Passive Sampling of Nitrogen Dioxide and Sulfur Passive Sampling of Nitrogen Dioxide and Sulfur Dioxide in Ambient Air of Chiang MaiDioxide in Ambient Air of Chiang Mai

Shakya, K.M.Shakya, K.M.11, P. Thavornyutikarn, P. Thavornyutikarn11, S. Chantara, S. Chantara11, , W. SaipunkaewW. Saipunkaew11, H. Mosbaek, H. Mosbaek22

7 December 2004

1. Environmental Science Program, Faculty of Science, Chiang Mai University, Thailand2. Technical University of Denmark, Denmark

Passive SamplingPassive Sampling

• First described by Palmes First described by Palmes et al.et al. (1976) in occupational hygiene (1976) in occupational hygiene

for measuring NOfor measuring NO22 in indoor air in indoor air

• Based on diffusion principleBased on diffusion principle

• Collection of gas on sampling medium soaked with absorbent Collection of gas on sampling medium soaked with absorbent

by chemical absorption (Krupa and Legge, 2000)by chemical absorption (Krupa and Legge, 2000)

• Sampling medium – filter papers or steel meshesSampling medium – filter papers or steel meshes

• Absorbent – depends on gas of interestAbsorbent – depends on gas of interest

1. 1. IntroductionIntroduction

AdvantagesAdvantages

• Light, cheap, robust, easy to Light, cheap, robust, easy to

operateoperate

• Small, soundless and reusableSmall, soundless and reusable

• On-site power and pumping of air On-site power and pumping of air

not requirednot required

• Do not require attention during Do not require attention during

samplingsampling

• Supports “green analytical Supports “green analytical

chemistry“chemistry“

• Favors to have many sampling Favors to have many sampling

sitessites

• Very appropriate for large scale Very appropriate for large scale

monitoringmonitoring

• Long sampling timeLong sampling time

• No standard proceduresNo standard procedures

• Inability to obtain short-term Inability to obtain short-term

peakspeaks

• Possibility of interferences from Possibility of interferences from

meteorologymeteorology

• Doubts on reliability Doubts on reliability

DisadvantagesDisadvantages

Objectives of this researchObjectives of this research

• To determine the accuracy of passive samplers by comparing with To determine the accuracy of passive samplers by comparing with

active samplers, active samplers,

• To compare the results among different kinds of passive samplers, To compare the results among different kinds of passive samplers,

• To compare the results of NOTo compare the results of NO22 concentrations from concentrations from

spectrophotometer and ion chromatograph, andspectrophotometer and ion chromatograph, and

• To determine the levels of NOTo determine the levels of NO22 and SO and SO22 concentrations in ambient concentrations in ambient

air using passive samplers in Chiang Mai cityair using passive samplers in Chiang Mai city

Preparation of diffusion tubesPreparation of diffusion tubes

• diffusion tubes – polystyrene (ps), polyethylene (pe), and “Gradko” tubesdiffusion tubes – polystyrene (ps), polyethylene (pe), and “Gradko” tubes

• Sampling medium - Whatman no. 40 filter paperSampling medium - Whatman no. 40 filter paper

• Absorbents for NOAbsorbents for NO2 2 – TEA and NaOH plus NaI– TEA and NaOH plus NaI

• Absorbents for SOAbsorbents for SO2 2 – TEA, Na– TEA, Na22COCO33, and NaOH, and NaOH

2. 2. ExperimentalExperimental

Installation of diffusion tubes inside the polyethylene box

at 1.5 m above ground level

3-9 sampling sites

Sampling period – October 2003 to February 2004

5.4 cm 5.4 cm1.2 cm 1.3 cm

TEA coated filter paper

Polyethylene cap

Polystyrene tube Polyethylene tube

Diagram of diffusion tube

Analysis of NOAnalysis of NO22-- by spectrophotometer by spectrophotometer

• Extraction with DI waterExtraction with DI water

• Color formation with reagent mixture (Sulfanilamide + N-1 naphthyl Color formation with reagent mixture (Sulfanilamide + N-1 naphthyl ethylene diamine hydrochloride solution)ethylene diamine hydrochloride solution)

• Measured at 540 nm on PerkinElmer Lambda 25 SpectrophotometerMeasured at 540 nm on PerkinElmer Lambda 25 Spectrophotometer

Analysis of NO2- and SO4

2- by Ion Chromatograph

• Extraction with Milli-Q water

• Oxidation with 0.15% H2O2

• eluent: 1.80 mM Na2CO3/ 1.70 mM NaHCO3

• 1.5 ml/min eluent flow rate

• 3 s background conductivity

• 25 l sample loop volume

• BDS, Barspec Data System

3. 3. Results & DiscussionResults & Discussion

PE tubes - 14.22% > PS tubesPE tubes - 14.22% > PS tubes

Correlation between NOCorrelation between NO22 measurements by PS and PE tubes measurements by PS and PE tubes

(Analysis by Spectrophotometer)(Analysis by Spectrophotometer)

y = 0.9602x - 2.5042

r2 = 0.9276

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

pe tubes (g/m3)

ps

tub

es

(g

/m3 )

Correlation between SOCorrelation between SO22 measurements from 4 weeks exposure of PS measurements from 4 weeks exposure of PS

and PE tubesand PE tubes

y = 0.5765x + 5.0788r2 = 0.5941

0

5

10

15

20

25

30

0 5 10 15 20 25 30

pe tubes (g/m3)

ps

tub

es

(g

/m3 )

PE tubes - 1.95% > PS tubesPE tubes - 1.95% > PS tubes

Correlation between SOCorrelation between SO22 measurements from 2 weeks exposure of PS measurements from 2 weeks exposure of PS

and PE tubesand PE tubes

PS tubes - 1. 62% > PE tubesPS tubes - 1. 62% > PE tubes

y = 0.9738x + 0.093

r2 = 0.7969

0

5

10

15

20

25

0 5 10 15 20

pe tubes (g/m3)

ps

tub

es

(g

/m3 )

NONO22 measurements (01/22/2004 – 02/05/2004) measurements (01/22/2004 – 02/05/2004)

0

20

40

60

80

100

120

140

160

180

200

A B C D E F G H I

Sampling site

NO

2 co

nce

ntr

atio

n ( g

/m3 )

Grako tubes

ps tubes

pe tubes

0

5

10

15

20

25

30

35

40

A B C D E F G H R

Sampling site

SO

2 co

nce

ntr

atio

n ( g

/m3 )

Gradko tubes

ps tubes

pe tubes

SOSO22 measurements (01/22/2004 – 02/19/2004) measurements (01/22/2004 – 02/19/2004)

Correlation between NOCorrelation between NO22 measurements from active and passive sampling for measurements from active and passive sampling for

2 weeks period2 weeks period

PS tubesy = 0.7125x - 1.1235

R2 = 0.9066

PE tubesy = 0.8927x - 2.0987

R2 = 0.9217

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35

Active sampling (ppbv)

Dif

fusi

on

tu

bes

(p

pb

v)

PS tubes

PE tubes

Underestimation:54.13% PS tubes and 15.39% PE Underestimation:54.13% PS tubes and 15.39% PE

tubestubes

Detection limits for instrumentDetection limits for instrument

• SpectrophotometerSpectrophotometer

– 0.09 0.09 g/ml NOg/ml NO22--

• Ion ChromatographIon Chromatograph

– DL: 0.04 DL: 0.04 g/ml NOg/ml NO22-- and 0.02 and 0.02 g/ml SOg/ml SO44

2-2-

– Minimum Detectable Quantity: 0.48 Minimum Detectable Quantity: 0.48 g.sec NOg.sec NO22-- and and

0.36 0.36 g.sec SOg.sec SO442-2-

Detection limits for passive sampling method

• NONO22: : 1.6 1.6 g/mg/m33 for PS and 3.9 for PS and 3.9 g/mg/m33 for PE tubes for PE tubes

• SOSO22 (2 weeks) (2 weeks): : 1.9 1.9 g/mg/m33 for PS and 1.7 for PS and 1.7 g/mg/m33 for PE tubes for PE tubes

• SOSO22 (4 weeks) (4 weeks): : 1.4 1.4 g/mg/m33 for PS and 2.1 for PS and 2.1 g/mg/m33 for PE tubes for PE tubes

• Diffusion tubes (ps and pe) showed good trends of NODiffusion tubes (ps and pe) showed good trends of NO22 and SO and SO22

concentrationsconcentrations

• Good correlation between ps and pe tubesGood correlation between ps and pe tubes

• Good correlation between active and passive sampling Good correlation between active and passive sampling

measurements for NOmeasurements for NO22 but variable for SO but variable for SO22

• Underestimation for NOUnderestimation for NO2 2 and overestimation for SOand overestimation for SO22 by diffusion by diffusion

tubes compared to active sampling; also supported by “Gradko” tubes compared to active sampling; also supported by “Gradko”

tubestubes

• Variations in blank measurementsVariations in blank measurements

• Precision - 18.12% for NOPrecision - 18.12% for NO22 and 16.36% for SO and 16.36% for SO22

4. 4. ConclusionConclusion

Errors can be reducedErrors can be reduced for diffusion tubes : for diffusion tubes :

• Use of protective sheltersUse of protective shelters

• Keeping tubes in an airtight containers during Keeping tubes in an airtight containers during

transittransit

• Storage of tubes in a refrigerator and not Storage of tubes in a refrigerator and not

storing for very long timestoring for very long time

• Diffusion tubes with separate cap and body Diffusion tubes with separate cap and body

partsparts

• Use of a porous membrane at mouth of the Use of a porous membrane at mouth of the

tubetube

• Good laboratory practiceGood laboratory practice