We studied the influence of the children's activities, outdoor sources, temperature and relative humidity on particle mass concentrations and particle massesize distribution, and estimate
Trang 1Indoor eoutdoor behavior and sources of size-resolved airborne
particles in French classrooms
Dinh Trinh Trana,*, Laurent Y Allemanb,c, Patrice Coddevilleb,c, Jean-Claude Galloob,c
a Viet Nam National University, Ha Noi, Faculty of Chemistry, 19 Le Thanh Tong Street, Ha Noi, Viet Nam
b Univ Lille Nord de France, F-59000 Lille, France
c Mines Douai, CE, F-59508 Douai, France
a r t i c l e i n f o
Article history:
Received 31 March 2014
Received in revised form
11 June 2014
Accepted 27 June 2014
Available online 5 July 2014
Keywords:
Indoor/outdoor
Particles
Real-time variation
Particle massesize distribution
Cancer risk assessment
a b s t r a c t Indoor and outdoor airborne particles were monitored with a 5-s time resolution in three elementary schools presenting different site typologies (rural, urban, and industrial) in the North of France We studied the influence of the children's activities, outdoor sources, temperature and relative humidity on particle mass concentrations and particle massesize distribution, and estimated cancer risk regarding particle composition
The indoor weekly mean PM10 mass concentrations during teaching hours varied from 70 to
99mg m3, exceeding the French daily recommended value of 50mg m3, implying a potential impact on the respiratory system However,fine particles (<2mm) were always below French daily recommended value of 25mg m3applied to PM2.5
The results showed that children's activities impacted the suspended coarse fraction (2e10mm) more strongly than thefine one (<2mm) The mass distribution of indoor PM10was extremely variable in association with occupant's activities in classrooms whereas the outdoor one seemed to be only lightly variable During lessons, average concentrations of indoor PM1, PM1e2, PM2e5, and PM5e10increased respectively by factors of 2.9, 3.1, 8.7 and 33.8 compared to unoccupied periods
Indoor sources from continuous emission and occupant's activities may lead to lower density of indoor
PM10compared to outdoor ones
The estimation of some potential carcinogen elements such as As, Cd, Cr, and Ni in indoor PM2showed low concentrations in the range of 0.11e1.71 ng m3 Consequently, the cancer risk of these elements was estimated to be not significant for long-term exposure to both children and teachers
© 2014 Elsevier Ltd All rights reserved
1 Introduction
There has been an increasing interest in researches on indoor air
quality of school environment as children spend considerable time
of their school day indoor where, in certain cases, the air is more
polluted than outdoor[1e3] Moreover children are more sensitive
to atmospheric pollutants than adults, due to a non-fully developed
respiratory system and high rates of acute respiratory infections[4]
Many epidemiological surveys have demonstrated that
expo-sure to particulate matter (PM) causes adverse respiratory and
cardiovascular health threats[5e8] Regarding the effect of PM to
children's health, studies showed an association between air
pollution and infant mortality (primarily due to respiratory deaths
in the post-neonatal period), lung function development, and up-per and lower respiratory symptoms[4]
Moreover, the health effects of particles depend strongly on their size, number, morphology, specific surface area, and chemical composition, e.g their heavy metal contents[9,10]
In spite of the fact that researches on indoor air pollution have lagged behind outdoor air, ANSES in France has suggested guideline values of daily PM2.5and PM10concentrations for indoor air, similar
to the WHO guideline for outdoor ones, i.e 25 mg m3 and
50mg m3respectively[11] Moreover, it is generally accepted that prolonged exposure to ultrafine particles can cause adverse health effects[12]
A number of studies on school Indoor Air Quality (IAQ) have focused on respirable suspended particles and their influencing factors (using average mass concentration over a period of time)
[13,14]but only a few have worked both on particulate (size) dis-tribution and real-time variation[15e19]
* Corresponding author.
E-mail addresses: trinhtd@vnu.edu.vn , trinhtdefr@yahoo.fr (D.T Tran).
Contents lists available atScienceDirect
Building and Environment
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / b u i l d e n v
http://dx.doi.org/10.1016/j.buildenv.2014.06.023
0360-1323/© 2014 Elsevier Ltd All rights reserved.
Building and Environment 81 (2014) 183e191
Trang 2Observations and conclusions drawn on indoor particle
con-centrations vary between studies due to the variability of
condi-tions governing the indoor air pollutants such as number of
occupants and/or types of specific activities within the classroom
In addition, sources from educational supplies, school furniture's,
painting and building materials, air renewal rate and outdoor
pollutant sources may also affect the indoor PM content and its
spatial and temporal evolution[3]
The characterization of indoor and/or outdoor sources of
parti-cles collected inside buildings has been already considered in the
literature Most of these works used indoor/outdoor (I/O) ratios and
some employed correlations as basic factors to point out indoor and
outdoor pollution origins[19e22]
Although these approaches reveal details about indoor and
outdoor source relationships, they present some limitations as I/O
ratios or correlations give only general information about the global
pollutant origins, omitting to discriminate each specific source
[1,23]
Recently, some works aimed at identifying the particle origins
using factor analysis[1,3,24] This approach brings richer and more
detailed information about indoor and outdoor pollutant sources
The main purposes of the present paper are to (1) determine the
influence of children's activities on mass concentration of different
particle size fractions, (2) identify the origin of particles collected in
classrooms, and (3) estimate the concentration of some potential
carcinogenic elements and their related cancer risk in a school
environment
2 Materials and methods
During the campaigns performed in three schools, the indoor
and outdoor mass concentrations were monitored in parallel
ac-cording to their particle sizes (PM1, PM1 e2PM2 e5and PM5 e10) along
with meteorological conditions The information about the site
typology and the children's activities in each school during the
whole campaigns has been also recorded by questionnaires
2.1 Sampling sites and school characteristics
The three elementary schools studied are located in the
Nord-Pas-de-Calais region (NPdC, France) near the North Sea coast and
the Belgian border
Sampling sites have been selected to represent different
envi-ronments: industrial and coastal (School 1 e S1), urban/traffic
(School 2e S2) and rural (School 3 e S3) Schools have been also
chosen upon edifice characteristics such as building age, ventilation
system, internal covering includingflooring, wall and ceiling, and
windows structure, as summarized in Tran et al.[3]
The volume of the selected classroom in schools 1, 2, and 3 are
respectively 201 m3, 234 m3and 181 m3 The three schools are
naturally ventilated (by window opening and small cracks as most
schools in France) The number of occupants in each classroom was
rather comparable (from 24 to 27)
2.2 Sampling protocol and statistical analysis
The sampling campaigns lasting continuously for 2 successive
weeks for each school were divided into 2 periods: in presence and
in absence of pupils in the classrooms The occupied period
con-sisted of teaching hours during school days including Monday,
Tuesday, Thursday and Friday Detailed sampling protocol was
re-ported in Tran et al [3] Quickly, the sampling during teaching
hours lasted about 8-h per day (8h45e16h45) while 12-h per day
(from 19 h to 7 h of the next day) were attributed to unoccupied
period including the week-end when the sampling time was
accounted for 24-h per day The sampling campaigns were con-ducted successively in each school from May 13th 2009 to July 1st
2009 under relatively cool and stable meteorological conditions during each campaign (Table 1) Outdoor average temperatures were 15± 2C, 16± 3C and 21± 3C in S1, S2 and S3 respectively
during occupied period and 14± 3c, 13± 3c and 17± 4c during
unoccupied period
Two sets of identical equipments have been deployed indoors and outdoors to measure particulate concentrations, CO, CO2levels, and comfort parameters (temperature, relative humidity) Real-time measurements of indoor and outdoor number concentra-tions of different particulate sizes (15 nominal size bins capturing particles from 0.3mm to 20mm) have been monitored using two pre-calibrated optical particle counter GRIMMS, model 1.108 at 5-s intervals These spectrometers worked by constantly drawing the air sample via a volume controlled pump (1.2 l min1) through aflat laser light beam The particle mass concentration was then ob-tained by conversion from the number concentration measure-ments hypothesizing that the particles are spherical with a density equal to 1 g cm3 Each PM counter was equipped with a 47 mm
teflon filter (Mitex, Millipore) to collect the particles with an optical diameter smaller than 20mm we corrected the reading mass con-centrations obtained by GRIMMs (theoretical values) by weighing these back-upfilters after each school campaign The measurement
of particles mass collected on the filters was conducted in a conditioned room according to EN 12341[3] The reading/weighted value ratio was defined as the correction factor (C-factor) This factor was then used to calculate the adjusted PM10concentrations
it must be noted that the absolute concentrations of PM10 pre-sented in this work are all corrected values
Indoor and outdoor comfort parameters as well as CO, CO2 concentrations were continuously measured using two identical TSI Q-Trak (model 7565 TSI Inc) at 5-s intervals to match the par-ticle mass concentration database Before each campaign, the TSI Q-Trak were calibrated with certified calibration gas (for CO and CO2)
MS Excel and the SPSS 16 statistical package were used for nu-merical evaluation Indoor and outdoor concentrations were compared using the ManneWhitney U test Spearman correlations were conducted to evaluate the relationship between indoor and outdoor mass concentrations A value of p< 0.05 was considered significant in all the statistical calculations
3 Results and discussion 3.1 Indoor and outdoor particle mass concentrations, CO, CO2levels and comfort parameters
Descriptive statistics of different particulate fraction concen-trations (mg m3) as well as CO, CO2 levels, and various comfort parameters during occupied and unoccupied periods are summa-rized inTable 1
The indoor and outdoor CO concentrations were very low (close
to the detection limit) except for a few spike identified as cigarette smoking after the class in yards and corridors This gas was thus excluded from the data base The mean indoor CO2concentrations were remarkably higher during teaching hours than in absence of children, and higher at S1 (712e2900; mean: 1475 ppm) and S2 (406e3488; mean: 1484 ppm) than at S3 (372e2780; mean:
690 ppm) The lowest concentration of CO2during lessons at S3 is clearly associated with the frequent openings of windows and doors in this school (confirmed by the questionnaire), resulting in a higher air exchange with outdoor air The mean values for unoc-cupied periods were respectively 504, 573, and 404 ppm (Table 1) These CO2 levels observed during teaching hours at S1 and S2 regularly exceeded the recommended values[25]and could affect D.T Tran et al / Building and Environment 81 (2014) 183e191
184
Trang 3the student performance during lessons Outdoor CO2levels were
comparable between the three schools at around 350 ppm
As explained in the paragraph 2.2, we used correction factors to
estimate the PM10 mass concentrations in the 3 schools The
C-factors for indoor air at S1, S2, and S3 were respectively 0.67, 0.72,
and 0.75 Note that according to the manufacturer GRIMM, for
outdoor PM, under normal conditions, the C-factor is usually in the
range of 0.8e1.2 and in our case, C-factor outdoor values were
indeed close to unity for the three schools This implies that indoor
PM in this study present a density and/or a refractive index lower
than the PM model (density of approximately 1 g cm3, and
refractive index of about 1.45) used for the GRIMM calibration, and
lower than outdoor ones This could be due to a higher content of
organic compounds than outdoor [26] These compounds could
reflect indoor VOC sources as well, such as paints, construction
materials, wood preservatives, solvents and cleaning products used
each day after school[26,27] The same tendency of higher fraction
of organic compounds indoor than outdoor, (but with variable
ra-tios) was observed for PM2.5[22], and for PM10[28] Inversely, a
larger ion contents (ammonium, sulfates, nitrates…) with a higher
density than organic compound were observed in outdoor PM10
than indoor ones[28] These chemical characteristics could induce
a difference in density that could results in lower C-factor for
in-door PM
In this study, the PM10 fraction comprise particles between
0.3mm and 10mm, a rather good estimate as particles below 0.3mm
represents only a very small portion of total PM10 mass
concen-trations[29] Globally, the corrected PM10concentrations obtained
by the optical counters GRIMM in this paper were comparable
(within 5% in presence of occupants) with those obtained by
gravimetric methods [3] The 8-h average PM10 concentrations
during occupancy were 88.4, 89.3 and 70.0mg m3respectively at
S1, S2, and S3, while in absence of children, the 12-h average PM10
concentrations were respectively 9.3, 21.9, and 11.3mg m3 These
lower concentrations during unoccupied period suggested that
continuous indoor emission sources of PM such as paint, walls or furniture were probably not significant The questionnaire showed that there was no specific source of particle emission as combustion (cooking, household heating, smoking …) during the sampling campaigns at these schools
Outdoor, the PM10concentrations varied from 31.1mg m3(S2)
to 37.8mg m3(S1) during teaching hours and from 16.6mg m3 (S2) to 30.6 mg m3 (S3) when children were out of school Consequently, the presence/absence PM10ratios varied from 3.4 to 5.5 indoors and from 1.3 to 1.8 outdoors, confirming the expected larger impact of human activities in a closed environment These results are comparable with previous studies in classrooms
[16,23,30,31] As indicated in Tran et al [3], we didn'tfind any significant influence due to the specific typology of the schools selected (rural, urban and industrial) on indoor and outdoor PM10
mass concentrations The higher outdoor PM10 concentrations collected at S1 during the occupied period compared to S2 and S3 (Table 1) were attributed to more frequent dust-off of clouts near the outdoor samplers in the courtyard of S1
The number of pupils in the classrooms were comparable (24e27 children), and the volume of the classroom at S3 (181 m3) was slightly smaller than at S1 and S2 (201 m3 and 234 m3, respectively) In absence of large continuous sources of PM beside school activities during teaching hours, this last parameter should favor higher indoor PM10 concentrations at S3 compared to the other schools Yet, indoor PM10 concentrations during teaching hours at S3 were relatively lower than the others This was linked with the fact that the teachers opened frequently the windows and doors at S3 (confirmed by the questionnaire), resulting in a dilution
of indoor air by a much lower content of PM10from fresh ambient air
Based on the feedback form regarding daily activities on site, the usual activities in classrooms were clearly the main sources of in-door PM10as also noted in previous works performed in classrooms
[1,16,23,28,30]
Table 1
Descriptive statistics of size distributed PM concentrations indoor and outdoor, and comfort parameters of the three schools during occupied (8-h of sampling) and unoccupied periods (12-h, values in parentheses) over 2-week campaigns.
0.3e1mg m3 1e2mg m3 2e5mg m3 5e10mg m3 0.3e10mg m3 CO 2 (ppm) T ( C) RH (%) Indoor
S1 Mean 11.2 (2.2) 7.1 (1.8) 59.9 (4.3) 54.4 (1.0) 132 (9.3) 1475 (504) 22.6 (20.9) 50.0 (49.8)
Min 6.7 (1.4) 4.6 (1.1) 35.9 (2.5) 31.1 (0.3) 78.3 (5.8) 712 (377) 19.3 (18.3) 32.1 (37.8) Max 16.9 (3.6) 9.2 (2.6) 94.2 (5.5) 90.4 (2.8) 210 (12.3) 2900 (1054) 25.6 (24.3) 64.3 (66.4) S2 Mean 11.4 (4.8) 6.7 (2.7) 48.4 (9.8) 58.0 (4.6) 124 (21.9) 1484 (573) 18.7 (17.9) 69.6 (64.0)
Min 8.0 (3.4) 4.8 (2.2) 37.5 (7.2) 45.2 (3.4) 95.5 (16.2) 406 (394) 16.7 (16.4) 56.6 (58.5) Max 16.6 (6.3) 10.1 (3.2) 62.3 (14.4) 67.4 (5.8) 156 (28.8) 3488 (1534) 22.3 (20.1) 83.5 (75.5) S3 Mean 14.3 (3.4) 4.8 (1.7) 29.0 (4.0) 41.1 (1.2) 93.3 (11.3) 690 (404) 25.3 (24.3) 46.8 (48.1)
Min 7.4 (3.7) 3.7 (1.1) 20.8 (2.5) 25.7 (0.3) 57.6 (9.8) 372 (357) 21.5 (18.3) 35.8 (25.3) Max 30.8 (4.8) 5.7 (2.5) 35.9 (6.6) 49.1 (2.9) 113 (13.6) 2780 (867) 31.3 (34.7) 77.3 (69.5) Outdoor
S1 Mean 4.3 (4.7) 3.1 (2.4) 14.4 (9.0) 15.9 (5.0) 37.8 (21.1) 357 (336) 15.9 (13.7) 47.0 (60.2)
Min 2.9 (3.8) 1.9 (1.5) 7.9 (6.7) 7.0 (3.6) 28.1 (15.9) 286 (278) 10.8 (8.2) 16.8 (18.8) Max 5.9 (7.7) 4.3 (5.1) 20.4 (16.0) 24.4 (6.3) 54.7 (35.2) 593 (498) 24.0 (21.3) 83.3 (93.5) S2 Mean 4.1 (4.0) 3.6 (2.6) 13.0 (7.1) 10.4 (3.0) 31.1 (16.6) 304 (304) 21.6 (16) 64.4 (75.8)
Min 2.7 (2.4) 2.5 (1.4) 8.6 (4.0) 7.8 (1.8) 22.4 (10.1) 253 (260) 13.3 (8.1) 18.4 (57.3) Max 5.6 (6.2) 6.0 (4.2) 22.5 (10.8) 18.0 (4.9) 44.4 (25.8) 404 (1076) 30.2 (30) 83.4 (97.4) S3 Mean 3.4 (6.4) 3.1 (4.2) 11.4 (14.3) 13.3 (5.7) 32.5 (30.6) 331 (357) 16.5 (12.0) 40.3 (60.8) Std 0.9 (2.6) 0.8 (1.9) 2.5 (7.2) 2.9 (2.3) 7.4 (13.9) 14.0 (65.0) 3.3 (3.1) 18.7 (22.2) Min 2.6 (2.7) 2.4 (1.6) 9.1 (5.4) 11.0 (2.9) 26.0 (12.5) 294 (288) 11.1 (3.6) 10.9 (16.2) Max 4.2 (9.1) 4.1 (6.5) 13.7 (23.3) 17.2 (8.7) 39.9 (47.1) 391 (624) 25.5 (25.6) 84.0 (92.4) Std: standard deviation.
D.T Tran et al / Building and Environment 81 (2014) 183e191 185
Trang 4The PM10values obtained during teaching hours largely
excee-ded the daily limit values (50mg m3) for indoor air (French
rec-ommendations), and were much higher than in absence of children
(Table 1) Outdoor, PM10 concentrations always respected these
daily limit values On the other hand, the smaller PM2 fraction,
often considered more harmful, presented lower concentrations
than the PM2.5 daily limit recommendation from France
(25mg m3), both indoor and outdoor
3.2 Indoor and outdoor particle massesize distribution
The relative percentages of different size fractions of indoor and
outdoor PM10at S1, S2, and S3 are shown inFigs 1 and 2
Outdoors, the percentages of PM1, PM1e2, PM2e5, and PM5e10
during teaching hours were comparable and varied only slightly
from school to school These small variations might be associated
with emission processes and/or the proximity of sources which
could modify the particle size distribution[32] In addition, the
children's activities in the school's yards during breaks could also
influence the mass distribution of outdoor PM10by adding up to the
coarser fractions However, this phenomenon was partially masked
by the dilution of ambient air over weekly period probably
explaining why we did not observe much variation in outdoor PM10
concentrations During unoccupied period, the tendency was
almost alike but with a decrease of the PM5 e10 fraction and a
symmetrical increase of thefiner fractions (Fig 1) Indeed, the PM1,
PM1e2, PM2e5, and PM5e10 accounted respectively for 10e13%,
8e11%, 35e41%, and 33.4e42% of the total PM10mass
concentra-tions during teaching hours When schools were vacant, these
values were respectively 21e24%, 11e15%, 42e46%, and 18e23%
Indoors, the mass distributions variability of PM1, PM1 e2, PM2 e5,
and PM5e10at S1, S2, and S3 were more remarkable In presence of
pupils in the classrooms, the coarse fraction PM2e10made up most
part of the total mass of PM10 For instance, this fraction accounted
for 86% (S1 and S2), and 75% (S3) of PM10(Fig 2) On the contrary, in
absence of children, there was a sharp drop of the coarse fractions,
in particular the PM5 e10fraction Indeed, this last fraction
repre-sented 41.2e46.8% of PM10 during the teaching hours, but only
about 10% (S1 and S3), and 21% (S2) in absence of pupils Inversely,
an increase of thefine fractions was observed from the occupied to
the unoccupied period, PM1accounting for about 9% (S1 and S2)
and 19% (S3) during teaching hours and rising up to about 23% (S1
and S2) and 39% (S3) during unoccupied period (Table 1) These
results imply that the presence of occupants and their activities in
classrooms are at the origin of the coarse particles increase In absence of occupants and other significant emission sources of PM
in the classrooms, the relativefine fractions drastically increase in the indoor environment Similar observations on the impact of occupants' activities indoors on coarse fractions were also reported
in previous works[16,18,23,30] Interestingly, the relative percentage of the PM1was higher at S3 than at S1 and S2, both during teaching hours or vacant periods These observations are again linked to the large openings of doors and windows during occupied period at S3 while doors and win-dows were systematically closed at S1 and S2 Moreover, the air-tightness at S3 was lower than at S1 and S2 due to cracks on the walls and around the windows and doors, resulting in a much higher air exchange rate (estimated values by the CO2 decay method are about 5 times higher at S3 than at S1 and S2 during unoccupied period) Consequently, a higher air exchange rate could promote a quicker dilution of the indoor coarse fraction by outdoor air without influencing significantly the fine particles presenting similar indoor and outdoor concentrations
3.3 Real-time variation of indoor and outdoor particles The real-time variation of indoor and outdoor PM concentra-tions combined with questionnaires information about teaching activities allowed us to interpret their relative influence with time
As a case of study, we only present here the indoor and outdoorfine and coarse particles variations during 2 consecutive weeks at S1 (Figs 3 and 4) Indeed, similar tendencies were evidenced at S2 and S3; and while S1 presented a complete dataset, the others had some missing data due to power outage at S2 and to instrumental breakdown at S3
In this paragraph, we grouped the fractions PM2e5and PM5e10 into the so called coarse fraction PM2 e10as they showed similar
behaviors For the same reasons, the PM1and PM1 e2were grouped
to represent thefine fraction PM2
As shown inFig 3, during the class, the mass concentration of indoor PM2 was slightly higher than that measured outdoor whereas in absence of occupants in the classrooms, it was the opposite The evolution of indoorfine particles did not seem to be correlated to outdoor ones It was also observed some relatively small spikes of this size fraction We associated them with occu-pant's activities in classrooms (walking, sitting, and playing), given that during school days, the doors and windows were sometime kept open which should have lead to similar concentrations indoor
Fig 1 Outdoor particle size-distribution during occupied and unoccupied periods.
PM 10 (mg m3) ¼ 37.8; 31.1; 32.5 for S1; S2; S3 during occupied period and ¼ 21.1; 16.6;
Fig 2 Indoor particle size-distribution during occupied and unoccupied periods PM 10
inmg m3¼ 132; 124; 93.3 for S1; S2; S3 during occupied period and ¼ 9.3; 21.9; 11.3 during unoccupied period, respectively.
D.T Tran et al / Building and Environment 81 (2014) 183e191 186
Trang 5and outdoor The larger spikes were linked to sweeping activities
on thefloor at the end of the school day
The variation of indoor concentrations of the coarse fraction
(PM2e10) related to occupant's activities in classrooms was more
noteworthy (Fig 4) Indeed, this size fraction increased sharply as
soon as the arrival of occupants (at about 8h40 AM) and phased out
quickly during both the breaks (at about 10h30 and 15h00) and the
lunch time (11h45e13h45) in weekdays (Fig 5) The most intense
spikes of PM2 e10concentrations were observed during the cleaning
routine after the class This type of activity could result in an
in-crease of 50e70 times the indoor PM2 e10concentrations compared
to unoccupied period
Outdoor, the variation of this fraction was not as significant and sometimes was anti-correlated with indoor ones, particularly during the breaks and lunch time when the pupils played in the courtyards and close to the monitoring instruments
3.4 Indoor/outdoor mass concentration ratios (I/O) This paragraph evidences the integrative impacts of different phenomenon such as the children's activities in the classroom, the outdoor PM concentrations or the building air permeability on I/O ratios for different particulate size fractions The results are re-ported inFigs 6 and 7 Note that the time-resolution data was used
Fig 3 Indoor and outdoor real-time variation of fine particle PM 2 at S1 over a 2-week period.
Fig 4 Indoor and outdoor real-time variation of coarse particles at S1 over a 2-week period.
D.T Tran et al / Building and Environment 81 (2014) 183e191 187
Trang 6to calculate the average particle concentrations for both occupied
and vacant periods
The Mann and Whitney U test show significant I/O ratio
differ-ences between presence and absence of children at p< 0.001 for
PM2and PM2 e10(Figs 6 and 7) whilst this ratio is comparable for
submicron particles PM1
In presence of occupants, I/O ratios of the coarse fraction PM2e10
were comprised between 7.0 and 9.6 at S1, S2, and S3 These values
for thefine fraction PM2were much lower and closer to 1, implying
the presence of indoor sources regarding the coarse fraction (Fig 6)
These indoor sources were undoubtedly associated to children's
activities in classrooms which could emit PM directly with their
clothes, shoes, hair, and indirectly by the resuspension of
previ-ously deposited PM [33e36] The utilization of chalks during
teaching hours could also introduce an important source of coarse
PM[3,37]
In absence of occupants (evenings, nights, and week-ends), the
I/O ratios of all the particulate fractions were below 1, linked
probably to (1) the absence or negligible continuous indoor
sour-ces, (2) the particlefiltration efficiency of the building envelope
[24,35,36,38e40], and (3) the higher indoor deposition factors than outdoor due to the larger indoor surface/volume ratio[41] Note that I/O ratios of the different size fractions at S3 were always lower than at S1 and S2 (Fig 7) This may seem contradic-tory with a higher air exchange rate at S3 In other words, S3 should present a higher penetration of outdoor PM into the classrooms resulting in higher I/O ratios at S3 (closer to one) during unoccu-pied period That was probably linked to an artifact associated to our sampling strategy Actually, the measurements performed during unoccupied period started about 2 h after the departure of the children when the PM concentrations in indoor air could still be relatively high, particularly the days when the cleaner swept the floors, increasing de facto the I/O ratios At S3 (rural school), the doors were opened directly to the courtyard after class, allowing a rapid equilibrium between indoor and outdoor PM which limited the above-mentioned bias By contrast, at S1 and S2, the doors were only opened to the corridors, resulting in a lower air exchange with outdoor and then in a slower decrease of the coarse fractions This bias was eliminated when integrating the sampling time from midnight to the next day up to the arrival of children in the Fig 5 Zoom on real-time variation of indoor coarse particles during teaching hours (June 8th 2009) at S1.
Fig 6 I/O ratios of different size fraction during occupied period (n ¼ 8, 6 and 4 at S1, Fig 7 I/O ratios of different size fraction during unoccupied periods (n ¼ 8, 6 and 4 at
D.T Tran et al / Building and Environment 81 (2014) 183e191 188
Trang 7classrooms (to make sure that most suspended particles were
deposited) By doing so, we found that the I/O ratios of different size
fractions were slightly higher at S3 compared to the other, but still
lower than 1 Indeed, the average I/O ratios for PM2at S1 and S2
were about 0.30 against ~0.4 at S3 The corresponding values for
PM2 e10at S1 and S2 were 0.18 against 0.2 at S3 We demonstrate
here that when dealing with I/O ratios, one should carefully
consider the time resolution and sampling periods to avoid such
artifacts
3.5 Contribution of PM emitted during occupied period to the
indoor PM sampled during unoccupied period
The class ended generally at 16h30 every school's day
fol-lowed, 15e30 min after the departure of the children, by dusting
(twice a week), and sweeping/wet cleaning with detergents
(twice a week) the classrooms The dusting/cleaning lasted
generally about 30 min, the cleaner leaving the classroom at
about 17h00e17h15 The movement of the occupants at the end
of the class as well as the vigorous sweeping activities resulted in
the suspension of a large amount of PM previously deposited on
the indoor surfaces (particularly on the floor) since the last
cleaning In addition, the use of detergents for cleaning could
result in formation of new particles such as secondary organic
aerosols[42] The high PM concentrations due to these activities
could modify the indoor particles behavior during unoccupied
period (Table 2) To examine this phenomenon, we calculated the
percentage of PM sampled from 19h00 (about 2 h after the
de-parture of the cleaner) to 23h00 against the total PM sampled
during the whole night from 19h00e7h00 the next day (Table 2)
Based on the PM concentration decrease after the departure of
occupants, the 23h00 cap was set to make sure that most of the
fine and coarse PM previously suspended were quantitatively
deposited on thefloor
As shown inTable 2, the average mass of PM2sampled during
thefirst third of the sampling period (19h00e23h00) at S1 and S2
accounted for 62% and 55% of the total PM2collected during the
whole night (from 19h00e7h00, the next day) These values for the
PM2e10fraction were significantly higher with 84% and 80% for S1
and S2, respectively We can assume that the indoor PM
concen-trations present a rather constant decrease during the whole
un-occupied period with a relative steady penetration of outdoor PM
and a similar deposition velocity (classrooms closed and no
sig-nificant indoor emission sources) Although this hypothesis may be
questionable in terms of coagulation phenomenon and deposition
rate, this rough assumption may help us to estimate the impact of
the resuspension fraction Theoretically, the PM2 e10sampled from
19h00e23h00 should represent about 33% of the total PM2e10
sampled during the whole unoccupied period The same
percent-age should be found for the PM2fraction
By subtracting the theoretical concentration (33% for the three
schools) from the measured concentrations, we found that 51% (for
S1) and 47% (for S2) of the PM2 e10resuspended during occupied
period were accounted for unoccupied period These values for the
PM2were 29% and 22%, respectively for S1 and S2, confirming again
the larger influence of children's activities to the suspension of the
coarse fractions
It is interesting to note that at S3, the coarse and fine PM sampled from 19h00e23h00 accounted for only one third of their total mass sampled during the whole unoccupied period (Table 2), matching the theoretical values and suggesting negligible impact of the sweeping activities in this school This is in agreement with the strong air exchange rate during and after the teaching hours resulting in a fast wash out of indoor PM by a cleaner outdoor air and in a quick ex-filtration of indoor PM
3.6 Heavy metal concentrations in classrooms and their risk assessment
In this section, we reviewed the concentration of four elements (As, Cd, Cr, and Ni) defined as carcinogens (Group 1) by the Inter-national Agency for Research on Cancer (IARC) in the PM2as they can reach the pulmonary alveoli and even penetrate into the bloodstream[43] Then, we estimated their potential risk during teaching hours at S1 situated in an industrial zone To do so, we considered that the relative concentrations of these elements in indoor PM do not change significantly during occupied period or from day to day
The concentration of As, Cd, Cr, and Ni were calculated using mass concentration of PM2 obtained by GRIMM measurements during teaching hours multiplied by the percentage of these ele-ments in the PM2.5reported in a previous work[3] Consequently, the percentage of As, Cd, Cr, and Ni in the PM2.5may slightly differ from PM2discussed in this paper, somehow compensated by the missing fraction from the GRIMM, unable to measure particles below 0.3mm
As shown inTable 3, concentrations for As, Cd, Cr, and Ni were calculated respectively at 0.46± 0.11 (ng.m3), 0.11± 0.03 (ng.m3), 1.27± 0.30 (ng.m3), and 1.71± 0.40 (ng.m3) These values are
relatively higher than that of S2 and S3 (results not shown here) They are 3 times (for As) to more than 10 times (for Ni) higher compared to the concentrations of these elements measured in 39 schools in Barcelona[44], although Cd concentrations are compa-rable However, the concentrations of Ni and Cr were comparable with the work of Molnar et al.[45]conducted duringfive schools in Stockholm, Sweden
Regarding the risk assessment, we used the incremental cancer risk factor as described in Feng et al.[46]considering a period of five years (number of years that children study in an elementary school) It can be calculated by multiplying the cancer potency factor of a given carcinogen with the chronic daily intake (CDI) The cancer potency factors of As, Cd, Cr, and Ni are 15; 6.3; 41; and 0.84 (mg/kg/day), respectively The CDI is calculated using the following equation
Table 2 The percentage of PM sampled from 19h00e23h00 compared to the PM sampled during the whole unoccupied period (sampling from 19h00e07h00 the next day) Percentage of PM 2
and PM2e10(%)
Schools (n: Number of nights) S1 (n ¼ 8) S2 (n ¼ 6) S3 (n ¼ 5)
CDIðmg=kg=dayÞ ¼C mg
m3
$Intake rate m3
day
$Exposureðdays=studied periodÞ Body weightðkgÞ$5$ðy=studied periodÞ$365ðdays=yÞ
D.T Tran et al / Building and Environment 81 (2014) 183e191 189
Trang 8where, C is the concentration of the studied element in the indoor
air, and intake rate is the amount of air that a child inhaled each day
for the studied period offive years
According to the EPA[47], children in elementary schools aged
from 6 to 11 years have an average body weight of 31.8 kg For an
average intensity of activities during teaching hours including
seating, playing, running, their inhalation rate is estimated at
1.32 m3h1[47] In this work, the teaching hours start at 08h45 and
end at 16h45 with a break of 1h30 for lunch The exposed time of
children to indoor PM is therefore estimated at 6.5 (h) The average
volume of air inhaled by a pupil during occupied period (one school
day) will therefore be 8.58 m3 In addition, in France, the children
work normally 9 months/year and 4 days/week
The estimated incremental cancer risk factor for As, Cd, Cr, and
Ni were respectively 0.74$106; 0.07$106; 5.55$106, and
0.15$106 These values, except for Cr, are lower than the limit that
is usually set at 1 106corresponding to a life time exposure to
unpolluted ambient environment[46] This implies low cancer risk
regarding these elements in classrooms
However, the cancer risks calculated for the children in the
above-equation in this section only takes into account 6.5 h/day,
4 days/week, and 9 months/year of time exposure to air containing
these trace elements representing only a small fraction of their real
total exposure (~11%) If we consider that the concentrations of As,
Cd, Cr, and Ni in the classrooms are similar to other indoor
envi-ronments where children are present (home, transport facilities…)
and they spent 80% of their time indoor, the cancer risks regarding
these elements will be respectively 1.50$106; 0.15$106; 11.3$106;
0.31$106 These values are above (for As and Cr), or lower than the
limit 1 106(for Cd and Ni) However, when considering the
bioavailable form that permits to more accurately assess the
envi-ronmental and health risks, the cancer risk factor could decrease
significantly (about 10 times for Cr) according to Feng et al.[46]
This suggests little cancer risk for the 4 studied elements when
using their bioavailable form in the PM2in school environment
Teachers spent more time in the classrooms during their active
life than children leading to longer exposure to indoor PM
con-taining heavy metals As, Cd, Cr, and Ni Nevertheless, calculated
values of cancer risk regarding As, Cd, Cr, and Ni in the indoor PM2for
teachers were comparable with that of children, assuming
param-eters for a teacher as follow: 65 kg of body weight, 20 m3of inhaled
air/day for 38 years of carrier and a life expectancy of 75 years
Finally, in this study we focused on the estimation of cancer risk
regarding thefine fraction PM2 while occupants inhale also the
coarse PM2 e10presenting higher concentrations in the classrooms.
Indeed, this coarse fraction may ultimately be removed from the
pulmonary system by the mucociliary clearance, then swallowed
and digested, freeing pollutants to the systemic circulatory system
This may represent a supplementary effect to cancer risk
assess-ment that should be accounted for in future works
4 Conclusions and perspectives
This paper demonstrated the influence of children's activities in
the classrooms on the indoor coarse andfine particles behaviors
During teaching hours, when there were intense activities, the
PM10 concentrations in the classrooms of the 3 schools were significantly higher than the daily recommendation values ac-cording to French standards that could cause health problems on the fragile children respiratory systems The occupant's activities impacted essentially the coarse fractions whereas in absence of activities, thefine fraction became more important in the air Regarding occupied period, indoor PM fate and sources were primarily associated to occupant's activities whereas during un-occupied period, these behaviors and sources were still strongly
influenced by the PM resuspended during teaching hours, many hours after the class More generally, the influence of the occu-pant's activities may overcome various continuous indoor sources
as well as the impact of the building permeability on the indoor
PM concentrations The PM emitted by pupil's during occupied periods as well as cleaning activities after the class could account for up to 50% for the coarse PM and 30% for thefine ones sampled during unoccupied period Consequently, attention to this phe-nomenon should be paid when one want to study the dynamic
of particles or more generally the air quality of an indoor environment
The occupant's activities in the classroom might also result in the higher organic fraction in PM10than outdoor ones which favor
in return the low density of indoor PM10 Regarding some potential carcinogen elements such as As, Cd,
Cr, and Ni in the indoor PM2, the estimated results showed that the cancer risk associated with these elements was not significant for children except for Cr Moreover, taking into account a time expo-sure in other indoor environment and considering the bioavailable fraction of these metals, both children and teachers spending a lot
of time in classroom during their career present very low risk of cancer due to PM2inhalation
It would be pertinent to quantify both the global contribution of all emission sources as well as each independent source to the coarse andfine PM concentrations during the teaching hours by looking at a large variety of organic and inorganic compounds In addition, this information along with parameters of particle dy-namic in indoor air such as penetration capacity, deposition ve-locity and air exchange rate may allow one to estimate the real-time exposure of children to indoor PM and therefore to study the in-fluence of specific indoor sources on children's health
Acknowledgment This research project was part of the“Institut de Recherche en Environnement Industriel” (IRENI) and was financially supported
by the Nord-Pas-de-Calais Regional Council (Program IRENI, Action
1, Axe 1& 2 e Convention ANR 2006 e Action regionale e CPER DT
n15006e Decision n06e CPER n093-01e Convention FEDER, Obj 1 e 2006/3 e 4.1 n 79/8559 (2006e2008)), by the French Ministry of Higher Education and Research, by the European Regional Development Funds (through the Regional Delegation for Research and Technology) and Mines Douai-Armines Research Centre We thank Bruno Malet for its valuable and continuous technical support
Table 3
Estimated concentration of As, Cd, Cr, and Ni for indoor PM 2 at S1 (n ¼ 8) and their incremental cancer risk for a period of five years.
Elements Mean ± Std
(ng/m 3 )
Median (ng/m 3 ) Min (ng/m 3 ) Max (ng/m 3 ) Cancer potency
factor (mg/kg/day)
CDI for 5 years (mg/kg/day)
Incremental cancer risk for 5 years
D.T Tran et al / Building and Environment 81 (2014) 183e191 190
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