical conditions were as follows: Nova-Pak Cp3 analytical column (3.9 X 150 mm) and its guard column (Waters); gradient mobile phase, A = water/ACN/tet- rahydrofuran 60/30/10 v/v/v, B = water/ACN 40160 v/v, 100% A for 1 min, then linear gradient from 100% A to 100% B in 10 min, and then 100% B for another 10 min; mobile-phase flow rate: 1.5 mL/min; detector, UV at 360 nm. Each individual aldehyde was identified by matching its retention time with the retention time of the freshly synthesized DNPH-aldehyde derivative (hydrazone) un-

der the same chromatographic conditions. The hydrazone was also used as an external standard for quantitative analysis based on the known stoichiometry of the reaction. The detailed synthesis method of hydrazones can be found in some previous works (18,22). Calibration curves were constructed with analyte concentrations (as aldehyde) in the range 0.050-1.00 pg/mL (5-10 data points) and yielded linear plots with near-zero intercepts. The linear regres- sion coefficients had R2 > 0.99 for all identified aldehydes.

The DNPH cartridge collection efficiency, as measured by using two cartridges in series and calculated as the percentage of the amount collected onto the upstream cartridge in the total amount collected onto the both cartridges, was above 93 % for all aldehydes. The recovery rate was also measured in the laboratory by using a glass evaporation box. Based upon the amount of an aldehyde injected into the box and the amount collected onto the cartridge, the recovery was >90 % . The method repro- ducibility, as measured by using nine pairs of parallel or side-by-side samples, was found typically within 20% RSD. The analytical detection limit was quite low (e.g., 0.1 ng for formaldehyde-DNPH derivative). Depending upon the aldehyde species and the sampling volume, the concentration detection limits in the air ranged from 0.1 to 0.4 ppb.

Ozone Measurements. Ozone concentrations were measured with a portable ozone analyzer (Thermo En- vironmental Instruments, Inc., Model 560), which is based on the vapor-phase chemiluminescent reaction of ozone and ethylene. The chemiluminescent ozone analyzer (rather than UV photometric ozone analyzer) was chosen because of its specificity for ozone, eliminating the possible interference from other compounds which may be found in indoor and outdoor air. The ranges used were 0-0.1 and 0-1.0 ppm; sensitivity is 1 ppb; response time is less than 20 s; and noise is less than 0.7 ppb. The air was sampled at a rate of approximately 1 L/min using Teflon tubing. The analyzer was calibrated by primary standard methods before use and calibrated weekly by a calibrated portable ozone generator (Thermo Environmental Model 165). A chart recorder (Cole Palmer Model 8376-30) was used for the continuous recording of ozone concentration data. The analyzer was switched between outdoor and indoor sampling every 30 min during the sampling period. A 20-m long Tygon tubing was used to take the exhaust gas from the analyzer out of the sampling sites, because unreacted ethylene was contained in the exhaust gas and could interfere with the measurements of ozone and other compounds.

Results and Discussion

Nine aldehydes were measured outdoors and indoors. They included formaldehyde (CI), acetaldehyde (CZ), propionaldehyde (C& 2-furaldehyde (2-fur), butyralde- hyde (C4, benzaldehyde (benz), isovaleraldehyde (iso-Cg), n-valeraldehyde (n-C3, and n-hexaldehyde (n-Cs). The concentrations of these carbonyls in the outdoor air and indoor air are summarized in Table 1. In order to perform statistical analyses of the data, an undetected compound was assumed to have a concentration of half of its detection limit. Samples were collected in the afternoon which is when photochemical smog products accumulate in the atmosphere. The aldehydes have a typical diurnal smog cycle: peak concentrations occurring in the afternoon (5,

Envlron. Sci. Technol., Vol. 28. No. 1, 1994 147

Table 1. Indoor and Outdoor Concentrations of Aldehydes.

no. of no. of compound samples (N) detected (n) n/N ( % I mean (ppb) SD (ppb) 75% tile (ppb) min (ppb) mas (ppb)

formaldehyde outdoor 36 36 100 12.53 9.43 20.37 2.02 34.05 indoor 36 36 100 54.56 19.89 61.24 26.88 101.70

acetaldehyde outdoor 36 36 100 2.64 2.32 2.55 0.99 12.66 indoor 36 36 100 2.95 2.68 3.31 0.65 16.08

indoor 36 34 94 1.15 0.92 1.43 0.10* 5.64 P-furaldehyde outdoor 36 7 19 0.17 0.17 0.15 0.06* 0.69

indoor 36 19 53 0.27 0.27 0.39 0.07. 1.50 butyraldehyde outdoor 36 25 69 0.50 0.36 0.73 0.08* 1.23

indoor 36 28 78 0.66 0.55 0.98 0.05* 2.38 benzaldehyde outdoor 36 14 39 0.25 0.25 0.43 0.05* 0.89

indoor 36 22 61 0.38 0.30 0.52 0.05* 1.33 isovaleraldehyde outdoor 36 23 64 0.37 0.35 0.48 0.05* 1.63

n-valeraldehyde outdoor 36 34 94 0.80 0.38 0.91 0.07* 1.74

n-hexaldehyde outdoor 36 35 97 0.60 0.32 0.63 0.05* 1.88

total outdoor 36 36 100 19.12 10.88 28.08 6.39 43.96 indoor 36 36 100 62.57 21.75 76.19 35.41 114.15

propionaldehyde outdoor 36 35 97 1.27 0.40 1.51 0.08* 2.00

indoor 36 28 78 0.41 0.31 0.47 0.05* 1.20

indoor 36 36 100 0.91 0.49 1.01 0.28 2.02

indoor 36 36 100 1.28 0.80 1.42 0.54 3.99

An asterisk (*) = 1/2 of detection limit.

-B- 03/10 -Formaldehyde 35 r

1 I I I I I 1 I I I I L

0 3 6 9 12 15 18 21 24 27 30 33 36

sampling day Figure 1. Outdoor formaldehyde and ozone concentratlons.

12), the outdoor concentrations of the aldehydes reported in Table 1 can be considered as the peak concentrations for a day. Formaldehyde and acetaldehyde were found in all the indoor and outdoor samples; propionaldehyde, n-valeraldehyde, and n-hexaldehyde were relatively abun- dant; butyraldehyde, isovaleraldehyde and benzaldehyde were less abundant; and 2-furaldehyde was the least abundant among the identified aldehydes. The total concentration of the nine aldehydes had a mean outdoor level of 19.12 f 10.88 ppb, and formaldehyde accounted for 60 f 15% and acetaldehyde for 15 f 10%. The nine aldehydes had a mean indoor level of 62.57 f 21.75 ppb, and the most abundant species was formaldehyde, ac- counting for 87 f 6%. A wide range of the aldehyde concentrations was observed both outdoors and indoors over the 36-day sampling period.

Characteristics of Outdoor Aldehydes. Among the aldehydes identified in outdoor air, the straight-chain compounds (i.e., C1, CZ, C3, n-C5, n-Cs) were relatively more abundant than the aromatic aldehyde (benzalde-

hyde) and the branch-chain aldehyde (iso-CS). Although the CS aldehyde acrolein can be resolved from other carbonyls (even acetone) by the analytical method, it was not found in the collected samples. During the summer- time, aldehydes in polluted air are mainly generated from complicated atmospheric oxidation of hydrocarbons (HC) by various free radicals which are formed through pho- tochemical reactions (23), although they may also come from direct emissions of incomplete fuel combustion. This can be inferred by the relationship between aldehydes and tropospheric ozone. For example, similar concen- tration patterns were observed for outdoor ozone and formaldehyde (see Figure 1, where ozone concentrations were normalized by a factor of 10 to match the formal- dehyde concentration scale). A significant correlation (see Figure 2) between these two compounds was found at a level of a = 0.05 (sample number N = 36, Spearman r = 0.503).

As indicated in Table 2, the ratio of formaldehyde concentration to acetaldehyde concentration (Cl/C2) was

148 Envlron. Scl. Technol., Vol. 28, No. I, 1984

Table 3. 1/0 Ratios of Aldehydes in Residential Air

compound mean SD 75% tile min max

m m m

2 0 -

I I 1 I 50 100 150 200

Ozone (ppb) Flguro 2. Correlatlon between outdoor formaldehyde and outdoor ozone; the llne Is In the llnear regression curve, r = 0.50, N = 38.

Table 2. Aldehyde Concentration Ratios (C& and Ca/Cs)

rato N mean SD min max range

CiIC2 36 5.8 4.9 1.1 22.0 20.9 CdCs 36 2.3 2.1 0.8 10.4 9.6

about 6. It was reported that a typical CdC2 ratio is about 1-2 for an urban area and about 10 for a deciduous forested area. Compared to the typical C1/C2 ratios of about 2 in Southern California sites (8,24) and 3-4 in Central Ontario sites (5), the C1/C2 ratio in our suburban residential sites was higher. The high C1/C2 observed in our study may suggest that direct emissions of formaldehyde were more important in the suburban New Jersey area. On the other hand, it may reflect the local participation of natural reactive hydrocarbons, such as isoprene, whose oxidation can yield more formaldehyde than acetaldehyde. Isoprene is a major reactive hydrocarbon that can yield a C1/C2 ratio of 10 (25) and is mainly a biogenic emission. The samples were collected in the backyard, and each was surrounded by trees and grass. Thus, isoprene may play a role in generating formaldehyde.

Propionaldehyde $3) is believed to be associated only with anthropogenic hydrocarbon precursors, in contrast, other carbonyl compounds have both anthropogenic and natural hydrocarbon precursors (5). Therefore the ratio of acetaldehyde to propionaldehyde concentrations (C2/ CS) is often used as an effective indicator of the presence of anthropogenic pollution. In the “clean” background area, the propionaldehyde level is very low while acetal- dehyde can have a baseline level because naturally emitted hydrocarbons form acetaldehyde via atmospheric photo- chemical reactions but do not form propionaldehyde. Thus CdC3 ratio would be high in rural and remote atmospheres. For example, c2/c3 was reported to be 21 a t a rural site (5). In polluted urban air, hydrocarbons mainly come from fossil fuel combustion sources such as the automobile. The hydrocarbons emitted from these sources can form both acetaldehyde and propionaldehyde via atmospheric chem- istry and yield a much smaller c2/c3 ratio, for example, -1 in an urban area (8). Our measurements found that

formaldehyde acetaldehyde propionaldehyde 2-furaldehyde butyraldehyde benzaldehyde isovaleraldehyde n-valeraldehyde n-hexaldehyde total

7.20 5.93 9.88 1.25 30.10 1.38 0.91 1.62 0.12 4.53 0.99 0.78 1.31 0.07 4.66 2.58 2.99 3.98 0.08 16.67 2.97 5.07 2.43 0.10 24.88 3.47 4.07 6.31 0.09 19-00 2.47 3.09 3.85 0.06 14.88 1.94 3.86 1.42 0.40 22.63 2.57 2.80 2.63 0.88 18.20 4.26 2.56 5.52 1.00 11.28

the C2/C3 ratio was -2, indicating the presence of hydrocarbon precursors from anthropogenic sources in the suburban New Jersey area.

Sources of Indoor Aldehydes. Comparison of the indoor and outdoor aldehyde concentrations found “indoor > outdoor” for almost every measurement pair. The relationship between indoor and outdoor aldehyde con- centrations is illustrated in Table 3 by the ratios of the indoor/outdoor aldehyde concentrations (I/O ratios). I t is seen that with the exception of propionaldehyde (I/O = 0.99 f 0.78), all the other identified aldehydes had mean 1/0 > 1. The higher indoor aldehyde concentrations may result from the complex chemical and physical processes which determine the generation, accumulation, and re- moval of the aldehydes in the indoor environments. A specific aldehyde present in the indoor air may have its own special sources, although it can share some common sources with other aldehyde species.

Direct Emissions f rom Indoor Sources. The direct emissions within the indoor environment could be the dominant source for some aldehyde species. Formalde- hyde is a famous example, as it is well known that direct emissions from construction materials (e.g., wood product such as particle board) and furniture can generate a significant indoor formaldehyde levels (15). Our results clearly demonstrated that formaldehyde concentrations were much higher in indoor air (54.56 ppb) than in outdoor air (12.53 ppb) for the residential environments (see Table 1). The mean I/O ratio for formaldehyde was as high as 7.20 f 5.93 (see Table 3). Furthermore, the indoor formaldehyde concentrations found in the six studied houses, shown in Figure 3, indicates that the highest aldehyde concentration was found in house 2. This house was only 9-months-old when the samples were taken, and the remaining houses were built between 10 and 40 years ago. The high formaldehyde concentrations in house 2 probably reflect the high formaldehyde emission rate from a new house. The second example is acetaldehyde. Since acetaldehyde is a product of the human metabolism and present in human expired air (261, the higher acetaldehyde concentrations indoors (than outdoors) may be related to direct emissions from humans. At least two persons were inside the houses when the samples were collected. However, it was hard to obtain a quantitative correlation between the indoor acetaldehyde level and the occupancy due to the limitation of the study design. Another example is 2-furaldehyde. The data in Table 1 show that 2-fural- dehyde was detected in only 19 ’?6 of the outdoor samples while it was found in 53 9% of the indoor samples. Indoor 2-furaldehyde may be related to emissions from cooking practices (e.g., it is known that 2-furaldehyde can be extracted from hulls of rice, grain, and other cereal),

Envlron. Sci. Technol., Vol. 28, No. 1, 1994 149

n P

v

H e 3 a" 8 su

5 0 -

"'[ 1

1001

0 Q *

01 I I I I I I

1 2 3 4 5 6

House Flgure 3. Indoor formaldehyde concentrations in each sampled house: from the bottom to the top, the box lines in the figure represent loth, 25th, 75th, and 90th percentile, respectlveiy. ' and 0 represent outliners.

l 5 O I 100

5 0

0 1 I I

off on

Gas combustion Figure 4. Indoor formaldehyde concentrations vs Indoor combustion conditions: bottom to the top, the box lines in the figure represent loth, 25th, 75th, and 90th percentile, respecthrely. off = gas combustion off, on = gas combustion on.

It is known that incomplete combustion of fossil fuel can produce aldehydes and that the direct emission from automobile exhaustion is a source of atmospheric alde- hydes. However, no significant difference was found between the mean formaldehyde concentration when gas combustion was on and when gas combustion was off (see Figure 4) according to the analysis of variance (ANOVA): error term degree of freedom (DF) = 25, F = 0.38, and P value = 0.545 >> 0.05. For the other aldehydes, A N O V A also indicates that the mean aldehyde concentrations under different combustion conditions were not significantly different. Therefore, the impacts of gas combustion on indoor aldehyde concentrations were of no importance for the studied houses during the summertime. Two reasons may explain the insignificant contribution of gas

combustion to indoor aldehyde concentrations. One is that indoor gas combustion generates negligible amount of aldehydes, or that residential indoor air has other sources.

Outdoor Infiltration. There is always a possibility for the penetration of a pollutant present in the outdoor air into the houses. The outdoor infiltration source is particularly important for the pollutants which have no indoor sources. However, differences among the mean concentrations of each aldehyde for the three ventilation levels were not found to be significant according to A N O V A at a = 0.05. As an example, A N O V A results for formal- dehyde were F = 2.08, DF = 25, and P = 0.146 > 0.05. Therefore infiltration of the outdoor aldehydes to indoors was of minor importance.

Indoor Chemical Formation. Through their laboratory simulation study, Weschler et al. (27) reported that indoor ozone chemistry can play a role in generating indoor aldehydes. Volatile organic compounds (VOCs) and several aldehydes were measured in their freshly carpeted stainless-steel room in both the absence and presence of ozone, and it was observed that the gas-phase concen- trations of the selected VOCs significantly decreased in the presence of ozone and, conversely, the concentrations of aldehyde compounds (e.g., formaldehyde, acetaldehyde, and aldehydes with between 5 and 10carbons) significantly increased. The selected VOCs were compounds emitted from house carpets. The dark reaction of ozone with VOCs having unsaturated carbon-carbon (C=C) bonds was considered to be mainly responsible for the aldehyde generation. In these residential houses, indoor ozone was found at concentrations that ranged from 2 to 108 ppb with the highest frequency occurring between 30 and 60 ppb (28), indoor VOCs could be emitted from carpets and/ or other sources. Therefore, based upon the laboratory study (27), the indoor chemical formation of aldehydes could occur.

Using the mean ozone concentrations measured over the same time interval as when aldehyde sampling was conducted (28), the following aldehydes were found to be significantly correlated to ozone at a significance level of a = 0.05 (by Spearman correlation analysis): acetaldehyde (Cz), n-valeraldehyde (n-Cb), and valeraldehyde (C5 = iso- C5 + n-C5). The Spearman correlation coefficients ( r ) were 0.35, 0.42, and 0.48, respectively. The above-mentioned compounds were all observed to be generated by ozone reactions in the laboratory study of Weschler et al. (27). Therefore the evidence for indoor ozone chemistry as a potential source of certain aldehydes was observed in our field study. Formaldehyde had a significant formation via ozone chemistry in the laboratory but was poorly correlated with indoor ozone concentrations in the field study. This is not surprising because formaldehyde in the homes had much stronger direct emission sources.

Residential Exposures to Aldehydes. I t is exposure that determines the potential for deriving a biologically effective dose of a pollutant that can cause human health effects rather than the concentrations alone. The concept of exposure is well established; and models can be used to predict individual exposures which are based on the premise that the summation of pollutant values in all microenvironments (e.g., home, office, outdoors, in-tran- sit), weighted by the fraction of time spent in each microenvironment, provides an approximation of the integrated individual exposures (29,30). Mathematically,

150 Envlron. Scl. Technol., Vol. 28, No. 1, 1994

Table 4. Exposure Factors and Aldehyde Daily Exposures from Outdoor Residences

formaldehyde mean lower upper

C (ppb) 12.53 3.10 21.96 C (pg/ms) 15.54 3.84 27.23 CR (ma/h) 1.4 1.25 3 T (h/day) 0.44 0.3 0.6 PD (pg/day) 9.6 1.4 49.0

a Maea as formaldehyde.

total aldehyde4 mean lower upper

19.12 8.24 30.00 23.71 10.22 37.20 1.4 1.25 3 0.44 0.3 0.6

14.6 3.8 67.0

Table 5. Exposure Factors and Aldehyde Daily Exposures from Indoor Residences

formaldehyde total aldehyde4 mean lower upper mean lower upper

C (ppb) 54.56 34.67 74.45 62.57 40.82 84.32 C (pg/ma) 67.65 42.99 92.32 77.59 50.62 104.56 CR (m3/h) 0.83 0.63 1.25 0.83 0.63 1.25 T(h/day) 15.37 13.97 16.57 15.37 13.97 16.57 PD(pg/day) 863 378 1912 990 445 2166

a Mass as formaldehyde.

the average exposure, expressed as a potential dose (PD), for individual i in microenvironment j can be calculated from the following equation

PDij = Cj(CR)i,Tij

where Cis the concentration of the pollutant, CR is contact rate, and T is exposure duration.

In the study, the aldehyde concentrations (C) were associated with two microenvironments (j = indoors and outdoors). Since the aldehydes are gaseous species, the exposure route of concern is inhalation, and the contact rate (CR) is the inhalation rate of air (air volumeltime). Contact rate (CR) and duration (7‘) for residential indoor and outdoor microenvironments were estimated for an “average” person i based upon the EPA Exposure Factor Handbook (31). These are listed in Tables 4 and 5. Time (7‘) outdoors was assumed to be twice the yearly average, because people usually spend more time outdoors in the summer than in the winter. Using these assumptions, the average formaldehyde and total aldehyde exposures (as daily PD) in these residential microenvironments (j = outdoor and indoor) were estimated (Tables 4 and 5). The average PDs for outdoor formaldehyde and total aldehyde were estimated to be 9.6 and 14.6 pglday, respectively. These were negligible compared to the average PDs from the indoor residences, 863 for formaldehyde and 990 pg/ day for total aldehyde. Further, total PD (indoor + outdoor) of total aldehyde was about 1 mglday, and formaldehyde accounted for about 87% of the total aldehyde exposure.

Conclusions

Formaldehyde, acetaldehyde, propionaldehyde, butyr- aldehyde, isovaleraldehyde, n-valeraldehyde, n-hexalde- hyde, benzaldehyde, and 2-furaldehyde were identified in six residential houses in a suburban New Jersey area during the summer of 1992. Among these compounds, formal- dehyde was the most abundant aldehyde, accounting for 60 f 15 % of the total concentration of the nine aldehydes in the outdoor air (19 f 10.88 ppb) and 87 f 6% of the total indoor aldehyde concentration of 62.75 f 21.75 ppb.

Daily variations in outdoor aldehyde concentrations were observed to have patterns similar to variations in tropospheric ozone concentrations, which is typical for secondary products found in photochemical smog. The formaldehydelacetaldehyde ratio was -6, while acetal- dehyde/propionaldehyde ratio was -2.

Indoor aldehyde concentrations were found to be higher than outdoor aldehyde concentrations. Indoor ozone chemistry was believed to play a role in generating several of the measured aldehydes: acetaldehyde, n-valeralde- hyde, and valeraldehyde (iso- plus n- valeraldehyde). The correlations between indoor ozone and aldehydes support the results of the laboratory study by Weschler et al. (27), which found these aldehyde compounds can be produced through the reactions of indoor ozone with certain VOCs emitted from house carpets. Significant impacts of indoor gas combustion and ventilation conditions on the indoor aldehyde levels were not found through statistical tests. An “average” person’s exposures to formaldehyde and total aldehydes in the residential air, expressed as mean potential dose, were estimated to be 873 and 1005 pglday, respectively. The outdoor exposures were deminimus compared to indoor values.

Acknowledgments

We thank our six volunteer families for kindly providing their houses. We thank Dr. Clifford Weisel, EOHSI of Rutgers University and UMDNJ-Robert Wood Johnson Medical School, for useful discussions and help on instrumentation. We also thank Mr. Tom Wainman, EOHSI, for his help on the modification of sampling pumps. This work was supported in part by US. EPA Cooperative Agreement CR-818567-01-1. Dr. William E. Wilson is the project officer. This manuscript has not undergone the EPA internal review, and the conclusions reflect only the opinions of the authors. Dr. Lioy’s research was supported in part by the NIEHS Center Grant 05022.

Author Supplied Registry Numbers: Formaldehyde, 50-00-0; acetaldehyde, 75-07-0; propionaldehyde, 123-38- 6; butyraldehyde, 123-72-8; 2-furaldehyde, 98-01-1; val- eraldehyde, 110-62-3; hexaldehyde, 66-25-1; benzaldehyde, 100-52-7; acetonitrile, 75-05-8; DNPH, 119-26-6; methylene chloride, 75-09-2; cyclohexane, 110-82-7; hydrochloric acid, 7647-01-0; nitrogen, 7727-37-9; water, 7732-18-5; tetrahy- drofuran, 109-99-9; ozone, 10028-15-6.

Literature Cited

Amdur, M. 0. Air Pollutants. In Casarett and Doull’s Toxicology: The Basic Science of Poisons, 4th ed.;Amdur, M. O., Doull, J., Klaassen, C. D., Ed.; Pergamon Press: New York, 1991; Chapter 25, pp 866-868. National Research Council. Formaldehyde and other al- dehydes. Board on Toxicology and Environmental Health Hazards, National Academy Press: Washington, DC, 1981. Baugh, J.; Ray, W.; Black, F. Atmos. Enuiron. 1987, 21, 2077-2082. Calvert, J. G.; Madronich, S. J. Geophys. Res. 1987, 92, 2211-2220. Shepson, P. B.; Hastie, D. R.; Schiff, H. I.; Polizzi, M.; Bottenheim, J. W.; Anlauf, K.; Mackay, G. I.; Karecki, D. R. Atmos. Environ. 1991,25A, 2001-2015. Lloyd,A. C.;Atkinson,R.;Lurmann,F. W.;Nitta,B.Atmos. Enuiron. 1983,17, 1931-1950. Seinfeld, J. H. Atmospheric chemistry and physics of air pollution; Wiley-Interscience: New York, 1986. Grosjean, D. Environ. Sci. Technol. 1982, 16, 254-262.

Environ. Sci. Technol.. Vol. 28, No. 1, l9B4 151

(9) Grosjean, D.; Swanson, R.; Ellis, C. Sci. Total Environ. 1983, 29, 65-85.

(10) Kuwata, K.; Uebori, M.; Yamasaki, H.; Kuge, Y. Analyt. Chem. 1983,55, 2013-2016. Haszpra, L.; Szilagyi, I.; Demeter, A.; Turanyi, T.; Berces, T. Atmos. Environ. 1991,25A, 2103-2110. Schulam, P.; Newbold, R.; Hul1,L. A. Atmos. Environ. 1985, 19, 623.

(13) Bravo, H. A; Camacho, R. C.; Sosa, R. E.; Torres, R. J.; Torres, G. J. In Indoor Air ‘90, Proceedings of the 5th International Conference on Indoor Air Quality and Climate; Toronto, Canada, 1990; Vol. 2, pp 689-694.

(14) Liu, J.; Liu, Y.; Hu, H. In Indoor Air ‘90, Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Toronto, Canada, 1990; Vol. 2, pp 725-730.

(15) Muramatsu, S.; Matsumura, T.; Okamoto, S. In Indoor Air ‘90, Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Toronto, Canada, 1990;

(16) Lewis, C. W.; Zweidinger, R. B. Atmos. Environ. 1992,26A, Vol. 2, pp 561-564.

2179. (17) Hicks, C. R. Fundamental Concepts in the Design of

Experiments, 3rd ed.; Holt, Rinehart and Winston: New York, 1982.

Int. J. Environ. Anal. Chem. 1990, 38, 495-512. (18) Druzik, C. M.; Grosjean, D.; Van Neste, A.; Parmar, S. S.

(19) Tejada, S. B. Int. J. Environ. Anal. Chem. 1986,26, 167- 185.

(20) Grisjean, D. Environ. Sci. Technol. 1991,25, 710-715.

(21) Levin, J. 0.; Anderson, K.; Lindahl, R.; Nilsaon, C. A. Anal. Chem. 1985,57,1032-1035.

(22) Shriner, R. L.; Fuson, R. C., Curtin, D. Y.; Morrill, T. C. Systematic Identification of Organic Compounds, 6th ed.; John Wiley & Sons: New York, 1980.

(23) Finlayson-Pitta, B. J.; Pitta, J. N. Atmospheric Chemistry: Fundamentals and Experimental Techniques; John Wiley & Sons: New York, 1986.

(24) Singh, H. B.; Salas, L. J. Atmos. Environ. 1986,20, 1301- 1304.

(25) Jocob, D. J.; Wofsy, S. C. J. Geophys. Res. 1988,93,1477- 1486.

(26) Conkle, J. P.; Camp, B. J.; Welch, B. E. Arch. Environ. Health 1976, 30, 290-295.

(27) Weschler, C. J.; Hodgson, A. T.; Wooley, J. D. Environ. Sci. Technol. 1992,26,2371-2377.

(28) Zhang, J.; Lioy, P. J. Indoor Air, in press. (29) Sexton, K.; Spengler, J. D.;Treitman,R. D. Atmos. Environ.

(30) Lioy, P. J. Environ. Sci. Technol. 1990,24, 938-945. (31) U.S. EPA Exposure factors handbook; U.S. Government

Printing Office: Washington, DC, 1989;EPA/600/8-89/043.

1984,18,1385-1398.

Received for review May 27,1993. Revised manuscript received September 20, 1993. Accepted September 27, 1993..

@ Abstract published in Advance ACS Abstracts, November 1, 1993.

162 Environ. Scl. Technol., Vol. 28, No. 1, 1994