The relationship between optical attenuation and black carbon concentration for ambient and source particles

The Science of the Total Environment, 36 ( 1 9 8 4 ) 1 9 7 - - 2 0 2 Elsevier Science Publishers B.V., A m s t e r d a m - - Printed in T h e Netherlands

197

I'IIE RIiI,AT IONSIt I P BI!'['WEf!NOPTICAL ATTt!NUAT[ON AND BI~..\(~K CARB(4N CONCI!NTIb\TIOX FOR ~}IBII!NT AN[) SOIIR(]E PARTI(~LES*

1..,\. (;UNDI!L, R.I~. I)OI), It. ROSEN and T. NOVAKOV .\pplied

Science Division,

f(~rnia,

Berkeley,

Lawrence B e r k e l e y L a b o r a t o r y ,

California

94720,

University

of Call-

lISA

AISS'I'I~A(]'I' l, i g h t a b s o r p t i o n p r o v i d e s t h e b a s i s f o r a f a s t and n o n d e s t r u c t i v e method f o r d e t e r m i n i n g c o n c e n t r a t i o n s o f b l a c k c a r b o n {BC]. The l a s e r t r a n s m i s s i o n t e c h nique measures the attenuation (ATN) o f v i s i b l e l i g h t a s i t p a s s e s t h r o u g h f i l ter samples, h'e have m e a s u r e d [BC] and ATN s i m u l t a n e o u s l y f o r a l a r g e number of solvent-extracted s o u r c e and a m b i e n t p a r t i c l e samples, using temperatureprogrammed evo l r e d gas a n a l y s i s w i t h c e n t i n u o u s 1i g h t a t t e n u a t i o n m e a s u r e m e n t . 14~r a l l d a t a w i t h ATN -< 2O0, ATN i s d i r e c t l y p r o p o r t i o n a l t o [BC], w i t h t h e proportionality c o n s t a n t = 25.4 ± 1.7 cm ~ ug 1. Because the r e l a t i o n s h i p b e t w e e n ATN and IBC] d o e s n o t depend on t h e o r i g i n o f t h e c a r b o n a c e o u s p a r t i c l e s , m e a s u r e m e n t o f A'FN a l o n e can p r o v i d e a good e s t i m a t e <~f t h e b l a c k c a r b o n concentrat

ion.

l NTROI)IlCTION Particulate b l a c k when i t graphitic

material

or black carbon

due to t h e s e p a r t i c l e s spheric

from ambient a i r

is c o l l e c t e d

radiation

on f i l t e r s , (BC)(ref.1).

before

c a r b o n from b l a c k determination

time consuming. fast

techniqtJe

for

late

of black carbon

c a r b o n by p y r o l y s i s ,

light

and p e r t u r b

of visible

(ref.5]

oxidation,

absorption

the tropo-

r e l y on s e p a r a t i o n or solvent

These methods are de s truc tive

p a p e r we d e s c r i b e

[BC], t h e l a s e r

measures the attenuation

the

(refs.3,4).

o f BC a s CO2.

In this

(ref.2)

appears

of light-absorbing

In t h e a t m o s p h e r e ,

can degrade v i s i b i l i t y

balance

blest m e t h o d s f o r d e t e r m i n a t i o n organic

and c o m b u s t i o n s o u r c e s u s u a l l y

due t o t h e p r e s e n c e

and c a l i b r a t e

transmission light

method

(ATN] a s i t

and o f t e n

a nondestructive (LT~).

of

extracti~m

and

Thi~ t e c h n i q u e

passes through a particu-

s a m p l e on a f i l t e r . In t h i s

study,

we h a v e m e a s u r e d

,4roup o f s o u r c e and a m b i e n t f i l t e r ibrate

the laser

tenuation,

a.

transmission

~ is

the

value

[BC] and ATN s i m u l t a n e o u s l y samples.

The r e s u l t s

method and p r o v i d e of

ATN p e r

unit

a value

for a large

have b e e n u s e d t o c a l f~r the

mass of black

specific

carbon.

It

atis

* T h i s work was s u p p o r t e d by t h e D i r e c t o r , O f f i c e o f E n e r g y R e s e a r c h , O f f i c e o f l l e a l t b and E n v i r o n m e n t a l R e s e a r c h , P h y s i c a l and T e c h n o l o g i c a l R e s e a r c h D i v i s i o n o f t h e II.S. D e p a r t m e n t o f E n e r g y u n d e r c o n t r a c t DE-ACO.~-76SF(~O098 and by t h e N a t i o n a l S c i e n c e F o u n d a t i o n u n d e r c o n t r a c t AT}I 8 2 - 1 0 3 1 3 .

198 important exact

to note

optical

that

the calibration

properties

of black

method is

independent

of knowledge of the

carbon.

SAMPLING Samples of aerosol been prefired

a t 800°C f o r

volume samplers a particle sites)

particles

one of the Berkeley in Austria Typical

ambient

2 9 0 , 0 0 0 BTU h r - 1 )

samples, exhaust

Warren, ~lichigan

sources

segregated,

in Berkeley

(ref.5);

sites

Vienna,

were s o u r c e

travelled

of buildings

exhaust

was s a m p l e d .

was s a m p l e d i n i t s

intercomparison pipe,

representing vents

had

with (two

Austria;

influenced:

freeway;

the sites

in congested

areas.

gas boiler

(input

s a m p l i n g t i m e was 24 h o u r s .

of combustion

an e x t e n s i v e

that

(40 SCDI) a n d low (10-20 SCD0

Some o f t h e s a m p l i n g

were on t h e r o o f s

filters

s a m p l e s were s i z e

was 100 m from a h e a v i l y

and Y u g o s l a v i a

A variety

from i t s

sites

of the

A m b i e n t s a m p l e s were c o l l e c t e d

California;

Yugoslavia.

on q u a r t z - f i b e r

Both h i g h

One-third

o f < 2 um.

and Los A n g e l e s ,

and L j u b l j a n a ,

12 h o u r s .

were u s e d .

cutoff

were collected

study

while

the bus idled

an a v e r a g e

of the uphill

chimney. (ref.6).

A natural

P r o p a n e s o o t was c o l l e c t e d A small diesel

in a vacant

motor vehicle

during

b u s was s a m p l e d 2 m

parking

population,

bore of a highway tunnel

of

garage.

Other

were c o l l e c t e d

and i n a p a r k i n g

in the

garage.

ATTENUATION MEASUREMENTS The laser transmission method measures the attenuation of visible light as it passes through the filter.

ATN is defined as

ATN = -i00 in I/I 0 ,

(I)

where I0 and I are the transmitted loaded filter respectively.

shown that the light attenuation has a linear dependence on

light intensities

Rosen et al.

for the blank and the

(ref.1) and Yasa et al.

(ref.7) have

is due to the presence of black carbon.

If ATN

[BC], then

[BC] = ATN/o , where ~ is

the specific

Attenuation determining LTM. data

(23 attenuation

was m e a s u r e d d u r i n g

[BC] ( s e e n e x t

section)

for black

the evolved gas analysis and a l s o

The two m e a s u r e m e n t s o f ATN a g r e e d (refs.8,9)

carbon.

f o r ATN m e a s u r e d d u r i n g

separately

to within

3%.

EGA a r e g i v e n

(EGA) p r o c e d u r e

a t room t e m p e r a t u r e

for by

Measurement variability in Table

1.

DETERMINATION OF BLACK CARBON Temperature-progran~ed

evolved gas analysis in oxygen

(refs.10,11) with con-

tinuous light transmission measurement was used to identify and quantitate the black carbon.

[ B C ] was determined from the area of the thermogram peak that

199

"['ABl,t!

1

Estimates of measurement variability I imits.

(standard

d e v i a t i o n s ) a :rod q u a n t i t a t i o n

[BC] .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

AjN

lJ,~

-4+2 5 7 6 20

0.3~0.2 0.3 0.6 0.6 2.0

Blanks, extracted, Xb t s b R e p l i c a t i o n o f EGA and ATN o n l y , s t Replication of extraction, E(;A and ATN, s x Limits of d e t e c t i o n 3 % , above blank l.Jmits o f q u a n t i t a t i o n 10Sb, above blank an = t o t a l corresponds

number o f d e t e r m i n a t i o n s ; to the increase

c a r b o n peak i s u s u a l l y

transmission

temperature

peak i s always well r e s o l v e d

black carbon concentration

(Fig.

100,

10 8

la).

1.

k

10 16 ~2

10 0 13

samples.

during combustion.

b e t w e e n 425 and 500°C.

s o u r c e and a m b i e n t s a m p l e s a r e shown i n F i g .

n

-

k = number of" d i f f e r e n t

in light

centered

cm -2

Thermograms o f t y p i c a l

]:or s o u r c e s a m p l e s ,

and can r e a d i l y

Some a m b i e n t

The b l a c k

the high

be u s e d t o d e t e r m i n e

s a m p l e s have d i s t i n c t ,

' 100

2

c O

i Garage

~.

6

c

o~-

2 I-'Io ¢ "~ 10

'

6

4

1

100o

7~

o,~

4F

~//t/¢l//j

0#

r

100~

3.

100

300

500

700

100

~

x

/ A/

300

~

/

^I 500

I 10'

700

Temperature T (°C) F i g . 1. Thermograms o f s o u r c e and a m b i e n t p a r t i c l e s (solid line, untreated samples; dashed line, extracted filters). The s h a d e d a r e a i s b l a c k c a r b o n . Light transmission, in p e r c e n t , i s given in the upper p a r t o f each s e c t i o n .

200 unambiguous black peaks, as illustrated by particulate matter collected near a major highway in Berkeley, California

[Fig. Ib).

Differentiation of black car-

bon from organic carbon in thermograms of some other ambient particulate samples is more difficult, as illustrated in Figs. Ic and d.

Removal of soluble organic

material by solvent extraction leads to thermograms in which isolation of the black peak is straightforward.

This procedure removes most of the organic

carbon; but it leaves black carbon nearly unchanged, as s h o ~

by an average de-

crease in ATN for extracted samples of only 7%, for more than 100 samples.

In

this study all [BC] determinations were performed on samples that had been sequantially extracted by benzene and methanol-chloroform mixture

(l:2,v:v) in

soxhlet devices, in two 6-hr steps (ref. 12). Estimates of measurement variability and quantitation limits are given in Table 1.

The limits of detection and quantitation for blank corrected samples

are 0.6 and 2.0 pg BC cm -2, respectively.

This method of determination of BC

was validated by an extensive ll-]aboratory round-robin comparison

(ref.5).

Our

results were indistinguishable from the mean values obtained in that study for three filter samples of ambient particulate matter from Warren, Hichigan.

RELATIONSHIP BETWEEN ATN AND [BC] ATN and [BC] data are presented in Fig. 2 for all source and ambient samples with ATN ~ 200 and BC 5 8 ug cm -2. I

I

I

I

I

f

For source particles, Fig. 2a, linear --

I

[

(a)

I

[

I

I

(b)

~

160

C

o

I

I

J

, ~

A

o q 160

0 0

120

120

_

[] C

,,~

"7.

80

80

•

Propa~/eSoot Natural Gas Sou¢

O

D,~e Veh c es

T

40

f /

/

-r~""

~

2

l

J

4

~

Parkng Garage

•

Hgh*a~, Tun~

I

l

6

/

40 '

/

8

Warr~, M

~

LjuD~janaYugosava

~

I

I

[]

I

2

I

I

4

V ~nna AL,Slna

I__.L

6

8

Black Carbon (#g cm-2) Fig. 2. The relationship between attenuation and black carbon coneentratlon for ATN ~ 200 and [BC] ~ 8 pg cm -2. Particles from a) sources and b) urban air.

20:

regression

.~ivcs ATN

coefficientl ( 24.1

( 1 ( / . 6 ~ 1 6 . 6 i + (2.1.1 * 2 . S l l R C ] ,

= ().8~.

' 2.3)1BC1,

experimental

For a m b i e n t p a r t i c l e s ,

with r

error,

b e t w e e n ATN and

0.89.

source

[BC].

It

Fi~.

is clear

with

data

r

ATN

from t h e s e

and a m b i e n t p a r t i c l e s

I f we c o m b i n e a l l

2b,

(the correlation

(-0.8 results

follow

the

* 9.8) that,

+

within

same r e l a t i o n s h i p

w i t h ATN ~ 20,~ and

[BC] 5 8 ~g

c m- 2, ATN = (-1.(~

8.7) + (25.4

:*

w i t h r = (/.88. o f equ.

{3]

from e q u . 200.

is

the

during

3).

part

title

the

[1-,)Io,

in

rl'l/e t r a n s m i t t e d

Therefore

of the light

light

incident

fraction

of the

(3)

filter

intensity

loaded light,

of the

is

by a " l i g h t filters

~? o f 7%, when ATN

incident

for

effect pipe"

light

Beer's

that

] f we

that

microscopy.

iuteract

by p a r t i , . l e s

1.

is observed

effect

by o p t i c a l

c~I0, d o e s n o t

interaction

then,

for

a saturation

for absorption

without

slope

[BC] c a n be p r e d i c t e d

and SATN from T a b l e

of sample loading,

available

the

from 0 . 3 ; g cm -2 a t ATN = 50 t o

s~ from e q u .

of heavily

from z e r o ,

of variation

T h i s c o u l d be e x p l a i n e d

where ~ is the fibers

~.

[BC] r a n g e s

using

observation

~,'e a s s u m e t h a t deposit,

indistinguishable

attenuation,

regardless

a t h i g h ATN ( F i g .

the quartz

is

error

ATN = 200,

data,

(3/

c = 25 and a c o e f f i c i e n t

The e x p e c t e d

noticed

intercept

specific

(2) w i t h

all

,

Since this

().(~ ~g cm -2 a t include

* 1.7][BC]

with

the par-

is conducted

with the particle

along

deposit.

Law a b s o r p t i o n , (1)

'

'

1

I

I

I I'~

400

O0

300 0

c o

~= 200 100

, 0

It =

is reduced to

[ :: [O(C~ + { l - ~ ) e x p ( - ~ [ B C ] ) )

0

was

I 10

J

I 20

,

I 30

I

40

B l a c k c a r b o n (~g c m - = ) l ' i g . 5. The r e l a t i o n s h i p b e t w e e n ATN and b l a c k c a r b o n c o n c e n t r a t i o n for data. The s o l i d l i n e g i v e s o = 2 3 . 9 ~ 2 . 0 and ~ : 0 . 0 1 7 2 i n e q u . ( 5 ) .

all

202 Substitution of this expression for ATN in equ. (I) leads to equ. (5): ATN = - 1 0 0 i n For a l l

data

(~ + ( 1 - a ) e x p ( - e [ B C ] ) ) this

model g i v e s

(5)

u = 0 . 0 1 7 2 and o = 2 3 . 9 ± 2 . 0 and r = 0 . 7 6 .

coefficient of variation of the specific attenuation is 8%.

The

All data points

were treated equally, as shown in Fig. 3, since the identity of the black particles does not influence the relationship between ATN and BC.

SUMMARY AND DISCUSSION We have found that source and ambient carbonaceous particles from eight locations in the United States and Europe follow the same relationship between ATN and [BC].

Good predictions of [BC] can be made by using the simple ATN measure-

ment as an alternative to solvent extraction and combustion EGA or other chemical methods, using equ. (2) and ~ = 25.

The ATN measurement is fast, nonde-

structive, cost effective, and will predict

[BC] to within 10% for moderately

loaded filter samples (ATN = l O0); the useful range og the ATN measurement is -2 25-300 ATN units or 1-15 ~g cm BC, using equ. (5) for ATN > 200.

ACKNOWLEDGMENT This work was supported by the Director, Office of Energy Research, Office of Health and Environmental Research, Physical and Technological Research Division of the U.S. Department of Energy under contract DE-AC03-76SF00098 and by the National Science Foundation under contract AT}{ 82-10343.

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3 4 5

6 7 8 9 lO 11 12

H. R o s e n , A.D.A. H a n s e n , L. Gundel and T. Novakov, A p p l . O p t . , 17 (1978) 3859-3861. R.E. W e i s s , A . P . W a g g o n e r , R . J . C h a r l s o n , D.L. T h o r s e 1 1 , J . S . H a l l and L.A. R i l e y , P r o c e e d i n g s , C o n f e r e n c e on C a r b o n a c e o u s P a r t i c l e s in the Atmosphere, L a w r e n c e B e r k e l e y L a b o r a t o r y r e p o r t LBL-9037, 1979, p p . 2 5 7 - 2 6 2 . W.M. P o r c h and M.C. M a c C r a c k e n , A t m o s . E n v i r o n . , 16 (1982) 1 3 6 5 - 1 3 7 1 . R.D. C e s s , A t m o s . E n v i r o n . , a c c e p t e d f o r p u b l i c a t i o n , 1983. P.J. groblicki, S.H. C a d l e , C.C. Ang a n d P.A. M u l l a w a , I n t e r l a b o r a t o r y Comp a r i s o n o f M e t h o d s f o r t h e D e t e r m i n a t i o n o f O r g a n i c and E l e m e n t a l C a r b o n i n Atmospheric Particulate Matter, report GMR 4054, Warren, Michigan, General Motors Research Laboratory, 1983, 25 pp. H.E. Gerber and E.E. Hindman (Eds.), Light Absorption by Aerosol Particles, Hampton, Virginia, Spectrum, 1982, 420 pp. Z. Yasa, N.M. Amer, H. Rosen, A.D.A. Hansen and T. Novakov, Appl. Opt., 18 (1979) 2528-2530. ACS Committee on Environmental Improvement, Anal. Chem., 52 (1980) 2242-2249. H.H. Ku (Ed.), Precision Measurement and Calibration, NBS Special Pub. 300, v. i, Washington, National Bureau of Standards, 1969, pp. 316-317. R.L. Dod, H. Rosen and T. Novakov, Atmospheric Aerosol Research Annual Report, 1977-78, Lawrence Berkeley Laboratory report LBL-8696, 1979, pp. 2-10. H. ~ l i s s a , H. Puxbaum and E. Pell, Z. Anal. Chem., 282 (1976), 109-113. B.R. Appel, E.M. Hoffer, E.L. Kothny, S.M. Wall, H. Haik and R.L. Knights, Environ. Sci. Technol., 13 (1979) 98-104.