For the presentation at the Air and Waste Management Association’s 98th
Annual Meeting & Exhibition, June 21-24, Minneapolis, MN, USA
Measurement and Prediction of Indoor
Formaldehyde Concentration in Northeast China
Control # 1179
Yu-hua Li , Kun Wang , Qing-liang Zhao
School of Municipal & Environmental Engineering, Harbin Institute of Technology
202 Haihe Road, Nangang District, Harbin 150090, China
Chung-shin Yuan
Institute of Environmental Engineering, National Sun Yat-sen University, No.70,
Lian-hai Road, Kaohsiung City, Taiwan 80424, China
ABSTRACT
With the development of economy and the improvement of living condition,
decorating houses has been the hotspot of personal consumption in China for the past
two decades. Indoor formaldehyde pollution is ubiquitous in China, while it has
been mostly controlled in the developed countries. In this study, an investigation on
the measurement of indoor formaldehyde concentration in residential houses was
conducted in Harbin, located at the most chilly area in Northeast China. The results
showed that the concentration of indoor formaldehyde ranged from 0.017 to
1.302mg/m3, and only 22.8% of the residential houses met the formaldehyde standard
of 0.10 mg/m3 for National Air Quality Standard of China. The monthly average
formaldehyde concentration in summer (June-August) was about twice higher than
those in winter (November-March). A strong correlation between the monthly
average indoor formaldehyde concentration and the monthly average temperature
(R2=0.8652) was obtained. Furthermore, a mathematical model was successfully
developed to predict the concentration of indoor formaldehyde in Chinese residential
houses. Field measurements of indoor formaldehyde concentration in residential
houses were also conducted for various decoration time in order to investigate the
influence of decoration time on the indoor formaldehyde concentration.
INTRODUCTION
Indoor air pollution has become a serious problem in China for the past two decades,
since people could expose to indoor air pollutants, due to poor ventilation and the
existence of indoor air pollution sources.
Chemical substances could be
continuously and slowly released from the building materials, decorating materials,
and commodities, which have been widely applied in the residential houses. There
are many health symptoms appeared on people lived in contaminative rooms, such as
headache, respiratory tract infection, nausea, hypersusceptibility and dermatitis.1
People recognize that indoor air quality may be more important than outdoor air
quality because they spend over 80% of their time indoors.2-4 Recent studies in
1
different indoor environments such as office building, residential house, classroom,
shopping mall and restaurant that in group demonstrate that, in most cases, the
concentration of target air pollutants in indoor environments are higher than those in
outdoor environments.5-10 In particular, indoor formaldehyde which is potential to
cause cancer is ubiquitous in China, owing to the widely use of laminate board.11-13
The laminate board is one of the major sources that contribute to indoor formaldehyde
pollution. Better manufactural technique of laminate board is required in China,
which is especially important to improve indoor formaldehyde pollution.
Indoor air pollution resulted from the fitment has been paid more attention in recent
years in China. At present, the regulation is not completely established since indoor
air pollution has not been thoroughly investigated. As a result, the indoor air
pollution was serious increasingly.
Actually, the investigation of indoor
formaldehyde pollution has been conducted abroad and home. Their results show
that the formaldehyde pollution widely exists in indoor environments all over the
world, which has been paid much attention in many countries since 1980s. 14 Many
investigations on indoor formaldehyde pollution have been conducted in America,
Europe and Japan, which has been mostly controlled in the developed countries. 15-19
The results obtained from several cities in China showed that the maximal value of
indoor formaldehyde concentration in newly decorating rooms was higher than 2.300
mg/m3 with an average of 0.219 mg/m3.20 Approximately 70%~80% of them had to
remove the formaldehyde according to the National Air Quality Standard of China
(0.1 mg/m3). Simulate to these cities, indoor air pollution resulted from the fitment
may be more serious in Harbin, which located at the most chilly area in Northeast
China. Harbin is the capital of Heilongjiang Province, the northernmost province in
China. The space heating period in Harbin is about half a year long. The residents
seldom open windows in winter for the reasons of cold weather and energy
conservation. People lived in Harbin stay longer in indoors than those who lived in
other cities in China. Therefore, the indoor air pollution becomes more serious and
has higher influence on human health. The climate and life style have significant
influences on indoor air pollution. The residents lived in Harbin have right to know
the current status of indoor air quality. In addition, the city government needs those
data to establish regulations to maintain good indoor air quality. Thus, it is highly
required to provide the quantitative information of indoor formaldehyde pollution in
Harbin.
In this study, an investigation on the measurement of indoor formaldehyde
concentration in residential houses that have been decorated was conducted in Harbin
in 2003. A mathematical model was then developed based on the experimental data
to predict the concentration of indoor formaldehyde. Factors including temperature,
relative humidity, air exchange rate, the surface area of the board, the quality of the
board and furniture, and the space of the room were taken into consideration in the
model. Moreover, this study intended to know the duration of formaldehyde in
residential houses, which could last for a long time and was harmful to the residents.
2
Therefore, the indoor formaldehyde concentration in the residential houses that have
finished fitment for different duration was measured simultaneously.
EXPERIMENTAL METHODS
Site Selection
The investigation of indoor formaldehyde pollution was conducted in Harbin from
January to December in 2003. There are seven districts in Harbin, including
Nangang, Daoli, Daowai, Taiping, Xiangfang, Dongli, and Pingfang. A total of 246
samples were sampled in these districts during the investigation period as shown in
Figure 1. The sampling sites were selected randomly and their distribution fairly
reflected the residents’ living condition as well as the decoration status of the
residential houses in Harbin.
After investigating the level of indoor formaldehyde in metro Harbin, another fifty
decorated residential houses were further selected specially in Nangang district where
most of the residential houses were decorated. The decoration time of the fifty
residential houses ranged from one month to two years. Indoor formaldehyde
concentration was measured in the fifty residential houses in order to know the
duration of formaldehyde in the houses, which is very important for the exposure and
health risk assessment of indoor formaldehyde.
Sampling and Analysis
In this study, the sampling of indoor formaldehyde followed a standard procedure
reported in the control regulation of indoor air pollution and criterion of indoor air
quality in China.20 The windows and doors of the residential houses were closed for
approximately 12 hours till the sampling was completed. The distance between the
sampling point and the wall were longer than 0.5 m and the height of the sampling
point was 0.5~1.5 m above floor. Indoor temperature, relative humidity, and air
Figure 1. Indoor air samples collected at 7 districts of Harbin in 2003.
Taiping
5.28%
Dongli 8.94%
Pingfang 0.81%
Xiangfang 9.35%
Nangang
47.97%
Daowai 2.44%
Daoli
25.20%
3
pressure were simultaneously monitored during the sampling period. Factors
including the weather condition, the area of the room, the finishing time of the
building, and the decorating materials were also recorded. These factors are required
for further analysis of measured data.
In this study, the analysis of formaldehyde followed the Standard Hygienic Test
Methods for the Analysis of Atmospheric Formaldehyde in Residential Area, Method
(GB/T16129-1995)-AHMT. Indoor air was bubbled into distilled water in a flow
rate of 1.0 L/min for twenty minutes to collect formaldehyde. An indoor air quality
sampler manufactured by Electromechanical Equipment Company (Model KB-6A)
was used to sample indoor air. The gas flow rate was proofread with a soap bubble
flow meter to insure the accuracy of the sampler. An UV-visible spectrophotometer
manufactured by Rainbow Analysis Instrument (Model UV-752) was applied to
determine the concentration of formaldehyde.
RESULTS AND DISCUSSION
Analysis of Indoor Air Pollution Status
Formaldehyde was detected in the indoor environments of the 246 residential houses
in Harbin. The distribution of indoor formaldehyde concentration is shown in Table
1. The results of on-site measurements showed that the concentration of indoor
formaldehyde ranged from 0.017 to 1.302 mg/m3 with an average of 0.219 mg/m3.
The highest concentration of indoor formaldehyde was measured in June while the
lowest was in November. Results from the statistical analysis of detected data
showed that, at present, the formaldehyde pollution in indoor environments was quite
serious in Harbin. According to the National Air Quality Standard of China
(0.1mg/m3), 190 of the 246 residential houses violated the acceptable formaldehyde
concentration and needed to remove formaldehyde from indoor air, while only 22.8%
of the 246 residential houses met the acceptable formaldehyde concentration.
According to the responses from the residents, approximately 77% of them have
complained the irritation of eyes and fauces to some degree.
The measurement of indoor formaldehyde showed that poor air quality of residential
houses in Harbin resulted mainly from the furniture made of laminate board. In case
of good furniture quality, the formaldehyde concentrations in most of the decoration
house were less than 0.2 mg/m3 even if the floor was made of artificial board. The
indoor formaldehyde concentration of residential houses that had new furniture was
obviously higher than that had only old furniture. This study revealed that a close
correlation between indoor formaldehyde pollution, and quality of decorating
materials and furniture materials, and the status of ventilation was observed.
Owing to very few control efforts on indoor air quality, the formaldehyde
concentration has been maintained at high level in the residential houses throughout
4
Table 1. Statistical analysis of formaldehyde concentrations measured in the 246
residential houses in Harbin.
Range of
concentration
(mg/m3)
Overproof times
Sample number
(n)
Percentage
(%)
0.017~0.100
0.100~0.200
0.200~0.300
0.300~0.400
0.400~0.500
0.500~0.600
0
0~1
1~2
2~3
3~4
4~5
56
86
47
26
18
7
0
34. 96
19. 11
10. 57
7. 32
2. 85
0.600~0.700
0.700~0.800
0.800~1.00
5~6
6~7
7~9
5
0
0
2. 03
0
0
1.000~1.400
9~13
1
0.41
246
77.2
Total
Harbin. Thus, the development of effective purification means for formaldehyde in
indoor environments is highly required.
Correlation of Indoor Formaldehyde Concentration and Room
Temperature
The urea-formaldehyde resin has been widely used as an adhesive in the laminate
board and furniture. The resin could be decomposed and released formaldehyde
from the artificial board used in fitment room and furniture under the effect of room
temperature, humidity, light intensity, and etc. Previous studies reported that the
moisture and acidity substances significantly influence the destruction of the artificial
board in indoor enviroments.21-22
The formaldehyde emission rate of artificial board was significantly affected by room
temperature. The release of formaldehyde will be quick when room temperature is
high. On the contrary, the formaldehyde will be released slowly as room
temperature is low and will further release as room temperature rises. In general, the
amount of formaldehyde release became twice higher as the room temperature rose
5~6 ℃.21 However, the indoor formaldehyde concentration would fall quickly once
if there is frequent natural ventilation. The amount of formaldehyde release became
less as the room temperature was below 18 ℃. The formaldehyde tends to stay in
artificial board at low temperature. Thus, the duration of formaldehyde could be
extended and could exist in indoor air for a longer time.23
In Harbin, the winter lasts about half a year long (from November to March) and the
5
summer is relatively short (from June to August), which is the typical climate of the
chilly area in Northeast China.
The correlation of indoor formaldehyde
concentration and the room temperature monitored in the 246 residential houses was
further analyzed statistically in this study (see Table 2). The results showed that the
indoor formaldehyde concentration during the space heating period (from the end of
October to the end of April) was relatively low with the range of 0.134-0.198 mg/m3.
The monthly average formaldehyde concentration in May and September was 0.262
and 0.260 mg/m3, respectively. The monthly average value of formaldehyde
concentration in June, July and August were 0.380, 0.327 and 0.300 mg/m3,
respectively, which were the highest in the year. In general, the monthly average
formaldehyde concentration in summer (June~August) was about twice higher than
those in winter (November~December, January~March). There might be some
correlation between indoor formaldehyde concentration and room temperature, though
the monthly average indoor formaldehyde concentration varied throughout the year.
The comparison of the monthly average indoor formaldehyde concentration and room
temperature was undertaken to know the variation of the indoor formaldehyde
concentration with room temperature. The room temperature of the 246 residential
houses ranged from 8.0 to 29.0 ℃ and the monthly average indoor temperature
ranged from 17.0 to 26.5 ℃. The yearly average room temperature in Harbin was
21.5 ℃. A relatively strong correlation was observed as shown in Figure 2. It
shows that the trend of monthly average indoor formaldehyde concentration and room
temperature are quite similar. A linear regression model of monthly average indoor
formaldehyde concentration as a function of room temperature is shown in Figure 3
and can be expressed in equation (1).
C  0.0246T  0.304
(R2=0.8652)
(1)
where C is the monthly average indoor formaldehyde concentration, mg/m3;
monthly average room temperature, ℃
T is the
Table 2. Statistical analysis of indoor formaldehyde concentration in Harbin.
Sampling time
Spring (Apr.~May)
Summer (June~Aug.)
Fall (Sept.~Oct.)
Winter (Jan.~March,
Nov.~Dec.)
Non-heating period
Heating period
All the year
35
62
42
107
Concentration
range
(mg/m3)
0.054~0.631
0.078~1.302
0.031~0.679
0.017~0.448
121
125
246
0.062~1.302
0.017~0.448
0.017~1.302
Sample
number
0.222
0.336
0.207
0.154
Standard
Deviation
(mg/m3)
0.026
0.025
0.022
0.009
0.301
0.156
0.219
0.018
0.008
0.010
Average
(mg/m3)
Median
(mg/m3)
0.183
0.286
0.164
0.132
0.269
0.134
0.176
6
Figure 2. Monthly variation of indoor formaldehyde concentrations and room
temperature.
0.4
o
Room Temperature ( C)
3
Formaldehyde Concentration (mg/m )
30
0.3
20
0.2
10
0.1
Room Temperature
Concentration
0
0.0
Jan. Feb. Mar.Apr.MayJuneJulyAug.Sep. Oct. Nov.Dec.
Month
Figure 3. Correlation of monthly average formaldehyde concentration with room
temperature
3
Formaldehyde Concentration (mg/m )
0.4
0.3
0.2
0.1
2
R =0.8652
0.0
15
18
21
24
27
30
o
Room Temperature ( C)
7
.Environmental
Factors
that
Affect
Indoor
Formaldehyde
Concentration
The concentration of indoor formaldehyde might be affected by some environmental
factors. Indoor air quality varied with weather condition, outdoor air pollutant
concentration, and etc. The air exchange rate influences the emission rate of
formaldehyde from the sources and the duration for reducing air pollutant
concentration due to dilution effect.24-25 Moreover, the indoor air pollutant
concentration would increase with the decrease of the room volume. The
distribution of air pollutants in indoor environments is not uniform, which is
influenced by the location of emission sources and the circulation condition of indoor
air. The emission of formaldehyde increases with the increase of room temperature
and relative humidity. Therefore, room temperature and humidity are two major
factors that affect the indoor formaldehyde concentration.26 Air pressure is another
factor that indirectly affects the emission amount and concentration of indoor
formaldehyde resulting from the influence of moisture content. Approximately 50%
of total formaldehyde, which existing in the furniture and the artificial board used for
decoration, would be released within five years.27
Prediction of Indoor Formaldehyde Concentration
The measurement of indoor formaldehyde concentration and the investigation of its
influence factors were further conducted in fifty residential houses. Six major
factors including room temperature, relative humidity, air exchange rate, the surface
area of the board, the quality of the board and furniture, and the space of the room was
taken into consideration for their potential roles on the influences of the indoor
formaldehyde concentration. A mathematical model was developed based on the
dimension analysis of these factors and the detected indoor formaldehyde
concentration (equation (2)), which can then be used to predict the indoor
formaldehyde concentration.
C
fQ(rT  a)(bH  e)
N
(i  j )
G
(2)
where C is the indoor formaldehyde concentration, mg/m3; T is the room
temperature, ℃; H is the indoor relative humidity, g (H2O)/kg (dry air); Q is the
board quality level, ranging from 1 to 5; N is the air exchange times per hour, 0.1~1.0
times/h; G is the surface area of the board per volume (the surface area of the board
divided by the space volume of the room), m-1; r, a, b, e, f, i, j are the coefficients.
The non-linear regression of measured data was undertaken for the mathematical
model by using a statistical software. The results showed that the undetermined
coefficients of r, a, b, e, f, I, and j were 0.108, 0.907, 0.001, 0.193, 0.582, 1.401 and
1.093, respectively. Thus, the indoor formaldehyde concentration can be predicted
8
by equation (3).
C
0.582Q(0.108T  0.907)(0.001D  0.193)
N
1.401  1.093
G
(3)
In order to know the confidence level, 36 groups of detected data were substituted into
equation (3) and the predicted formaldehyde concentrations were obtained. The
comparison of the detected and predicted formaldehyde concentration is shown in
Figure 4. Comparison of the predicted and detected formaldehyde concentration
showed that the determination coefficient R2of regression is 0.8670 with a standard
deviation of 0.053 mg/m3. The detected formaldehyde concentration ranged from
0.036 to 0.610 mg/m3. The average and the standard deviation of the detected
formaldehyde concentration were 0.210 and 0.024 mg/m3, respectively. The
predicted formaldehyde concentration ranged from 0.059 to 0.612 mg/m3. The
average and the standard deviation were 0.198 and 0.023 mg/m3, respectively. It
concluded that the indoor formaldehyde concentration predicted by equation (3)
derived in this study was relatively accurate while compared to the detected data.
The indoor formaldehyde concentration can be predicted by equation (3) once if the
factors such as room temperature, relative humidity and air exchange frequency were
known. It implies that formaldehyde pollution in indoor environments can be
controlled during the design process. As indoor formaldehyde concentration is
predicted to be high, the sources of formaldehyde should be removed or replaced,
which were expected to emit much less or even no formaldehyde. In addition,
reducing the surface area of the artificial board and increasing ventilation frequency
might be also effective to reduce indoor formaldehyde concentration.
Duration of Indoor Formaldehyde Pollution
Health effects resulting from the exposure of indoor formaldehyde have been
associated primarily with irritant responses to the eyes, nasal and upper respiratory
tracts.28 Though the formaldehyde concentration in residential houses is very low,
some health effects would appear for long time exposure. Therefore, it is crucial to
know the duration of the formaldehyde in indoor environments. Experimental
results showed that the formaldehyde released from old artificial board was no less
than that from new artificial board.21 Therefore, in indoor environments, the release
of formaldehyde is persistent.
According to the above investigation, fifty residential houses in the Nangang district
of Harbin were selected for the measurement of indoor formaldehyde concentration.
All of these residential houses have been decorated to some degree. The variation of
indoor formaldehyde concentration with decoration time was investigated. The
decoration time was divided into five levels in order to investigate the variation of
indoor formaldehyde concentration with decoration time. The statistical analysis of
9
Figure 4. Verification of model predictions with the detected indoor formaldehyde
concentration.
3
Detected Data (mg/m )
0.8
0.6
0.4
0.2
2
R =0.8670
0.0
0.0
0.2
0.4
0.6
0.8
3
Predicted Data (mg/m )
these five levels was undertaken separately and summarized in Table 3. Results
from statistical analysis showed that there is no significant difference between the
indoor formaldehyde concentrations in the residential houses that have finished
decoration for 1, 3 and 8 months. Furthermore, no significant difference between the
formaldehyde concentration of residential houses that have finished decoration for 12
and 24 months was also observed. However, there is significant difference between
the indoor formaldehyde concentration in the residential houses that have finished
decoration for 8 and 12 months. The average concentration of indoor formaldehyde
in the houses that have finished decoration for one year was approximately 40.2% of
that in the houses that have finished decoration for one month. The average
formaldehyde concentration in the houses that have finished decoration for two years
was approximately 33.5% of that in houses that have finished decoration for one
month. The average indoor formaldehyde concentration in the houses that have
finished decoration for two years was approximately 1.6 times higher than the
National Air Quality Standard of China (0.10 mg/m3). It concluded that the duration
of indoor formaldehyde pollution was quite long in chilly area in Northeast China.
Exposure to formaldehyde could cause adverse effects on human health. Therefore,
the regulation that restricts the emission source of formaldehyde should be established.
Besides, residents should choose high quality decorating materials and furniture to
prevent the emission of formaldehyde. Moreover, the decorated residential houses
should be ventilated for an enough time before moving in the houses since the
formaldehyde can be removed by natural or forced ventilation.
10
Table 3. Formaldehyde concentration in fitment room with different decoration time.
Standard
Finished
Sample
Concentration
Average
Deviation
Months
Number
(mg/m3)
(mg/m3)
(mg/m3)
1
10
0.187~0.798
0.478
0.064
3
10
0.181~1.302
0.449
0.103
8
10
0.092~0.694
0.355
0.061
12
10
0.056~0.413
0.192
0.036
24
10
0.020~0.317
0.160
0.030
CONCLUSIONS
Results from indoor formaldehyde measurement in the residential houses in Harbin
showed that the formaldehyde was commonly observed in the houses with the range
of 0.017~1.302 mg/m3. The average indoor formaldehyde concentration in the year
was 0.219 mg/m3 and only 22.8% of the residential houses met the acceptable
formaldehyde concentration of 0.1 mg/m3 for National Air Quality Standard of China.
The highest formaldehyde concentration in indoor environments was observed in June
while the lowest was in November.
The monthly average formaldehyde
concentration ranged from 0.134 to 0.386 mg/m3, with the maximum in June and the
minimum in December. The indoor formaldehyde concentration in summer was
approximately twice higher than that in winter. It concluded that the indoor
formaldehyde pollution was very much serious in Harbin. The duration of indoor
formaldehyde pollution was quite long in Harbin. The indoor formaldehyde
concentration in the residential houses that finished decoration for 2 years was
approximately 1.6 times higher than National Air Quality Standard of China
(0.10mg/m3). It concluded that the formaldehyde could exist in indoor environments
for a long time and its concentration tended to decrease very slowly.
A strong correlation between the monthly average indoor formaldehyde concentration
and monthly average room temperature was obtained. The indoor formaldehyde
concentration increased with room temperature. A non-linear model base on the
dimension analysis of the detected data was successfully developed by considering the
factors of room temperature, relative humidity, air exchange rate, the surface area of
the board, the quality of the board and furniture and the space of room..
Formaldehyde concentration in indoor environments predicted by the model was
relatively accurate.
ACKNOWLEDGEMENTS
The authors would like to thank Ms. H. Ouyang and Ms. W.P. Li for their kind
assistances to accomplish this study. This investigation was performed under the
auspices of Indoor Health Technical Company Limited. The authors are grateful for
its constant support.
11
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Key Words
Indoor air pollution
Formaldehyde
Sampling and analysis
Correlation analysis
Model prediction
13