Yonago Acta medica 2014;57:133–136

Original Article

Assessment of Effects of Air Pollution on Daily Outpatient Visits using the Air
Quality Index
Haosheng Mu,* Shinji Otani,† Mikizo Okamoto,‡ Yae Yokoyama,* Yasuko Tokushima,§ Kazunari Onishi,*Takenobu Hosoda* and Youichi Kurozawa**Division of Health Administration and Promotion, Department of Social Medicine, School of Medicine, Tottori University Faculty of
Medicine, Yonago 683-8504, Japan, †Division of Surgical Oncology, Department of Surgery, School of Medicine, Tottori University
Faculty of Medicine, Yonago 683-8504, Japan, ‡Cancer Center, Tottori University Hospital, Yonago 683-8504, Japan and §Departmentof Nursing Care Environment and Mental Health, School of Health Science, Tottori University Faculty of Medicine, Yonago 683-8503,
Japan

ABSTRACT

air pollution, half of which occurred in the developingworld.1 Ambient air pollution is one of the major environmental problems in China, and from January 2013,a large area around Beijing has had the worst air quality, with the Beijing Environmental Protection Bureau
recording peak hourly PM2.5 (particulate matter withaerodynamic diameters less than 2.5 μm) above 400 μg/
m3 on 12 January, 2013.2 Previous studies reported that
an elevated level of ambient air pollution increased therisks of mortality and morbidity.3, 4
The air quality index (AQI) is widely used to characterize the quality of ambient air. AQI values are generally divided into ranges assigned with certain publichealth messages, mainly in order to meet air quality
management objectives.5 Chinese cities started to officially report the Air Pollution Index (API) on a daily
basis from 2000. The existing API is a variant of AQI,
which was adopted from 2012. The breakpoints for AQI
values are 50, 100, 150, 200 and 300, with an individual
score being assigned to the level of each pollutant.
Higher numerical values indicate increasingly serious
pollution, with values more than 100 representing an
unhealthy environment for sensitive groups. This index
involves PM10, PM2.5, sulfur dioxide (SO2), nitrogendioxide (NO2), and ozone (O3). Acute exposure to thesepollutants has been associated with increased adverse
health endpoints such as increased cardiorespiratory
mortality and morbidity rates in several large multicity
studies in Europe, North America, and Asian cities.6–9
However, few studies have evaluated morbidity risks
using the AQI. The objective of this study was to assess
the association between AQI and daily outpatient visits.

Background

The air quality index (AQI) is widelyused to characterize the quality of ambient air. Chinese
cities officially report the AQI on a daily basis. To assess
the possible effects of air pollution on daily outpatient
visits, we examined the association between AQI andthe daily outpatient count.
Methods Daily data on outpatient visits to each clinical department were collected from the Z county hospital of Datong City, China. The collection period was
between 5 April and 30 June, 2012. Daily AQI data
and meteorological information were simultaneously
recorded. We compared outpatient counts between theindex days and comparison days, and calculated Pearson’s product moment correlation coefficient between
outpatient counts and AQI levels.
Results
The average AQI level for index days was
significantly higher than that for comparison days. No
significant difference was observed in temperature or
relative humidity between index days and comparisondays. The outpatient counts for pediatrics were significantly higher on index days than on comparison days,
and no significant difference was noted in other clinicaldepartments. The outpatient counts for pediatrics positively correlated with the AQI level, and no correlation
was noted in other clinical departments.
Conclusion The present study assessed the association between daily outpatient visits and air pollution using AQI. The results obtained suggest that air pollution
could increase the outpatient count for pediatrics.
Key words

air pollution; air quality index; daily out-

patient visit
SUBJECTS AND METHODS
Data sources

The World Health Organization estimated that morethan 2 million deaths annually could be attributed to

We chose Z county of Datong city as our study site. Z
county, which is located in the northern part of Datongcity, China, is well-known for its coal mining industry.
Therefore, some industrial pollutants in this district arecaused by coal particles and carbon dioxide (CO2). It is
an ideal candidate site to study the effects of air pollu-

Corresponding author: Haosheng Mu, MD
muhs@med.tottori-u.ac.jp
Received 2014 September 26
Accepted 2014 October 9Abbreviation: AQI, air quality index

133

H. Mu et al.

tion on health. The county covers an area of 137.58 km2
and has a population of 55,031. There are two general
hospitals and 23 clinics in this county. Because thecounty is near Datong, patients also went to the hospitals
in Datong City in the case of serious illness.
We chose the biggest county hospital as our researchorganization. The counts of total daily outpatient visitswere provided by the county hospital. The study subjects
were all people who came to each clinical department
including respiratory medicine, pediatrics, dermatology,
ophthalmology, and otorhinolaryngology. Surgery, cardiology and gastroenterology were excluded. The survey
period was between 5 April, 2012 and 30 June, 2012.
The air pollution occurs frequently in the winter season.
This survey was to be conducted in spring season, because air pollution occurs sometimes during this time,
and the relations with the outpatient visits are easy to befound. Daily AQI data and daily information on temperature (˚C) and relative humidity (%) were released at the
Datong Environmental Monitoring Center10 and China
Meteorological Administration,11 and were simultaneously collected from the website.

88.3 ± 49.2**
13.5 ± 3.7
36.2 ± 12.8

48.9 ± 18.5
14.7 ± 3.8
41.8 ± 19.6

Outpatient count

10
5

logy
tory
cs
logy
noiatri rmato thamo Otorhi gy
p
e
Ped
lo
O
D
ngo
lary

Fig. 1. Comparison of outpatient count in each clinical department
between index days and comparison days. *P < 0.05.

RESULTS
Table 1 shows the average values of AQI levels, temperature and relative humidity for index days and comparison days. The average AQI level for index days was
significantly higher (P < 0.01) than that for comparisondays. No significant difference was observed in temperature or relative humidity between index days and comparison days.
Figure 1 shows the distribution of outpatient counts
in each clinical department between index days andcomparison days. The outpatient counts for pediatrics onindex days (16.13 ± 5.12) was significantly higher thanthat on comparison days (12.47 ± 3.74; P < 0.05), and no
significant difference was noted in other clinical departments.
The correlation coefficients between AQI levels andrespiratory medicine, pediatrics, dermatology, ophthalmology and otorhinolaryngology outpatient counts were0.030, 0.387, 0.012, –0.050 and 0.120, respectively. The
outpatient count for pediatrics correlated with the AQI30

Outpatient countfor pediatrics

AQI
Temperature (˚C)
Humidity (%)

15

pira

Table 1. Average values of the air quality index (AQI),
temperature, and relative humidity on index and comparison days
Comparison days(n = 57)

20

Res

There were 14 clinic holidays between 5 April and 30
June, 2012; therefore, there were 73 days for the analysis. In total, 6 air pollution days (AQI values more than100) were noted. The effects of air pollution, if any, canbe delayed over a period of several days. To test this hypothesis, we examined the effects on the same day, and
1 and 2 days after the air pollution days, and these days
were defined as index days.
Outpatient counts on the index days were comparedwith outpatient counts on the comparison days (days except the index days) in the primary analysis. T tests wereused to make comparisons between index days and comparison days because these parameters were normally
distributed. Pearson’s product moment correlation coefficient was used to determine the correlation between
outpatient counts and AQI levels. All data analyses were
performed using SPSS version 19.0 (IBM SPSS, Chicago, IL), and a significance level of 5% was used.

Index days(n = 16)

Comparison days
Index days

0

Statistical analysis

Variable

*

25

25
20
15
10
5
0

0

50

100

150

200

250

AQI

Fig. 2. Correlation between the outpatient count for pediatrics andthe air quality index levels (R2 = 0.150, P < 0.01). AQI, air quality
index.

Values are mean ± SD.
**Significant difference in comparison days (P < 0.01).

134

250

Outpatient count for pediatrics

25
20
15

100

10

level (R2 = 0.150; P < 0.01; Fig. 2). Time-series of AQI
and the outpatient count for pediatrics from 5 April,2012 to 30 June, 2012 is presented in Fig. 3.

28-Jun21-Jun14-Jun7-Jun

31-May24-May17-May10-May

0

3-May

0

26-Apr5

19-Apr50

12-AprFig. 3. Time-series of AQI and the outpatient count for pediatrics from 5 April, 2012
to 30 June, 2012 (blanks in the line of outpatient count for pediatrics, off days of thehospital). AQI, air quality index.

30

150

5-Apr

AQI

200

AQI

Outpatient countEffects of air pollution on daily outpatient

ing in households, are confounding factors. The present
study assumed that all individuals were equally andevenly exposed to particulate matter derived from outdoor air pollution and occupational and indoor personal
exposures were considered to be either marginal orconstant over time. Secondly, each pollutant (e.g., PM2.5,
NO2 and SO2) and meteorological variables (e.g., atmospheric pressure) also may have effect on the outpatient
visits. These factors were not considered in this study.
Finally, because this study only included one hospital,
the sample size was small. These limitations may haveresulted in some bias in the magnitude of the relationship between air pollution and human health outcomes;
however, we expect that the general trends found in thepresent study would be unchanged.
In the present study, we assessed the association between daily outpatient visits and air pollution using AQI.
The results obtained suggest that air pollution could increase the outpatient count for pediatrics.

DISCUSSION
Numerous recent studies have assessed the adverse effects of air pollution on elderly people and patients withchronic disease, including mortality, hospital admissions, and emergency hospital visits.12–15 This study assessed the possible effect of air pollution on the healthof the general population according to daily outpatient
counts.
The results obtained revealed a correlation between
AQI and the outpatient count for pediatrics, which indicated that air pollution increased the outpatient count forpediatrics. A number of epidemiological studies demonstrated that exposure to air pollution causes an increase
in respiratory diseases.16–19 Other studies showed that
respiratory defenses became compromised, respiratory
resistance decreased, and respiratory inflammation occurred after a child inhaled particulate matter comprising SO2, Nox and O3.20– 22
Children have the following characteristics: A, they
are more active than adults; B, they breath more air per
body weight than adults; C, their respiratory organs arestill developing; and D, the asthma ratio is higher thanthat in adults. Therefore, children are at a higher risk ofdeveloping disorders associated with air pollution thanadults. Li and co-authors concluded that increases in
PM10, NO2 and O3 pollution levels could lead to a corresponding increase in the hospitalization of children.23
Our result supports this finding. Children will need totake some preventive action such as wearing a mask andthe closure of schools due to air pollution based on the
AQI level in everyday life.
There are several limitations to the present study.
Firstly, both occupational exposure and indoor air pollution, such as smoking, fuel used for cooking and heat-Acknowledgments: The authors wish to cordially thank Doctor Li
Hai and other staff at the Zuoyun County Hospital for providing
assistance on the collected outpatient data in Zuoyun. This work
was supported by the Assessment and control of dust emission indegraded Drylands of east Asia, Tottori University.
The authors declare no conflict of interest.
References
1 Chen R, Wang X, Meng X, Hua J, Zhou Z. Communicating
air pollution-related health risks to the public: An applicationof the Air Quality Health Index in Shanghai, China. Environ
Int. 2013;51:168-73. doi: 10.1016/j.envint.2012.11.008.
2 Air quality forecast [Internet]. Beijing: Beijing Municipal
Environmental Monitoring Center; c2013 [cited 2013 Jan 12].
Available from: http://www.bjmemc.com.cn/.
3 Santos UP, Terra-Filho M, Lin CA, Pereira LA, Vieira TC,
Saldiva PH, et al. Cardiac arrhythmia emergency room visitsand environmental air pollution in Sao Paulo, Brazil. J Epidemiol Community Health. 2008;62:267-72. doi: 10.1136/
jech.2006.058123.

135

H. Mu et al.
4 Szyszkowicz M. Ambient air pollution and daily emergency
department visits for ischemic stroke in Edmonton, Canada.
Int J Occup Med Environ Health. 2008;21:295-300. doi:
10.2478/v10001-008-0029-5.
5 Air quality forecast [Internet]. Beijing: China National Environmental Monitoring Center; c2012 [cited 2012 Feb 6].
Available from: http://www.cnemc.cn/.
6 Bell ML, McDermott A, Zeger SL, Samet JM, Dominici F.
Ozone and short-term mortality in 95 US urban communities,
1987–2000. JAMA. 2004;292:2372-8.
7 Chen R, Kan H, Chen B, Huang W, Bai Z, Song G, et al. Association of particulate air pollution with daily mortality: thechina air pollution and health effects study. Am J Epidemiol.
2012;175:1173-81. doi: 10.1093/aje/kwr425.
8 Dominici F, Peng RD, Bell ML, Pham L, McDermott A,
Zeger SL, et al. Fine particulate air pollution and hospital
admission for cardiovascular and respiratory diseases. JAMA.
2006;295:1127-34.
9 Samoli E, Peng R, Ramsay T, Pipikou M, Touloumi G,
Dominici F, et al. Acute effects of ambient particulate matteron mortality in Europe and North America: results from the
APHENA study. Environ Health Perspect. 2008;116:1480-6.
doi: 10.1289/ehp.11345.
10 Air quality forecast [Internet]. Datong: Datong Environmental
Monitoring Center; c2012 [cited 2012 Jun 30]. Available from:http://www.dtems.org.cn/main.asp.
11 Weather forecast [Internet]. Beijing: China Meteorological
Administration; c2012 [cited 2012 Jun 30]. Available from:http://www.weather.com.cn/.
12 Guo Y, Jia Y, Pan X, Liu L, Wichmann HE. The association
between fine particulate air pollution and hospital emergency room visits for cardiovascular diseases in Beijing,
China. Sci Total Environ. 2009;407:4826-30. doi: 10.1016/
j.scitotenv.2009.05.022.

13 Simkhovich BZ, Kleinman MT, Kloner RA. Particulate air
pollution and coronary heart disease. Curr Opin Cardiol.
2009;24:604-609. doi: 10.1097/HCO.0b013e32833161e5.
14 Oudin A, Stroh E, Stromberg U, Jakobsson K, Bjork J. Longterm exposure to air pollution and hospital admissions forischemic stroke. A registerbased case-control study using
modelled NO(x) as exposure proxy. BMC Public Health.2009;
9:301. doi: 10.1186/1471-2458-9-301.
15 Halonen JI, Lanki T, Yli-Tuomi T, Tiittanen P, Kulmala
M, Pekkanen J. Particulate air pollution and acute cardiorespiratory hospital admissions and mortality among
the elderly. Epidemiology. 2009;20:143-53. doi: 10.1097/
EDE.0b013e31818c7237.
16 Schwela D. Air pollution and health in urban areas. Rev Environ Health. 2000;15:13-42.
17 Oberdorster G. Pulmonary effects of inhaled ultrafine particles. Int Arch Occup Environ Health. 2001;74:1-8.
18 Furtaw EJ Jr. An overview of human exposure modelingactivities at the USEPA’s National Exposure Research Laboratory. Toxicol Ind Health. 2001;17:302-14.
19 Chen Y, Yang Q, Krewski D, Shi Y, Burnett RT, McGrail K.
Influence of relatively low level of particulate air pollution
on hospitalization for COPD in elderly people. Inhal Toxicol.
2004;6:21-5.
20 Xiao C, Han X, Xi S, Wang R, Ma G, Wei D. Analysis on
effects of air pollution on microecology of children’s upper
respiratory tract. Chin Public Health. 2002;18: 1457-8.
21 Zhu Y, Yang X, Li Y. Relationship between air pollution andchildren respiratory diseases in a certain area in Shenyang. J
Environ Health. 2008;125:575-8.
22 Chen B, Hong C, Zhu H. Quantitative assessment of impactof ambient air nitrogen oxides on human health in Shanghai.
Shanghai Environ Scien. 2002;21:129-31.
23 Li N, Zhang B, Peng X. Relationship between air pollution
and hospitalization of children respiratory disease in Shenzhen City. Chin J Public Health. 2009;25:1504-15.

136