Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

ReportChanges in Particulate Matter (PM2.5 and PM10) Concentrations
and Ambient Dose Equivalent Rates at Different Altitudes
in Chiang Mai, Thailand
Chutima Kranrod1, Tarika Thumvijit 2, Ryohei Yamada1, Worawat Poltabtim1, 3,
Mizuki Kiso1, 3, Sompong Sriburee2, Siriprapa Somboon2, Kewalin Ruktinnakorn2
and Shinji Tokonami1*
1
Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai 50200, Thailand
3
Department of Radiation Science, Graduate School of Health Sciences, Hirosaki University, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
2

Received 16 October, 2023; revised 24 November, 2023; accepted 5 December, 2023

Air pollution is one of the biggest problems in many cities worldwide. Chiang Mai is a city that
also faces this problem, especially during the dry season. Due to its topography, Chiang Mai has
various elevation areas, resulting in the dispersion of pollution at different altitude locations thatshould be measured in order to evaluate health hazards at different locations. In this study, theconcentrations of PM2.5 and PM10 were measured at different altitudes in Chiang Mai, Thailand.
At the same time, the ambient dose equivalent rate was monitored. The measurement results
showed that the average concentration of PM2.5 and PM10 around urban areas was 23±13 µg m-3
and 47±18 µg m-3, respectively, and was 14±9 µg m-3 and 29±14 µg m-3, respectively, aroundoutside urban areas. Moreover, a minor effect of altitude was observed from the measurement
locations outside urban areas. The PM2.5 and PM10 concentrations tend to increase withincreasing altitude. However, there was no significant difference in ambient dose equivalent rates
at different altitudes. The average ambient dose equivalent rate in this study was observed atabout 95±12 nSv h-1.
Key words: pollution, PM2.5, PM10, ambient dose equivalent rate, altitude

1. Introduction
With the continuous development of the city and rapid
urbanization and industrialization, Chiang Mai province,
Thailand, has become one of the few cities with themost severe air pollution in the world. Chiang Mai is the*Shinji Tokonami: Institute of Radiation Emergency Medicine, Hirosaki University,
66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
E-mail: tokonami@hirosaki-u.ac.jp
https://doi.org/10.51083/radiatenvironmed.13.1_28
Copyright © 2024 by Hirosaki University. All rights reserved.

second-largest city in Thailand with a population of 1.7
million, and it has been a popular tourist destination formany decades due to its topography, climate, and cultural
history. Since the last decade, Chiang Mai has been facing
severe air pollution, especially during the dry seasonfrom February to May every year. Among air pollution,
particulate matter (also called PM) is a major concern topublic health. PM is the term for particles found in theair, including solid dust, smoke, and liquid droplets. The
toxicity of PM is mainly due to particles with a diameterof less than 10 µm (PM10). Among these, PM2.5 particles

Chutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

with a diameter of less than 2.5 µm have raised significant
concerns about their impact on public health1).
There were many days during the dry season in
Chiang Mai when PM10 had reached 200 µg m-3 or over2).
It should be noted that the Environmental Protection
Agency (EPA) recommended the PM10 standard levelshould not exceed 150 µg m-3 over 24 hours3). Several
researchers confirmed that the major source of ambient
PM2.5 in Chiang Mai City during the dry season was
mostly produced by the burning of biomass4-6). This issue
has had a significant impact on Chiang Mai, not only
on the economic and tourist industries, but as well as
tremendously on public health, both short- and long-term.
Ambient air pollution is a major risk factor for theenvironmental threat to human health. Air pollution refers
to the air that is contaminated with harmful pollutants
or substances that are produced from natural sources
such as radon gas and its progeny or from anthropogenic(man-made) sources such as the combustion of fuels in
vehicles or industry production processes7). According
to data from the World Health Organization (WHO),
more than 90% of the worldʼs population breathes air
containing pollutants that adversely affect human health,and more than 6 million premature deaths annually areassociated with air pollution8). This mortality is mostly
due to exposure to PM, especially PM2.5 and PM10 which
penetrate deep into lung passageways, and increase therisk of the burden of disease from stroke, cardiovasculardisease, lung cancer, and both chronic and acuterespiratory diseases9-11).
Several research reported that the size and compositionof PM vary widely in the atmosphere depending on
the different meteorological conditions and could
cause various health hazards in different locations12, 13).
Furthermore, various meteorological and geographicalparameters such as air temperature, altitude, and radiation
are also involved in the dispersion and concentration of
PM in the atmosphere14). There are several studies thathave reported the altitude distribution that determines
PM concentrations. Zona and team15) reported that thehighest average concentrations of PM2.5 were observedat the highest elevation areas, while the lowest averages
were obtained at the low elevation areas near the seaside.
On the contrary, Muhammad and his team16) showed that
the PM concentration decreased with increasing altitude.
The geographical features of Chiang Mai province
have various elevation areas due to its location in anatural basin surrounded by high mountain ranges,
therefore, the dispersion of PM concentrations at different
altitudes should be measured in order to evaluate
health hazards at different locations. In this study, theconcentrations of PM2.5 and PM10 were measured at
different altitudinal levels in Chiang Mai, Thailand toinvestigate the correlations between the altitude levels

29

and the concentrations of PM2.5 and PM10. Furthermore,
the measurement of the ambient dose equivalent rate
at different altitudes was performed together with themeasurement of PM in order to study the relationshipbetween the ambient dose equivalent rate and PM
concentration at different altitudes. The ambient dose
equivalent rate is related to natural background radiationsuch as radon, cosmic rays, and terrestrial gamma
rays, and exposure to natural background radiation isconsidered as a factor in increasing the risk hazard to
public health17).
2. Materials and methods
2.1. Study areas
The measurements of PM concentration and ambient
dose equivalent rate were performed in typical public
outdoor areas of Chaing Mai province, Thailand. The
measurement locations can be categorized into twogroups: the urban areas group and the outside urban
areas group. The measurement locations in the urban
areas group are located in the urban areas of Chiang
Mai City, which covers around 40 km² of the Mueang
Chiang Mai district in the city center. Figure 1 shows
the measurement locations, which were recorded
as coordinates using the Google Maps application
on a smar tphone during the measurements at 10
measurement points around Chaing Mai province. The
map was plotted using free software, the Google Earth
Pro software (version 7.1). The coordinates and altitudesof the measurement locations are shown in Table 1. The
measurements were conducted on Februar y 2–8, 2023.
The weather was cool in the morning but hot during theday, with clear skies throughout the entire measurement
period. The temperature, humidity, and pressure during
the measurements were monitored on the website of
Weather Underground (available access from https://www.wunderground.com/histor y/weekly/th/mueangchiang-mai). The average temperature, humidity, and sea
level pressure were reported at around 25.6±8.4 °C, 57.8± 32.3 %, and 975.1±2.9 hPa, respectively.
2.2. Measurement method
The PM2.5 and PM10 concentrations were measured
using a portable air quality monitor (Aeroqual Series
500; Aeroqual Inc., New Zealand). Aeroqual Series 500 is
designed for portable, accurate, and real-time surveyingof common outdoor pollutants such as PM2.5, PM10, andCO2. During the measurement, the Aeroqual monitor
was handheld approximately 1 m above the ground. The
Aeroqual monitor was programmed to continuously
measure 5-minute average concentrations of PM2.5
and PM10, and the measurement was performed for 5
measurement cycles at a measurement location. Data

30

Chutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

Fig. 1. Map of measurement locations in Chiang Mai province, Thailand.

Table 1. Location and description of the study areas
No.

Name

Latitude(°N)

Longitude(°
E)

Altitude(m.a.s.l)*1

Location No.1

18.3523

98.29142560

Description
The top of Inthanon Mountain was surrounded by forest.

2

Location No.2

18.323998.31041290

A small village in the Doi Inthanon National Park.

3

Location No.3

18.331598.5055300

Urban area

4

Location No.4

18.400798.5533

310

Urban area

5

Location No.5

18.3860

98.5632300

Urban area

6

Location No.6

18.4216

98.5759

320

Urban area near the airport

7

Location No.7

18.4157

98.5813

310

Urban area near the airport

8

Location No.8

18.194298.2143850

A small village in the Mae Chaem district, near the Doi Inthanon National Park.

9

Location No.9

18.190798.2127820

A small village in the Mae Chaem district, near the Doi Inthanon National Park.

10

Location No.10

18.2633

98.2338

560

A small village near the Doi Inthanon National Park.

* Meter above the sea level (m.a.s.l)were stored on board the monitor and downloaded after
completed measurements via the Aeroqual software to alaptop.
The ambient dose equivalent rates were measured
using a survey meter (1 in×1 in cylindrical NaI(Tl)scintillation, TCS-171; Hitachi, Ltd.; Tokyo, Japan).
Notably, this portable NaI(Tl) scintillation survey meterhas been generally used in survey projects of the ambient
dose equivalent rate distribution17, 18). This survey meter
was calibrated using a 137Cs source. The calibration
factor was 0.98 for a dose rate range below 1 µSv h-1.
The ambient dose equivalent rate measurements wereconducted 1 m above the ground for five measurements
in five different directions at each measurement location,with the time constant of a measurement being 30 s.

3. Results and discussions
3.1. Altitudinal variation of PM2.5 and PM10
The average concentrations of PM2.5 and PM10 at
dif ferent altitudes ranging from 300 to 2560 m.a.s.l.
were measured to investigate the relationship between
the PM concentration and altitude. The altitude of themeasurement locations in the urban areas is about
300 m.a.s.l., and at these locations were obser ved theconcentrations of PM2.5 and PM10 in the range 10–44µg m-3 with an average of 23±13 µg m-3 and 30–75 µg m-3
with an average of 47±18 µg m -3, respectively. For
the measurement locations in the outside urban areas
group, the altitudes range from 560 to 2560 m.a.s.l. The
concentrations of PM2.5 and PM10 observed in this groupChutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

(A)

31

(B)

Fig. 2. Variations of (A) PM2.5 and (B) PM10 concentrations at different altitudes.

Fig. 3. Atmospheric profile across Chiang Mai province in the dry season.

ranged from 3–26 µg m-3 with an average of 14±9 µg m-3
and 12–52 µg m -3 with an average of 29±14 µg m -3,
respectively, as shown in Figure 2.
The observed PM concentrations showed that the
average PM concentrations in urban areas are higher
than those observed outside urban areas for both PM2.5
and PM10. A similar result was found by Khamkaew
et al.6), in which they found that the average PM2.5
concentration at Chiang Mai University (an urban area)
was higher than that at Doi Ang Khang (an outside urbanarea). They also revealed that biomass burning was amajor source of PM2.5 in Chiang Mai City during thedry season, which is probably caused by large areas ofopen burning in the upper part of Northern Thailand andneighboring countries. This is probably because Chiang

Mai City (the urban area) is situated in a natural basin
area at a low altitude ( <500 m.a.s.l.) surrounded by highmountains. During the dry season, the Asian WinterMonsoon circulates two main airflow channels, as shownin Figure 3, one at about 500 m.a.s.l., originating from theNorth-East and passing through from Laos, and anotherone at 3000 m.a.s.l., originating from the North-West andpassing through from Myanmar19). These seasonal winds
are responsible for bringing pollution from Laos into theeastern part of Chaing Mai (urban areas group) and from
Myanmar into the western part of Chiang Mai (outside
urban areas group)19). Due to the topography of Chiang
Mai City with its valleys and basins, the winds are limited,
and PM cannot be dispersed and keeps accumulating20).
This atmospheric dynamic explains why PM accumulates

32

Chutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

Fig. 4. The plot of ambient dose equivalent rates at different altitudes.
The solid line denotes an average value of the ambient dose equivalentrate. The dashed lines denote the expanded uncertainty of the meanvalue (k = 2).

in basins in Chiang Mai urban areas, and it also explainsvariations in some spatial heterogeneities of PMconcentrations.
Furthermore, the observed results showed that
altitude has a minor effect on the distribution of PMconcentrations in the measurement locations outside
urban areas with altitudes of 560 – 2560 m.a.s.l. As can beseen in Figure 2, the concentration of PM2.5 and PM10
tends to increase with increasing altitude. As mentioned
above, the wind at an altitude of 3000 m.a.s.l. has becomea significant carrier of pollution from Myanmar into thewestern part of Chiang Mai, which is the measurement
location of the outside urban areas group. Moreover,pollution from forest fires and burning of agriculturalresidues tends to travel to high altitudes due to the
expansion of industrial crops such as soybean and maize
monoculture, which has increased dramatically in thehighlands of this area. Choommanivong et al. 21) proposed
an atmospheric model that shows biomass burning inSoutheast Asia travels to an altitude of up to 3000 m.
Therefore, the PM concentration at higher altitudes
tends to be greater than at lower altitudes in this area. A
similar result was found by Zona et al.15), they observed
the highest average PM2.5 concentrations at the highest
elevation areas, while the lowest averages were observedat the low elevation areas near the seaside. Although
they mentioned that their research still does not provide
sufficient data on the behavior of PM at different
elevations, but they pointed out that this behavior might
be related to turbulence caused by the thermal-dynamic
properties of the air, which affect the transport ofaerosols.

3.2. Ambient dose equivalent rate
The ambient dose equivalent rate at different altitudes in
Chiang Mai City is shown in Figure 4. The ambient dose
equivalent rates in this study area were observed in therange of 80–110 nSv h-1 with an average value of 95±12
nSv h-1. The absorbed dose rates in air were estimated in
the range 64–90 nGy h-1, with an average of 77±10 nGy
h-1 using a dose conversion factor of about 1.23 Sv Gy -1
from the ICRP Publication 11622). According to the report
data from UNSCEAR (2000)23), the worldʼs absorbed
dose rates in the air are in the range of 24 to 160 nGy h-1,
with an average of 57 nGy h-1, which is a little lower than
the average value obtained in this study. The averageabsorbed dose rate obtained in this study was also slightly
higher than the average value obser ved in the eastern,western, and southern par ts of Thailand, which wasreported by Kranrod et al.24) with an average value of 41±
4 nGy h-1. This is because Chiang Mai is located in a highradon potential area25) and situated in a basin of graniterock associated with active faults26, 27). Therefore, thenatural background radiation from radon and its progeny,
and particularly terrestrial radiation from granite rocks,
may contribute to the radiation doses in the Chaing Mai
area more than in other parts of Thailand.
Figure 4 shows the plot of ambient dose equivalent
rates at dif ferent altitudes. The measurement results
were statistically compared using t-tests. A dif ferenceof p < 0.05 was considered statistically significant. The
results showed that no significant difference was foundin ambient dose equivalent rates at dif ferent altitudes;
therefore, no cor relation bet ween ambient dose
equivalent rate and altitude was observed in this study.
4. Conclusions
In this study, the concentrations of PM2.5 and PM10 were
measured together with the ambient dose equivalent rate
at different altitudes (ranging from 300 to 2560 m.a.s.l.) in
Chiang Mai, Thailand. The measurement locations weredivided into two groups: the urban areas group and theoutside urban areas group. The average concentration of
PM2.5 and PM10 in the urban areas group was (23±13)µg m-3 and (47±18) µg m-3, respectively, which is higher
than the average value of the outside urban areas group.
The average concentration of PM2.5 and PM10 in theoutside urban areas group was (14±9) µg m-3 and (29±14) µg m-3, respectively. Moreover, the obser ved results
showed that altitude has a minor effect on the distributionof PM concentrations in the measurement locations
outside urban areas with altitudes 560 – 2560 m.a.s.l., theconcentrations of PM2.5 and PM10 tend to increase withincreasing altitude. However, there was no significant
dif ference in ambient dose equivalent rates at dif ferent
altitudes. The ambient dose equivalent rates in this study

Chutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34

area were obser ved in the range of 0.080 – 0.110 µSv h-1
with an average value of 0.095±0.012 µSv h -1. The
variation of PM2.5 and PM10 concentrations and ambient
dose equivalent rates at dif ferent altitudes obtained inthis study provided useful information to Chaing Mai
residents and tourists. The information on PM2.5, PM10,
and radiation exposure levels is essential and interestingfor developing a pollution prevention and radiologicalprotection culture among citizens and engaging in a
dialogue on the policy to control pollution.

Dev. 2016;7(6):436–40.
7.

Koren H, Bisesi MS. Handbook of Environmental Health, Two
Volume Set. 4th ed. Boca Raton: CRC Press; 2019.

8.

World Health Organization. 9 out of 10 People Worldwide Breathe
Polluted Air, but More Countries Are Taking Action. [news on theInternet]. c2023 [updated 2018 May 2; cited 2023 Oct 3]; Available
from: https://www.emro.who.int/media/news/9-out-of-10-peopleworldwide-breathe-polluted-air.html.

9.

Int Panis L, Provost EB, Cox B, Louwies T, Laeremans M,
Standaert A, et al. Short-term air pollution exposure decreases
lung function: a repeated measures study in healthy adults.
Environ Heal. 2017;16(1):60.

10.

Münzel T, Gori T, Al-Kindi S, Deanﬁeld J, Lelieveld J, Daiber A,
et al. Effects of gaseous and solid constituents of air pollution on
endothelial function. Eur Heart J. 2018;39(38):3543–50.

11.

Mustafić H, Jabre P, Caussin C, Murad MH, Escolano S, Taf fletM, et al. Main air pollutants and myocardial infarction. JAMA.
2012;307(7):713.

12.

Lelieveld J, Evans JS, Fnais M, Giannadaki D, Pozzer A. The
contribution of outdoor air pollution sources to premature
mortality on a global scale. Nature. 2015;525(7569):367–71.

13.

Zhao B, Wu W, Wang S, Xing J, Chang X, Liou KN, et al. A
modeling study of the nonlinear response of ﬁne particles to air
pollutant emissions in the Beijing–Tianjin–Hebei region. Atmos
Chem Phys. 2017;17(19):12031–50.

14.

Zeb B, Alam K, Sorooshian A, Blaschke T, Ahmad I, Shahid I. On
the morphology and composition of particulate matter in an urban
environment. Aerosol Air Qual Res. 2018;18(6):1431.

15.

Zona Z, Ali Z, Zainab I, Sidra S, Raza ST, Ahmad M, et al. Changes
in particulate matter concentrations at different altitudinal levels
with environmental dynamics. J Anim Plant Sci. 2015;25(3):620–27.

16.

Muhammad M, Said RS, Tijjani BI, Idris M, Sani M. Investigating
the ef fect of altitude and meteorological parameters on theconcentration of particulate matter at an urban area of Kano State,
Nigeria. Bayero J Pure Appl Sci. 2022;13(1):400–8.

17.

Poltabtim W, Musikawan S, Thumwong A, Omori Y, Kranrod
C, Hosoda M, et al. Estimation of ambient dose equivalent rate
distribution map using walking survey technique in Hirosaki City,
Aomori, Japan. Int J Environ Res Public Health. 2023;20(3):2657.

18.

Yamaguchi K, Radiation Sur vey Team of Fukushima Univesity.
Investigations on radioactive substances released from the
Fukushima Daiichi nuclear power plant. Fukushima J Med Sci.
2011;57(2):75–80.

19.

Amnuaylojaroen T, Inkom J, Janta R, Surapipith V. Long range
transpor t of southeast Asian PM2.5 pollution to Nor thern
Thailand during high biomass burning episodes. Sustainability.
2020;12(23):10049.

Acknowledgements
This research was made possible with support from theFaculty of Associated Medical Sciences, Chiang Mai
University, Thailand, for the visiting professor program(Prof. Dr. Shinji Tokonami). In addition, this work waspartially supported by JSPS KAKENHI Grant Numbers
JP16K15368 and JP20H00556.
Author Contributions
Conceptualization, S.T. and C.K.; Methodology, R.Y.;
Formal analysis, M.K., and W.P.; Investigation, R.Y., C.K.,
T.T., S.S., S.S., K.R., P.B. and S.T.; Data acquisition andinterpretation, C.K. and W.P.; Supervision, C.K. and S.T.;
Validation, W.P., C.K. and S.T.; Writing-original draft, C.K.,
and W.P.; Writing-review and editing, C.K., W.P., and S.T.
All authors have read and agreed to the published versionof the manuscript.
Conflicts of Interest
The authors declare no conflict of interest.

33

References
1.

Pope CA, Dockery DW. Health effects of fine particulate
air pollution: lines that connect. J Air Waste Manag Assoc
2006;56(6):709–42.

2.

Pardthaisong L, Sin-Ampol P, Suwanprasit C, Charoenpanyanet
A. Haze pollution in Chiang Mai, Thailand: a road to resilience.
Procedia Eng 2018;212:85–92.

20.

3.

Environmental Protection Agency. NAAQS Table | US EPA[Internet]. [cited 2023 Oct 3]; Available from: https://www.epa.
gov/criteria-air-pollutants/naaqs-table.

Amnauylawjarurn T, Kreasuwun J, Towta S, Siriwitayakorn K.
Dispersion of particulate matter (PM10) from forest ﬁre in Chiang
Mai Province, Thailand. Chiang Mai J Sci. 2009;31(1):39–47.

21.

4.

Kawichai S, Prapamontol T, Cao F, Song W, Zhang Y. Source
identification of PM2.5 during a smoke haze period in Chiang
Mai, Thailand, using stable carbon and nitrogen isotopes. Atmos.
2022;13(7):1149.

Choommanivong S, Wiriya W, Chantara S. Transboundar y air
pollution in relation to open burning in Upper Southeast Asia.
Environ Asia. 2019;12:18–27.

22.

ICRP Conversion Coef ficients for Radiological Protection
Quantities for External Radiation Exposures. ICRP Publication
116. Ann ICRP 40. St. Louis: Elsevier; 2010.

5.

Kawichai S, Cao F, Song W, Kiatwattanacharoen S. Significant
Contribution of C3 - Type Forest Plantsʼ Burning to Airborne
PM2.5 Pollutions in Chiang Mai Province, Northern Thailand.
2020. [cited 2023 Oct 5]; Available from: https://cmuj.cmu.ac.th.

23.

UNSCEAR. UNSCEAR 2000 Report to the General Assembly.
Volume I: Sources. New York: United Nations; 2000.

24.

Kranrod C, Chanyotha S, Pengvanich P, Kritsananuwat R,
Ploykrathok T, Sriploy P, et al. Car-borne sur vey of natural
background gamma radiation in Western, Eastern and Southern
Thailand. Radiat Prot Dosim. 2020;188(2):174–80.

6.

Khamkaew C, Chantara S, Wiriya W. Atmospheric PM2.5 and its
elemental composition from near source and receptor sites during
open burning season in Chiang Mai, Thailand. Int J Environ Sci

34
25.

26.

Chutima Kranrod et al. / Radiation Environment and Medicine 2024 Vol.13, No.1 28–34
Thumvijit T, Chanyotha S, Sriburee S, Hongsriti P, Tapanya M,
Kranrod C, et al. Identifying indoor radon sources in Pa Miang,
Chiang Mai, Thailand. Sci Rep. 2020;10(1):1–14.
Moreley CK, Charusiri P, Watkinson IM. Structural geology ofThailand during the Cenozoic. In: Ridd MF, Barber AJ, Crow MJ,
editors. The Geology of Thailand. London: The Geological Societyof London. 2011. p. 273–334.
27.

Wood SH, Suvagondha Singharajwarapan F, Suvagondha F.
Geothermal systems of Northern Thailand and their association
with faults active during the Quaternary. GRC Trans. 2014;38:607–
15.