A New, Portable, Real-time Ozone Monitor

Douglas R. Black Department of Civil and Environmental Engineering

University of California at Berkeley

California Air Resources Board January 25, 2000

Introduction

u People spend ~90% of time indoors

u Ozone routinely monitored outdoors

u Ozone penetration factor ranges from 0.1 to 0.9

u Need to understand indoor levels to assess and

control ozone exposure

Ozone Exposure Assessment

u Epidemiological studies of adverse health effects

u Ozone control strategies / regulatory standards

u Methods of assessing ozone exposure

< direct measurement

< indirect measurement

< modeling

Need for Portable Ozone Monitor

u Assessment of exposure requires accurate characterization of indoor ozone < UV ozone monitors are large, noisy, and

expensive u Assessment of acute ozone exposures requires high

temporal resolution < diffusive badge samplers provide ozone

concentration averaged over 8 hours or more and require costly and time-consuming lab analysis

Sensor Design

u Piezoelectric quartz crystal

u Polybutadiene coating

u Reaction with ozone causes mass increase and

decrease in oscillation frequency

u Rate of change of frequency is proportional to ozone

concentration

Piezoelectric Quartz Crystal

Quartz

\· I

I I

Gold Electrode

- - - - --

I

- - -

Ozone / Polybutadiene Chemistry

[ C C C C ] + O n 3

O O O

C C C C

r-----------, I I -: © ~ -1 L I I I I I I I I I I

f-­~--

/

1----------------, I I I I ---: © I

--~ I I I I I I I I I I I

►AA ~ 1---1 ------1

-----. r------=========::::!..........

Flow Cell

Crystal

Base

O-Ring

Sensor Housing

Portable Ozone Monitor

u Stand-alone unit

< sampling pump

< programmable datalogger

u Teflon filter to remove particles

u Nafion dryer to remove water vapor

u Flow control by critical orifice

□

D I

POM Component Layout

pump

nafion dryer

data

logg

er

batte

ry

sens

or

orifice

POM Component Layout

Monitor Operation

u Coat crystals to be used for sampling

u Install and condition crystals

u Run sampler (1000 ppb-hr)

u Download ozone concentration data from logger

with laptop PC

u Remove crystals, clean, and re-coat

Laboratory Testing

u Vary sample air flow rate

u Calibration

u Interference testing

< NO2, water vapor, NO, HNO3, and toluene

• •

Sensor Response vs. Air Flow Rate

2.0

1.6

1.2

0.8

0.4

0.0

y=3.2x+0.41 R2=0.98

0.0 0.2 0.4 0.6 0.8 1.0 Flow Rate (LPM)

POM Measurements in Lab over 24 hrs

1330 1730 2130 130 530 930 1330 Time of Day (hhmm)

0 50

100 150 200 250 300 350

[O3] Monitor [O3] UV Photo

+ 0 X

Monitor Calibration Curve 400

300

200

100

0

y = 58.5x R2 = 0.997

0 2 4 6 Sensor Response (Hz/min)

8 kHz 10 kHz 12 kHz 14 kHz

Sensor Response to Ozone and NO2

120

100

80

60

40

20

0

1000

800

600

400

200

0

[NO

2] (

ppb)

0 60 120 180 240 Elapsed Time (min)

[O3] Sensor [O3] Actual [NO2]

Sensor Response to Ozone and Water Vapor

0 20 40 60 80

100 120

2000 2100 2200 2300 Time of Day (hhmm)

[O3] Monitor [O3] Actual RH

Field Sampling

u Offices in Riverside

< two POMs, one UV monitor indoors

< building ventilation fixed

u Residences in Pasadena

< two POMs, one UV monitor indoors

< one POM, one UV monitor outdoors

< vary ventilation with doors and windows

Outdoor POM Measurements at Residence 1

50

25

0 930 1100 1230 1400 1530 1700

Time of Day (hhmm)

POM UV Photo

Outdoor POM Measurements at Residence 2

80

60

40

20

0 930 1100 1230 1400 1530 1700

Time of Day (hhmm)

POM UV Photo

Indoor POM Measurements at Residence 2

0 10 20 30 40 50 60 70

930 1100 1230 1400 1530 1700 Time of Day (hhmm)

POM 1 POM 2 UV Photo

Photocopy Room Measurements 40

30

20

10

0 900

45

30

15

0 1100 1300 1500 Time of Day (hhmm)

Hou

rly

Avg

No.

of

Cop

ies

UV Photo POM1 POM2 No. of Copies

Significance of New Monitor

u Low-cost, small-size, and real-time measurements

< schools, hospitals, nursing homes, in-transit

< assess indoor ozone sources

< exposure model development

u Technology has potential for personal monitoring

Personal Monitoring

u Prototype battery-operated monitor

< personal sampling pump

< Nafion dryer with desiccant

u Lighter, smaller enclosure

u Fits in standard backpack

u Preliminary tests with two subjects in Sacramento

Personal and Outdoor Ozone Measurements

80

60

40

20

0 10 11 12 13 14 15 16 17 18

Time Outdoor POM PSD

Acknowledgments

u Prof. Robert Harley, UC Berkeley

u Susanne Hering and Mark Stolzenburg, ADI

u California Air Resources Board

< Tom Phillips and Peggy Jenkins