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Journal of Hazardous Materials 289 (2015) 184–189
Contents lists available at ScienceDirect
Journal of Hazardous Materials
jo ur nal ho me p ag e: www.elsev ier .com/ locate / jhazmat
evelopment of an activated carbon filter to remove NO2 and HONOn indoor air
un Young Yoo a, Chan Jung Park b, Ki Yeong Kim c, Youn-Suk Son d,∗, Choong-Min Kang e,ack M. Wolfson e, In-Ha Jung d, Sung-Joo Lee d, Petros Koutrakis e
Air Development Group, Coway R&D Center, Seoul National University Research Park, 56-39, Nakseongdaero 15-gil, Gwanak-gu, Seoul 151-919, SouthoreaDevelopment Division, Coway R&D Center, Seoul National University Research Park, 56-39, Nakseongdaero 15-gil, Gwanak-gu, Seoul 151-919, SouthoreaR&D Center, 3AC Co., Ltd., 1521-3, Sicheong-ro, Bongdam-eup, Hwaseong-si, Gyeonggi-do 445-902, South KoreaResearch Division for Industry & Environment, Korea Atomic Energy Research Institute, Jeongeup-si, Jeollabuk-do 580-185, South KoreaExposure, Epidemiology, and Risk Program, Department of Environmental Health, Harvard School of Public Health, 401 Park Drive, Landmark Center Westoom 417, Boston, Massachusetts 02115, United States
i g h l i g h t s
This study developed an activatedcarbon to simultaneously removeboth NO2 and HONO.We investigated various factors(loading rate, metal precursors, andmixture ratios).NO2 and HONO could be efficientlyremoved by an improved activatedcarbon filter that was impregnatedwith two types of compounds (2.5%PABA + 6% H3PO4 and 3% KOH).
g r a p h i c a l a b s t r a c t
r t i c l e i n f o
rticle history:eceived 18 September 2014eceived in revised form 14 January 2015ccepted 13 February 2015vailable online 16 February 2015
eywords:
a b s t r a c t
To obtain the optimum removal efficiency of NO2 and HONO by coated activated carbon (ACs), the influ-encing factors, including the loading rate, metal and non-metal precursors, and mixture ratios, wereinvestigated. The NOx removal efficiency (RE) for K, with the same loading (1.0 wt.%), was generallyhigher than for those loaded with Cu or Mn. The RE of NO2 was also higher when KOH was used as the Kprecursor, compared to other K precursors (KI, KNO3, and KMnO4). In addition, the REs by the ACs loadedwith K were approximately 38–55% higher than those by uncoated ACs. Overall, the REs (above 95%) of
ONOO2
ndoor airctivated carbon filterir cleaner
AQ
HONO and NOx with 3% KOH were the highest of the coated AC filters that were tested. Additionally,the REs of NOx and HONO usinKOH) were the highest of all tshow that AC loaded with variin indoor air.
∗ Corresponding author at: Research Division for Industry & Environment, Korea Atomepublic of Korea. Tel.: +82 63 570 3345; fax: +82 63 570 3347.
E-mail address: [email protected] (Y.-S. Son).
ttp://dx.doi.org/10.1016/j.jhazmat.2015.02.038304-3894/© 2015 Elsevier B.V. All rights reserved.
g a mixing ratio of 6 (2.5% PABA (p-aminobenzoic acid) + 6% H3PO4):4 (3%
he coatings tested (both metal and non-metal). The results of this studyous coatings has the potential to effectively reduce NO2 and HONO levels© 2015 Elsevier B.V. All rights reserved.
ic Energy Research Institute, 29 Geumgu-gil, Jeongeup-si, Jeollabuk-do 580-185,
dous Materials 289 (2015) 184–189 185
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J.Y. Yoo et al. / Journal of Hazar
. Introduction
There is growing concern about indoor air quality (IAQ) sinceecent researches have reported that indoor levels for certain pol-utants could be higher than the corresponding outdoors [1,2].ccording to U.S. Environmental Protection Agency (EPA), theverage time that US citizens spend daily in different microen-ironments (including vehicles) is 22.3 h [3]. In Germany, theerman Environmental Survey 1990/1992 (GerES II) found that
his duration was 20.9 h [4]. In Korea, the time spent indoors dur-ng weekdays and weekends were 16.0 and 17.8 h, respectively [5].herefore, indoor air quality has been recognized as a pivotal factor
n determining health and welfare [6,7].The nitrogen dioxide (NO2) and nitrous acid (HONO) found in
ndoor air are generated from various sources. Indoor sources ofO2 include indoor combustion, tobacco smoking, and infiltration
rom outdoors [8]. For HONO, two sources are well known: directmissions from the combustion processes; and heterogeneouseaction of NO2 with water vapor on indoor surfaces [9–11]. Indooroncentrations of NO2 and HONO vary significantly. The 24-h aver-ges of NO2 and HONO were 8–209 ppb and 0–42 ppb, respectively,epending on environmental factors such as the ventilation rate,urning time, and the source and strength of combustion [8,10–17].urthermore, Brauer et al. [12] found in their study that peakoncentrations of indoor NO2 and HONO were 955 and 106 ppb,espectively. Indoor exposure of NO2 and HONO could also be moreroblematic because their high levels can persist for longer timeshan in outdoor air [11].
NO2 and HONO have direct and indirect adverse health effects.ong-term exposure to NO2 is associated with increased suscepti-ility to lower respiratory tract illness [18–20]. Meng et al. reportedhat NO2 was associated with increased risk of chronic obstruc-ive pulmonary disease mortality [21]. In acute and chronic animalxposure tests, mice exposed to NO2 experienced greater mortalityrom induced bacterial or viral infections than mice not exposed toO2 [18,22–24]. In addition, NO2 exposure is a potential inducer ofeurological diseases [25]. It has been reported that HONO could be
nvolved in the formation of carcinogenic nitrosamines [26]. HONOould also affect mucous membranes and lung function [27,28].
A number of air cleaning technologies have been developed andsed to improve indoor air quality. While Paulin et al. [29] reportedhat the installation of a ventilation hood over an existing gas stoveould not improve indoor NO2 levels in urban homes, they foundhat the placement of air purifiers with HEPA and carbon filtersould decrease indoor NO2 concentrations. Adsorption of gaseousollutants by activated carbon (AC) is, in general, highly effectiveecause of a high surface area and micro-porous structure [30–32].
n addition, both laboratory and field studies have been conductedo evaluate the effectiveness of air cleaners for the reduction ofOx in indoor air [32–34]. However, to the best of our knowledge,o previous studies on removing HONO from indoor environmentsave been carried out. Thus, further development of efficient andppropriate methods to simultaneously remove NO2 and HONOs needed because these are among the many air pollutants thatxist in real indoor environments. In addition, the removal efficien-ies (REs) for individual gaseous pollutants are remarkably differentased on the characteristics of ACs and the loading materials. Thiseans that we need more studies to complement the increase of
he RE by the kind of target compound when we select an AC.The aim of this study was the development of an AC filter to
emove both NO2 and HONO. To do this, we tested ACs loaded with variety of metals and non-metals to assess their REs. We also
nvestigated various influencing factors including the loading ratend precursors of metals to obtain optimal REs of indoor NO2 andONO. Additionally, to apply in a real indoor environment, wherearious gaseous pollutants such odorous and/or volatile organicFig. 1. Variations of NO, NO2, and NOx concentrations in the chamber with respectto elapsed time.
compounds exist, we conducted a study of REs through the mixtureratios with ACs.
2. Materials and methods
2.1. Generation of gaseous NO2 and HONO
In this study, nitric acid (60 ml, EP grade 60–62%) and a copperbar (size: 27 × 90 × 3 mm) were used to generate NO2 as follows.
Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Two glass bottles were placed in a glove box inside an air-tight chamber. One glass container was filled with nitric acid andanother glass had a copper bar in water. Each glass container wasequipped with a cap to prevent vaporization into air. To generateNO2, both glass bottles were opened and the copper bar was thenimmersed in the nitric acid. At that time, the NO2 concentrationin a chamber was continuously monitored by a chemilumines-cence NO/NO2/NOx analyzer (T200, Teledyne Advanced PollutionInstrumentation, USA) in order to achieve an appropriate ini-tial concentration. When the NO2 concentration in the chamberreached the target level, the copper bar was moved into the glasscontainer filled with water, and the caps of both containers wereclosed. Then, to obtain a sufficient and stable HONO level througha reaction with NO2 formed in the chamber (by wall reactions ofNO2 and water) [11,35], the air in the chamber was mixed by fansfor 1 h. The initial concentrations of NO2 and HONO formed were10 ± 2 ppm and 1 ± 0.2 ppm, respectively.
2NO2 + H2O ↔ HONO + HNO3
2.2. Chambers and air cleaner
To estimate the emission and removal rates of air pollutants inindoors, various exposure chamber systems have been designedand used [36–38].
A pilot-scale acrylic chamber with a volume of 1 m3 was made toexamine the temporal variability of the generated NO2 and HONOconcentrations. As shown in Fig. 1, after an initial reaction timeof 10 min, NOx concentrations (as a surrogate of NO2 plus HONO)remained stable for at least 1 h. This stability was due to the rel-atively low removal rate of NO, NO2, and NOx by adsorption onthe chamber surface and decomposition reactions: 1.2, 7.1, and4.9%, respectively. Temperature and humidity in the chamber were
◦
maintained at 15–20 C and 40–50%, respectively. A small custom-made air cleaner was located inside the chamber. This air cleanerconsisted of a 2.5 m3/min fan (FD 1238A 2HS, F&F, China) and anAC filter (30.0 g inside a holder, size 120 × 120 × 10 mm).
186 J.Y. Yoo et al. / Journal of Hazardous M
Tab
le
1Su
mm
ary
of
imp
regn
ated
met
als
and
thei
r
char
acte
rist
ics.
Met
al
Ch
arac
teri
stic
s
of
met
al
pre
curs
or
Nam
e
Mol
ecu
lar
wei
ght
of
met
alM
etal
con
ten
t
(%)
Nam
e
Mol
ecu
lar
form
ula
CA
S
Mol
ecu
lar
wei
ght
of
pre
curs
orM
elti
ng
poi
nt
(◦ C)
Boi
lin
g
poi
nt
(◦ C)
Solu
bili
ty
in
wat
er
Cu
63.5
46
3.00
Cop
per
(II)
nit
rate
trih
ydra
teC
u(N
O3) 2
·3H
2O
1003
1-43
-3
241.
60
114
170
(dec
omp
oses
)13
7.8
g/10
0
mL
(0◦ C
)2.
00M
n
54.9
38
2.00
Man
gan
ese(
II)
acet
ate
tetr
ahyd
rate
Mn
(CH
3C
OO
) 2·4
H2O
6156
-78-
1
245.
09
80So
lubl
e1.
33K
39.0
981.
00Po
tass
ium
iod
ide
KI
7681
-11-
0
166.
00
681
1330
128
g/10
0
mL
(0◦ C
)Po
tass
ium
hyd
roxi
de
KO
H
1310
-25-
3
56.1
1
406
1327
97
g/10
0
mL
(0◦ C
)Po
tass
ium
nit
rate
KN
O3
7757
-79-
1
101.
10
334
400(
dec
omp
oses
)
13.3
g/10
0
mL
(0◦ C
)Po
tass
ium
per
man
gan
ate
KM
nO
4
7722
-64-
7
158.
03
240
(dec
omp
oses
)
6.4
g/10
0
mL
(0◦ C
)
aterials 289 (2015) 184–189
Based on the lab-scale chamber experiments, a pilot-scalechamber (4 m3) was built to estimate the REs of NO2 and HONOusing selected ACs for this study. A fan was installed to circulateair to achieve uniform concentrations of NO2 and HONO through-out the chamber. An air cleaner equipped with an AC filter (200 g,size 377 × 297 × 10 mm) was located at the center of the chamber.After the stabilizing time, the mixing fan was turned off, and the aircleaner was turned on remotely to remove NO2 and HONO in thechamber.
2.3. Measurement of NO2 and HONO
In order to measure the concentrations of NO2 and NO, a gassampling pump set (GV-100S, GASTEC, Japan) and two types ofdetection tubes (No. 9L for NO2 and No. 10 for NO, GASTEC, Japan)were used. The tube minimum detection limits provided by themanufacturer were 0.1 and 1 ppm for NO2 and NO, respectively.
Additionally, to measure continuous NO2 and HONO concen-trations, we modified the previous method by Beckett et al.[27]. A chemiluminescence NO/NO2/NOx analyzer (T200, TeledyneAdvanced Pollution Instrumentation, USA) with a system consistingof one switching valve and two filters packs was used in this study.One filter pack was equipped with a polyurethane filter coated withsodium carbonate to remove HONO in the sample air, and the otherfilter pack was equipped with an uncoated filter. These two fil-ter packs were installed in parallel to the analyzer inlet and theswitching valve was used to change the sample channel from onefilter pack to the other filter pack every 3 min. The HONO concen-tration was determined as the difference of HONO concentrationsdownstream the coated and uncoated filters. All removal efficien-cies (REs) of ACs were determined through triplicate experiments,for which the relative standard deviations were <3%. At this time,the standard deviations under all experiment conditions in thisstudy were <2% (RE).
2.3. Preparation of adsorbents
A variety of ACs and metals was tested to obtain the optimalREs. First, four commercial ACs (referred to as AC-1, AC-2, AC-3 and AC-4; these ACs are now used in air cleaners sold fromKorean market) were constructed with 3 mm (thickness) and theninstalled in the air cleaner. As shown in Table 1, different metals,including K [KI, KOH, KNO3 and KMnO4], Cu [Cu(NO3)2·3H2O], Mn[Mn(CH3COO)2·4H2O)] were loaded on the surface of the AC. Atthis time, two other kind of ACs, such as JEC (Japan EnviroChemi-cals, Japan) and 3T-BFU (Kuraray Chemical Co., Ltd.), were also usedto load various metals. A dipping method was used to impregnatemetals on the surface of the AC. Each AC was dipped in the watersolutions of each metal precursor for 2 h, and the AC was then dehy-drated in a convection oven at 150 ◦C (except KOH – at 120 ◦C) over8 h. The losses by the drying process were estimated to be less than1.0%. The ACs impregnated with metals were kept in sealed contain-ers to prevent moisture adsorption and contamination from gases(by diffusion) in room air.
3. Results and discussion
3.1. Commercial activated carbons
Generally, ACs in an air cleaner are used to remove variousgaseous compounds (such as NO2 and volatile organic compounds)indoors. Additionally, to enhance the REs of these compounds, some
ACs are also reformed by several types of processing. Therefore,above all, the performance test of the ACs used in commercial aircleaners was conducted to compare with the REs of the AC devel-oped through this study.
J.Y. Yoo et al. / Journal of Hazardous M
Fv
ATswAtctrlAiafwrsmi
3
ppmt(t[bOc
experiment
Further tests were conducted using a pilot-scale chamber witha volume of 4 m3. The initial concentrations of NOx and HONO
ig. 2. Removal efficiency of NOx with respect to four commercially available acti-ated carbons used in the air cleaner.
We assessed the removal efficiencies of NOx using four differentCs (referred to AC-1, AC-2, AC-3, and AC-4) used in an air cleaner.he initial NOx concentration used was approximately 10 ppm. Ashown in Fig. 2, the REs by all commercial ACs tended to increaseith the passage of time. For the four types tested, AC-1, AC-2,C-3, and AC-4, the REs (%; (1 − C/C0) × 100; C0 = initial concentra-
ion of a target compound; C = residual concentration of a targetompounds after 30 min) of NOx were 65, 75, 34, and 63%, respec-ively. The trends of REs by AC-2 and AC-4 were similar, showingelatively sharp increases during the initial 5 min, and graduallyeveling off afterwards. In contrast to AC-2 and AC-4, the REs byC-1 and AC-3 did not increase significantly after 20 min, indicat-
ng that the ACs reached a steady state. In general, the RE increasess the specific surface area of AC increases [39]. The specific sur-ace areas measured by the Brunauer–Emmett–Teller (BET) method
ere 786, 782, 900 and 926 m2/g for AC-1, AC-2, AC-3 and AC-4,espectively. Our results are not consistent with those of previoustudies [34,39–41]. It is possible some metals (or other coatings)ay have been already impregnated on the commercial ACs to
mprove the RE of the gases.
.2. Impact of impregnated metals
Transition metals (such as Cu, Mn, and Ni) and K have been usedreviously to impregnate AC to improve the RE of gaseous com-ounds [31,42,43]. The results of the tests for these impregnatedetals are shown in Fig. 3. With the same loading rate (1.0 wt.%),
he RE by K (74%) is generally higher than those by Cu (66%), Mn60%), and AC alone (3T-BFU, 67%). Daisey and Hodgson reportedhat the catalyst enhances the removal of NO2 compared to AC alone33]. NOx removal by impregnated AC was reported to be mostly
y catalytic chemisorption rather than by physical absorption [31].n the other hand, in the presence of O2, NO2 is thermodynami-ally favored to be physically adsorbed onto AC surfaces at roomFig. 3. Removal efficiencies with respect to the metals impregnated on AC.
aterials 289 (2015) 184–189 187
temperature [42,44]. Thus, the adsorption capacity will depend onthe AC surface area [45].
We found that the REs of NOx depended on the loading rateand the type of metals. In the case of Cu, the RE during 30 mindecreased from 66 to 42% as the loading rate of Cu increased from1.0 to 6.0 wt.%, showing that the REs of NOx using the AC loadingCu were lower than that of a uncoated AC. On the other hand, forMn, the RE increased as the Mn loading rate increased.
3.3. Impact of K precursors
Fig. 4 shows the effects of different K precursors and their load-ing rates. KI, KOH, KNO3, and KMnO4 were used with loading ratesadjusted from 1 to 5% by dipping 5.0 g AC (JEC) into aqueous solu-tions, followed by drying in an oven. The RE of NO2 was the highestwhen KOH was used as a K precursor, followed by KI, KNO3, andKMnO4. In addition, the RE of NO2 by the AC impregnated with Kwas approximately 38–55% higher than that by AC alone. However,we could not find remarkable differences with respect to the load-ing rates. For KOH, the REs of NO2 decreased from 55 to 52% whenthe loading rates increased from 1 to 5 wt.%. This suggests that theeffect on RE with respect to loading rate is negligible. We founda similar result as in a previous study by Shaughnessy et al. [32].They reported that the air cleaner systems loaded with additionalcarbon sorbent (loaded with KMnO4) were the most effective inNO2 removal of various air purifier systems. In addition, Lee et al.estimated that K+ played a role as a catalyst on the surface of ACimpregnated KOH, as follows [46]:
2KOH + 3NO2 → 2KNO3 + NO + H2O
The BET method was used to estimate the specific surfaceareas of ACs impregnated by the K precursors. The averages(± standard deviation) of the measurements were 1376 ± 23,1311 ± 12, 1317 ± 12, 1268 ± 10 and 1247 ± 9 m2/g for AC alone, 1%KI impregnated AC, 3% KI impregnated AC, 1% KOH impregnated AC,and 3% KOH impregnated AC, respectively. This suggests that thespecific surface areas slightly decreased as K was loaded on the AC,but the difference in the specific surface areas was negligible.
It is important for a practical use of air cleaners to consider theprices of the metal precursors. KI is more expensive than KOH. Thus,KOH is preferable to KI, both due to the lower cost and the higherRE.
3.4. Removal efficiencies of HONO and NOx for a pilot-scale
Fig. 4. Removal efficiencies of NO2 with respect to the loading rates and precursorsof K.
188 J.Y. Yoo et al. / Journal of Hazardous Materials 289 (2015) 184–189
Fp
wt1otpAcawhsttawdm
eHiaPuap3Trti
3
waH((w2tlT(6
ig. 5. Removal efficiencies of HONO and NOx with respect to impregnated com-ounds and contents (1: AC alone, 2: PABA + H3PO4, 3: 3% KOH).
ere 10 ± 2 ppm and 1 ± 0.2 ppm, respectively. The concentra-ion of HONO formed in the chamber was stable, approximately0% variation as NOx, as for a previous study [36]. To achieveptimum air quality in a real indoor environment, the controlechnology needs to remove both NOx and various odorous com-ounds such as acetaldehyde, ammonia, and acetic acid. AlthoughCs impregnated with different metals could remove odorousompounds from indoor air, we also tested with 2.5% PABA (p-minobenzoic acid) plus 6% H3PO4 impregnated on AC. This reagentas selected based on a preliminary study of the REs of acetalde-
yde, ammonia, and acetic acid using 26 different reagents. Thistudy suggested that the PABA + H3PO4 showed the highest effec-iveness of different impregnated compounds and mixtures ofhese reagents (ethylenediamine, octadecylamine, sulfanilinc acid,nilline, n-methylaniline, PABA, H3PO4 and those combinations),ith different loading rates (1–6%) and loading methods. The
etails on this test are available in Table S1 of the Supporting infor-ation.
Based on the preliminary tests, for the pilot chamber study wexamined three types of ACs (uncoated AC (3T-BFU), 2.5% PABA + 6%3PO4, and 3% KOH). The REs of NOx and HONO are presented
n Fig. 5. The REs of HONO and NOx by uncoated AC were 57.4nd 57.3% for 30 min, respectively. REs for HONO and NOx byABA + H3PO4 were 11.7 and 11.5% higher efficiencies than forncoated AC. For 3% KOH, the REs were above 95% for both gases. Inddition, to confirm the stability of removal efficiencies, we com-ared the standard deviation (SD) of the REs. As a result, the SDs by% KOH were 0.49 and 0.12 for REs of HONO and NOx, respectively.hese are slightly lower than those by uncoated AC (1.58 and 1.06,espectively) and by 2.5% PABA + 6% H3PO4 (1.71 and 1.21, respec-ively). This suggests that 3% KOH would be an optimal compoundmpregnated on AC to remove HONO and NOx in indoor air.
.5. Removal efficiencies of odorous compounds
For odorous compounds, which may be present in indoor air,e conducted additional tests to determine REs for acetaldehyde,
mmonia, and acetic acid under the same conditions as those ofONO and NOx. As a result, we found that the RE of acetaldehyde
10 ± 1 ppm) by 3% KOH (40%) was lower than those by AC alone3T-BFU, 61.1%) and 2.5% PABA + 6% H3PO4 (81.8%). A similar resultas found for ammonia. REs of ammonia (10 ± 1 ppm) by AC alone,
.5% PABA + 6% H3PO4, and 3% KOH were 99, 99, and 80%, respec-ively. This indicates that REs of other compounds were relatively
ower when 3% KOH was used to improve the REs of NOx and HONO.o overcome this problem, the mixing ratios of two adsorbents2.5% PABA + 6% H3PO4 and 3% KOH) were adjusted to 8:2, 5:5, and:4, respectively. The effect of mixed adsorbents is shown in Fig. 6.Fig. 6. Effect of mixing ratios on the removal efficiencies of HONO and NOx (2: 2.5%PABA + 6% H3PO4, 3: 3% KOH).
As shown, the REs of NOx and HONO for the ratio of 6:4 were thehighest (95 and 96%, respectively) of the tested ratios. Using a t-testthe REs for the ratio of 5:5 are significantly higher than for the ratioof 8:2 (for NOx, p < 0.0001 and for HONO, p < 0.001). When the ratiosof 5:5 and 6:4 are compared, however, the REs of NOx (p = 0.323)and HONO (p = 0.183) were not significantly different.
We confirmed that NO2 and HONO in indoor air could be suf-ficiently and efficiently removed by an improved activated carbonfilter impregnated with two types of compounds (2.5% PABA + 6%H3PO4 and 3% KOH). However, note that the long-term use ofan activated carbon filter without appropriate maintenance inan indoor environment can result in the desorption of adsorbedgaseous contaminants. Relatively high humidity can also result inthe reduction of removal efficiency in the adsorption process. Thetest conditions are significantly different than conditions typicallyfound in indoor spaces in the following ways: (1) much higher NO2and HONO concentrations during the experiment than encoun-tered indoors; (2) an airtight chamber versus indoor space with airexchange; (3) a much smaller chamber than indoor environmen-tal spaces; and (4) only short-term performance tests comparedto the longer term operation under the actual use of air cleanersin indoor spaces. Accordingly, to determine the effectiveness ofthe improved activated carbon filter in actual indoor environment,additional experiments, including long-term tests of the filter life-time as well as the RE in actual indoor concentrations of NO2 andHONO will be necessary.
4. Conclusions
This study was conducted to develop an activated carbon filterto remove NO2 and HONO in indoor air. Various design parameterssuch as the loading rates of metals and non-metals, precursors ofthe metals, and mixture ratios were investigated. The removal effi-ciency of NOx by generally commercial ACs was as a high as 75%,depending on diverse factors, including the specific surface area ofACs, the particle size, pore structure, carbonization temperature,
and others. With the same loading rate (1.0 wt.%), the RE by K (74%)was generally higher than those by Cu (66%), Mn (60%), and ACalone (67%). However, we did not find remarkable differences fordifferent loading rates for the same K precursor. Based on these
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J.Y. Yoo et al. / Journal of Hazar
esults, we carried out a pilot experiment to determine the opti-um AC to remove odorous compounds (such as acetaldehyde,
mmonia, and acetic acid) as well as NO2 and HONO, and foundhat gaseous air pollutants in indoor air can be sufficiently andfficiently removed by an improved activated carbon filter impreg-ated with two types of compounds (2.5% PABA + 6% H3PO4 and 3%OH). However, more studies, as mentioned above, should be con-ucted to determine whether the results of this study will apply forctual indoor conditions.
cknowledgments
This study was supported by the Technological Innovation R&Drogram(S2076569) funded by the Small and Medium Businessdministration (SMBA, Korea). This research was also supportedy the Nuclear R&D program through the National Research Foun-ation of Korea (NRF) funded by the Ministry of Science, ICT anduture Planning.
ppendix A. Supplementary data
Supplementary data associated with this article can be found,n the online version, at http://dx.doi.org/10.1016/j.jhazmat.015.02.038.
eferences
[1] H. Guo, S.C. Lee, L.Y. Chan, W.M. Li, Risk assessment of exposure to volatileorganic compounds in different indoor environments, Environ. Res. 94 (2004)57–66.
[2] U. Schlink, M. Rehwagen, M. Damm, M. Richter, M. Borte, O. Herbarth,Seasonal cycle of indoor-VOCs: comparison of apartments and cities, Atmos.Environ. 38 (2004) 1181–1190.
[3] U.S. EPA, Exposure factors handbook, 1997,http://www.epa.gov/reg3hwmd/risk/human/rb-concentration table/documents/EFH Final 1997 EPA600P95002Fa.pdf
[4] J. Song, H. Lee, S.D. Kim, D.S. Kim, How about the IAQ in subway environmentand its management? Asian J. Atmos. Environ. 2 (2008) 60–67.
[5] W. Yang, K. Lee, C. Yoon, S. Yu, K. Park, W. Choi, Determinants of residentialindoor and transportation activity times in Korea, J. Expo. Sci. Environ.Epidemiol. 21 (2011) 310–316.
[6] J.R. Sohn, J.C. Kim, M.Y. Kim, Y.S. Son, Y. Sunwoo, Particulate behavior insubway airspace, Asian J. Atmos. Environ. 2 (2008) 54–59.
[7] J.D. Spengler, K. Sexton, Indoor air pollution: a public health perspective,Science 221 (1983) 9–17.
[8] S.S. Park, S.Y. Cho, Performance evaluation of an in situ nitrous acidmeasurement system and continuous measurement of nitrous acid in anindoor environment, J. Air Waste Manage. Assoc. 60 (2010) 1434–1442.
[9] A. Febo, C. Perrino, Prediction and experimental evidence for high airconcentration of nitrous acid in indoor environments, Atmos. Environ. 25A(1991) 1055–1061.
10] K. Lee, X. Jianping, A.S. Geyh, H. Ozkaynak, B.P. Leaderer, C.J. Weschler, J.D.Spengler, Nitrous acid nitrogen dioxide, and ozone concentrations inresidential environments, Environ. Health Perspect. 110 (2002) 145–149.
11] S.S. Park, J.H. Hong, J.H. Lee, Y.J. Kim, S.Y. Cho, S.J. Kim, Investigation of nitrousacid concentration in an indoor environment using an in-situ monitoringsystem, Atmos. Environ. 42 (2008) 6586–6596.
12] M. Brauer, P.B. Ryan, H.H. Suh, P. Koutrakis, J.D. Spengler, Measurements ofnitrous acid inside two research houses, Environ. Sci. Technol. 24 (1990)1521–1527.
13] M. Brauer, P. Koutrakis, G.J. Keeler, J.D. Spengler, Indoor and outdoorconcentrations of inorganic acidic aerosols and gases, J. Air Waste Manage.Assoc. 41 (1991) 171–181.
14] M.I. Khoder, Nitrous acid concentrations in homes and offices in residentialareas in Greater Cairo, J. Environ. Monit. 4 (2002) 573–578.
15] B.P. Leaderer, L. Naeher, K. Balenger, T.R. Holford, C. Toth, J. Sullivan, J.M.Wolfson, P. Koutrakis, Indoor, outdoor, and regional summer and winterconcentrations of PM10, PM2.5, SO4
2− , H+, NH4− , NO3
− , NH3, and nitrous acidin homes with and without kerosene space heaters, Environ. Health Perspect.107 (1999) 223–231.
16] P.K. Simon, P.K. Dasgupta, Continuous automated measurement of the soluble
fraction of atmospheric particulate matter, Anal. Chem. 67 (1995) 71–78.17] J.D. Spengler, M. Brauer, J.M. Samet, W.E. Lambert, Nitrous acid inAlbuquerque, New Mexico, homes, Environ. Sci. Technol. 27 (1993) 841–845.
18] L.J. Folinsbee, Human health effects of air pollution, Environ. Health Perspect.100 (1992) 45–56.
[
aterials 289 (2015) 184–189 189
19] R.J.W. Melia, C. Florey, D.G. Altman, A.V. Swan, Association between gascooking and respiratory disease in children, Br. Med. J. 2 (1977) 149–152.
20] L.M. Neas, D.W. Dockery, J.D. Spengler, F.E. Speizer, B.G. Ferris, Association ofindoor nitrogen dioxide with respiratory symptoms and pulmonary functionin children, Am. J. Epidemiol. 134 (1991) 204–219.
21] X. Meng, C. Wang, D. Cao, C.-M. Wong, H. Kan, Short-term effect of ambientair pollution on COPD mortality in four Chinese cities, Atmos. Environ. 77(2013) 149–154.
22] R. Ehrlich, M.C. Henry, Chronic toxicity of nitrogen dioxide: I. Effect onresistance to bacterial pneumonia, Arch. Environ. Health 17 (1968) 860–865.
23] R. Ehrlich, J.C. Findlay, J.D. Fenters, D.E. Gardner, Health effects of short terminhalation of nitrogen dioxide and ozone mixtures, Environ. Res. 14 (1977)223–231.
24] D.E. Gardner, D.L. Coffin, M.A. Pinigin, G.I. Sidorenko, Role of time as a factor inthe toxicity of chemical compounds in intermittent and continuous exposure.Part 1. Effects of continuous exposure, J. Toxicol. Environ. Health 3 (1977)811–820.
25] H. Li, L. Chen, Z. Guo, N. Sang, G. Li, In vivo screening to determineneurological hazards of nitrogen dioxide (NO2) using Wistar rats, J. Hazard.Mater. 225–226 (2012) 46–53.
26] J.N. Pitts Jr., D. Grosjean, K.A. Cauwenberghe, J.P. Schmid, D.R. Fritz,Photooxidation of aliphatic amines under simulated atmospheric conditions:formation of nitrosamines, nitramines, amides and photochemical oxidant,Environ. Sci. Technol. 12 (1978) 946–954.
27] W.S. Beckett, M.B. Russi, A.D. Haber, R.M. Rivkin, J.R. Sullivan, Z. Tameroglu, V.Mohsenin, B.P. Leaderer, Effect of nitrous acid exposure on lung function inasthmatics: a chamber study, Environ. Health Perspect. 103 (1995) 372–375.
28] T.R. Rasmussen, M. Brauer, S. Kjaergaard, Effects of nitrous acid exposure onhuman mucous membranes, Am. J. Respir. Crit. Care Med. 151 (1995)1504–1511.
29] L.M. Paulin, G.B. Diette, M. Scott, M.C. McCormack, E.C. Matsui, J.Curtin-Brosnan, D.L. Williams, A. Kidd-Taylor, M. Shea, P.N. Breysse, N.N.Hansel, Home interventions are effective at decreasing indoor nitrogendioxide concentrations, Indoor Air 24 (2013) 416–424.
30] F. Haghighat, C.-S. Lee, B. Pant, G. Bolourani, N. Lakdawala, A. Bastani,Evaluation of various activated carbons for air cleaning-towards design ofimmune and sustainable buildings, Atmos. Environ. 42 (2008) 8176–8184.
31] Y.W. Lee, H.J. Kim, J.W. Park, B.U. Choi, D.K. Choi, J.W. Park, Adsorption andreaction behavior for the simultaneous adsorption of NO–NO2 and SO2 onactivated carbon impregnated with KOH, Carbon 41 (2003) 1881–1888.
32] R.J. Shaughnessy, E. Levetin, J. Blocker, K.L. Sublette, Effectiveness of portableindoor air cleaners: sensory testing results, Indoor Air 4 (1984) 179–188.
33] J.M. Daisey, A.T. Hodgson, Initial efficiencies of air cleaners for the removal ofnitrogen dioxide and volatile organic compounds, Atmos. Environ. 23 (1989)1885–1892.
34] Y. Zhang, J. Mo, Y. Li, J. Sundell, P. Wargocki, J. Zhang, J.C. Little, R. Corsi, Q.Deng, M.H.K. Leung, L. Fang, W. Chen, J. Li, Y. Sun, Can commonly-usedfan-driven air cleaning technologies improve indoor air quality? A literaturereview, Atmos. Environ. 45 (2011) 4329–4343.
35] J. Yang, T.T. Zhuang, F. Wei, Y. Zhou, Y. Cao, Z.Y. Wu, J.H. Zhu, C. Liu,Adsorption of nitrogen oxides by the moisture-saturated zeolites in gasstream, J. Hazard. Mater. 162 (2009) 866–873.
36] M. Brauer, T.R. Rasmussen, S.K. Kjaergaard, J.D. Spengler, Nitrous acidformation in an experimental exposure chamber, Indoor Air 3 (1993) 94–105.
37] S. Yamashita, K. Kume, T. Horiike, N. Honma, M. Fusaya, T. Ohura, T. Amagai, Asimple method for screening emission sources of carbonyl compounds inindoor air, J. Hazard. Mater. 178 (2010) 370–376.
38] R.B. Lamorena, W. Lee, Influence of ozone concentration and temperature onultra-fine particle and gaseous volatile organic compound formationsgenerated during the ozone-initiated reactions with emitted terpenes from acar air freshener, J. Hazard. Mater. 158 (2008) 471–477.
39] Y.S. Son, Y.H. Kang, S.G. Chung, H.J. Park, J.C. Kim, Efficiency evaluation ofadsorbents for the removal of VOC and NO2 in an underground subwaystation, Asian J. Atmos. Environ. 5 (2011) 113–120.
40] S. Kasaoka, K. Sakata, E. Tanaka, R. Naitoh, Design of molecular sieve carbon,studies on the adsorption of various dyes in the liquid phase, Inter. Chem.Eng. 24 (1984) 734–742.
41] M.L. Kingsley, J.H. Davidson, Adsorption of toluene onto activated carbonsexposed to 100 ppb ozone, Carbon 44 (2006) 560–564.
42] M.J. Illán-Gómez, E. Raymunho-Pinero, A. García-García, A. Linares-Solano, C.Salinas-Martínenez de Lecea, Catalytic NOx reduction by carbon supportingmetals, Appl. Catal. B 20 (1999) 267–275.
43] C. Márquez-Alvarez, I. Rodriguez-Ramos, A. Guerrero-Ruiz, Removal of NOover carbon supported copper catalysis: II. Evaluation of catalytic propertiesunder different reaction conditions, Carbon 34 (1996) 1509–1514.
44] N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press,Oxford, 1993.
45] M.J. Illán-Gómez, C. Salinas-Martínez de Lecea, A. Linares-Solano, L.R. Radovic,
presence of oxygen, Energy Fuel 12 (1998) 1256–1264.46] Y.W. Lee, D.K. Choi, J.W. Park, Performance of fixed-bed KOH impregnated
activated carbon adsorber for NO and NO2 removal in the presence of oxygen,Carbon 40 (2002) 1409–1417.
