Optical and chemical properties of roadside aerosols

The Science

Elsevier

AND

CHEMICAL

CLARKE

and

Department

of

B.V..

131-110 - Printed in The

Amsterdam

PROPERTIES

I.

131

59 (1987)

Enuironment,

Publishers

OPTICAL

A.G.

of the Total

Science

OF ROADSIDE

Netherlands

AEROSOLS

PAPAPANAYOTOU

Fuel

and

Energy,

Leeds

University,

Leeds,

LS2.9JT.

SUMMARY Roadside aerosols have been monitored by a variety of techniques. Optical reflectance of Whatman No.1 filters gave the British Standard smoke value. The optical absorption coefficient was measured by the integrating plate method after collection on Nuclepore filters. As expected there is a good correlation between optical absorption and smoke concentrations but a somewhat poorer correlation of these values with the mass concentration determined gravimetrically. Tc distinguish between local traffic emissions and the general urban background simultaneous monitoring was undertaken at a rooftop site away from the read. The specific absorption coefficient values were higher at the roadside than on the rooftop reflecting the higher proportion of carbonaceous material near to traffic. To assess the importance of the elemental and organic carbon content of the aerosol to the optical properties, two further measurements were made. The fraction of volatile matter in the aerosol was determined bv thermal desorotion and the carbon content of the non-volatile remainder was determined us-ing an elemental analyser. The fraction of volatile matter, which includes hydrocarbons and some inorganic species such as NH4N03. was found to be in the range 24-73X and to be slightly higher away from the road. The non-volatile carbon was found to be in the range 6-25:; by the road. The specific absorption increases with the fraction of non-volatile carbon.

INTRODUCTION It

is

well

known

relationship

to

particulate (based

total

mass

where

there

on

With

are

In

the

.3)

since ularly

the

similar

mass

coal

and

is to

lead

1 km from

004%9697/87/$03.50

much

77::

as

a factor

of

coal

are

darker

site

the

of

(ref.

i).

Ball

of

and

Hume,

Elsevier

the

of

carried

Publishers

London had

was

this

origin particA

the

correlation

of

at

the

Polytechnic There,

the

Hume

emissions,

out

B.V.

and

vehicles.

laboratory.

areas

particulate Ball

in

mass

in

between

engined

involving

authors'

Science

of

value. value

smoke the

Only

emissions

urban

the

2). equality

the

general diesel

cities,

(ref.

shade

airborne

underestimate

the

smoke

smoke

than

was of

the

a variable of

may

2-3 does

has

U.K.

l),

smoke

proportion

proportion

of

0 1987

of

lower

concentrations, the

of

ref.

determining

A much

a high that

atmosphere

valid

in

average

emissions there

concentration

smoke,traffic-generated role

on

measurement

mass

approximately

traffic.

traffic

analysis

than

in

smoke

calibration,

concentrations

that

where

as

Standard determined urban

1963

a significant

by

general

by

high

decline

found

British

the

remain

play

(ref.

less

original

concentration

contributed

total

the

measurements

matter

the

gravimetrically

matter.

value

two

that

the

smoke, in

the

Leeds

132 proportion

of

The elemental with

value

in

relation (see

absorption

Edwards

et

elemental

of

this

(Clarke

and

a major

have

work

side

the and

the

give

an

ed

the

be

obtained more

the

data

aerosol

is

been

obtained

has

particles

in

between was

value

the

the

atmos-

B.S.

smoke,

used

to

investigated

could

by

be

of of

the

local

variations

of

the

other

sources

but

very

fine

predict

in

the

aerosol. reported

aerosols

were

a minor

particles

of

optical

relative

the

made.

the

road-

matter these

of of

In

the

volatile

properties

on

Llm).

of by

Together

proportion

shown

0.1

made both

Some

effect

(s

been

been

main

the

concentrations

been

have the

been

only

have

measurements have

variations

of

roadside

mass

content

in

of have

measurements

Supplementary

from

although

coefficient

and

carbon

University

lo),

components

generated

paper,

the

Leeds

coefficients

presence

present

at 9 and

soluble

absorption the

the

levels

Freshly

the

level.

and

and

to

carbon,

(refs.

water

coefficient

rooftop

arising

of

and

smoke

of

also

of

correlation

the

scattering

11). on

suggesting

indication

emissions

on and

ref.

in

aerosol

aerosols

was

absorption at

previous

effect

reported

smoke,

studies

Morris,

scattering,

the

pollution

by

absorption

to

that

particulate

work

optical

5)

4).

An alternative,

amount

elemental

found

may

2). behaviour

The

ref. absorption

correlations

optical

7).

and

who

Ilhelan,

optical

(ref.

(ref.

6 and

(V.P.H. the

carbon.

characterised

on

good

emissions

refs.

8)

by

a considerable

coefficient (ref.

582

carbon) the

and

engine

atmospheric

emphasis

in

b,

in

al.

sub-Pm The

organic

describing

to

was

although

and

articles

optical

light

determined

coefficient

phere

data

smoke

primarily

parameter,

absorption

well

generated

carbon

(elemental

fundamental

the

is

(graphitic)

total

both

traffic

smoke

data

the

traffic

generat-

particles.

EXPERIMENTAL Measurements side

site

windm5 of

were

was m above

the

main

ground

routes

diesel-engined

5-102.

level

ca.

below.

representing The calibration

Most

samples

and

were

normal

given

in

is

to

50 m from air of

10

week

day

the

to

traffic

is

a high

some

main

roadfloor

lights

on

frequency

fraction parameters

one of

but

a re-

of

diesel

were

made

at

road.

velocities

are

duration

(8.30

hours

The

a first

cars,

overall

of

flow

through

petrol-engined The

vehicles.

1985.

in

There

addition

and

drawn

adjacent

centre.

measurements

media

concentration curve

in

October-December being

site

city

goods

30 m high

day-time, smoke

The

Simultaneous

sampling

period

samples

Leeds

of

is

shown

of

buses

vehicles

various

level.

out

the

curb,

passenger small

The

during

the

proportion

latively

rooftop

made

5 m from

indicated

in

a.m.-6.30

Table

1

p.m.),

conditions.

was

obtained

from

the

British

Standard

the

filter (ref.

reflectance 1).

Samples

using for

the the

133 absorbance

measurements

particle

mass

4503

on

concentrations

microbalance.

the

lowest

ed.

However,

concentration

A back-up

using the

two

filters

methods El,

trations

was

are

TABLE

weights of

when the

less

mass

times

in

Standard

smoke

particles

Mm was rate.

The

0.97,

were

made

agreement

N=65,

at

collect-

therefore

between

regression

line

mass

concen-

The

and

Lin,

absorbance Baker

duction

Charlson

light

particles age.

measurements

and

of

inated

by

tector.

on

Morris,

ref.

by

trap be an 80

the

used

This

the

Rate

involves

the

the

disk

at

24 80

by

than

filter

been

method of

caused

the

and

the

re-

cover-

light

given

of

the

monolayer

scattered

the

have

plate

measurement

less

forward

between

apparatus

2

filter

filter of

e/min.

1.5

integrating

a Nuclepore

intensity

opal

is of since

carbon

of not

content

elemental

the

filter

is

elim-

light

elsewhere

only

coarser

deposits

of

particulate on

the

combustion

since

particles,

the

preventing particles

on

were of

de(Clarke

tube

filter

the

573).

inside

(2

Use

surface

ug

been in

un-

re-

attempted

the

Impaction

This

a

filters

has

melts

using

technique

fibre

collected.

Model

made

this

matter glass

combustion. are

(Bendix particles

aerosols Application

collection in

straightforward

the

roadside

amounts

Although

precipitator and

of analyser.

large

form.

insertion

electrostatic g/min.

an

rather

compact

this some

using

of

the

author's

C.N.H.

requires

12)

Flow

11).

240C

in

followed (ref.

the

of

fortunately comnlended)

surface of

of

of

Measurements Elmer

12).

made

through

the

presence

Details

Pet-kin

(ref.

dependence the

were

transmission

collected Angular

Media

Whatman No.1, cellulose, 25 m clamps Nuclepore, 25 mm, 0.2 pm pore size Whatman, 37 nun, membrane filter, 1 pm pore size Whatman, 55 mm, glass fibre GF/F

Volatiles

ca.

of

off

methods.

Optical absorbance mass concentration Mass concentration

of

a Sartorius drops

Nuclepore-derived

Filter

British

not

with

the

error.

Measurement

may

obtain

1

E.iperimental

and

taken

ug

coefficient the

to

measurements

50

flow

that

used

were these

than

higher

confidence

seriously

also

concentration

(correlation

giving

not

Filter accuracy

ten

good

+ 4.84)

were

the

of at

filters

M,.

levels

measurement

membrane

M,,,=0.97

Nuclepore

process methods

was

therefore

has

a flow

of

removabl'a

and canmade

rate

of

134 aluminium the

cylinders

of

cylinders, in

the

weights

However,

sample

in

of

14).

remove

all

carbon

values

only

iculate

one

be

determined.

that

for

hears

of

this

reason

the

results

is

has

are

upper

(e.g.

does

not The

limits

reported

and

shown

as organic. as

a

elemental

techniques

regarded

total the

There

separating

identify

be

aerosol

than

devolatilisation

techniques

therefore

out

the

heating

analysis.

of

various

by

off

dried of

rather

removed

before

methods

and

N content

carbon

was

temperature

other

should

elemental carbon

24

low

electrostatic

material,

and

the

roof

was

used

before

s/min.)

and

The

then

species.

0f cl-,

rdo3-, so4

to

as

presented

simply

flow

flow

the

the

true

.non-

rates

ments

were

used

imply

particles

such

the

fractions

the

mass

NH4C1,

mass

there as

of

to will

volatile

were

be

used

roadside and

data

obtain

hydrocarbons soluble the

fibre

the

smoke

sampling

matter

samples

matter

collected

expected

that

& Nuclepore

efficiency In

dust.

is

filter

the

discussion

have

not

concentrations

itimasses

are

high measure

the

combined of

some

coarse of

been

hours

since the

filter for

24 and

and

glass

absolute

re-

for

of

It

carbonaceous to

before oven

water

particulate

for

175'C

amount

and

a greater

two at

the

monitored.

those

the

with

chromatography.

the

precipitator

assess

ion

of

roadside

the by

a vacuum

part-

the

preheated

a desicator in

of

leached

samples

accurately

as

includes

To

filters by

in

volatiles

NH4N03).

the

re-entrained

concentration

as

fractions

not

compared

that

lost

both

sampled were

175'C

amounts

rate

ranges

dried

at

at

flow

filters

was

heating

precipitator

as

rates

size

small

taken

same

clean

filter

after

remaining, 2- determined

from

The

matter

were The

particle

exposed

(e.g.

material

samples

the

loss The

organic

Results

that

the

producing

filters.

comparable.

weight

obtained.

inorganic

fibre

so be

weighing

filter

glass

should

weighing.

precipitator

additional using

(80

approaches

the

also

scraped

carbon'.

Having

was

can in

was boats

H and

comparisons

carbon

sample C,

various

the

deposit

the

for

the

that

and

platinum

was

175'C

The

gives

organic

in

obtained

carbon

volatile

interest

at

likely

the

normal

volatile

detailed

is

of

elemental

main the

oven

as

It

the

combustion

variability

carbon

ref.

of

a vacuum

deal

organic

the

bulk

diameter.

Analysis after

since the

great

to

a desicator.

ash

carbon,

mm internal

transferred

overnight and

37

results with

volatiles

and

carbon.

RESULTS Table British The dicated

2 summarises Standard roadside by

the

the

average

values

found

in

this

study.

Smoke smoke rooftop

values values

were

more

(averages

than 45

double and

the

18 ug

m

urban background -3 respectively).

inThe

135 TABLE

2

Average

Values

of

the

Parameters

Measured

-Parameter

Units

E S.

Smoke

u5t.m

Mass

Concentration

i-1g.m -3

Roadside

--

Absorption Coefficient

10-4m-1

Specific Coefficient

Abs.

Volatile

Fraction

Non-Vol. Fraction

Ionic

Non-Vol. Fraction

Carbon

Ash

mg2 -1

will

It

is

not

sum

to

100':.

relationship The

to

with

regression

be

lines

33

37.4

34

2.3

0.7

34

3.9

2.1

34

50

43

36

/J

17

22

27

that

the

gravimetrically

17

27

21

27

four

fractions

determined

t

2.41,

Corr.

Coeff.

0.86

Roof:

Smoke

= 0.70

M,

-

3.67,

Corr.

Coeff.

0.93

The

relationship matter

is

in

illustrated

the

table

in

Fig.

are M,

particulate

listed

mass

= 0.67

of

of Data Pairs

18.0

Smoke

1.

Ho.

73.2

Road:

Fig.

Value

,':

expected

the

Roof

45.5

c//L, rl,J

Fraction

N B.

-3

Value

of determined

British

Standard using

Nuclepore

smoke

with filters.

the

mass

concentration

1.

136

Fig.

2.

The

British

relationship

Standard In

both

mined

from

the

used

for collects

top

site

suspended

use

of

0.92)

which

aerosol.

roof

coefficient

between

road to

fact

The

values

the at

and

Coefficient average

greater

mass,

< 2.5

(corr.

con-

rate

method

sampling on

Pm)

been

method

the

same

gave

in

the

is coeffs.

points

roof-

smoke=0.55x

(ref.

10).

Our

significantly 0.86

composition

lie

near

2.3

and

0.7

as

shown

in

coefficient -4 -1 x 10 ni Fig.

2.

by

the

road

was

as of

the

respectively). The

three

The

regression

lines

less compared

the

line

to

roadside

along

ba

= 0.055

(smoke)

- 0.141,

corr.

coeff.

0.99

ba

= 0.047

(smoke)

- 0.160,

corr.

coeff.

0.97

of

ba

clearly

physical

property

aerosol.

The

are

-4 m -1 10

demonstrates namely smoke

value

and

of

that

which

the can

parameters

absorption be

used

of to

that

correlation

with

on

the

smoke

are

-3 pg m .

smoke both

times

obtained

Roof: units

are

flow

work wintertime

deter-

methods

Nuclepore

correlation

level

all

two a high

for

variability

of

concentration

b

absorption

(values excellent

This

and

limits.

smoke/mass roof

the

Previous

particle

that

mass

had The

sampler

than

quarter

for

matter.

two

the

case

particles.

these

the

one

the

z/3

Road:

The

b,

concentration.

Absorption The

smoke=0.83x(fine

the

about

a dichotomous

lie

relates In

smoke=mass

absorption

are

been

fine

1 shows

by

have

and

Fig.

defined

optical

particulate

relatively

results

However,

would

the

< 15 pm)

well

values filter.

than

made

(mass,

smoke

Nuclepore

total

present

is

the

closer

only

the

smoke.

cases

siderably

between

the

predict

are elemental the

determined carbon absorption

by

the

content coefficient

same of

the and

137

Fig.

3.

The

oarticle in

relationship

mass

this

used

way to

concentration data

the

importance

smoke

The

values

of

rooftop

in

the

to

refine

more

as

that

The

on

O-100

ug m

limited

, the

of

Nucleoore

of

which

there

above

suggest

ha/smoke

a rather lower figure -3 smoke . So further ug m

of

the

= 0.038

M,, - 0.10,

corr.

coeff.

0.89

Roof:

b,

= 0.021

Mn - 0.05,

corr.

coeff.

0.89

values

a (ba/Mn)

clearly

demonstrates

general

urban

both

ba and

aerosol. 15)

are

the

is

close

to

of the

emissions.

of by

the

m

road

-3

deal,

of

can

be

visibility the

range

Previous 2 -1 3 m g work

of work from

is

at data

necessary

The

and

2.1

about of

is

ratio

of

4.5

2 -1 m g 5-5.5

the

mass

is

not

as

good

are

.

aerosol

the

range

lines

Mn pg

roadside

Taking a value

engine

regression

units 2 -1 m g

3.9

that

Mn gives

diesel

and

atmosphere.

This for

10e4mm1

The

with

ba

b

3).

coefficient

Road:

of

(Fig.

absorption

smoke

tion

a great

that for 2 -1 5 m g .

:

the

relationship.

correlation

units

is

on atmospheric

with

with

ba and

filter.

absorption

ratio

O-30

coefficient

the

optical

gave

range

absorption

from

equations -3

(unpublished)

this

optical

smoke, of

regression

site

the

obtained

historical

assess

degradation.

oJr

between

average 2 -1 m g

darker

the for 2 -1 m g

than

(road-roof) the found

specific on

the that

absorpThis

roof. of

the

differences

traffic by

for

generated Japar

et

al.

(ref.

138 Aerosol

Composition

The

percentage

ranged

from

hydrocarbons salts.

extremely + NO,

17::

of

t

mass

dust, four add

lap

of

up

and

to

large

partly

total

because

because

on

the

0,

the

of

average

ash

and

to

average

be

formed

suggesting

in

roadside

of

Table

ash

2 are

non-volatile

ionic

during

that

re-entrained

fraction

listed

H removed

found

non-volatile

on

(7-48-A)

amount

aerosol

N and

The

roof.

variable

The

were

and

the

volatile

especially

heating

chromatography 22':

filters

includes

measured.

very

size.

the

fibre

species, after

a significant

particle to

100%

partly

was

glass figure

inorganic

ion

and

combustion

the

This

routinely

by road

collecting

contributions

of

not

the

on 50-L.

concentrations

analysed by

after was

probably

The

were

of

amounts ion

therefore

mass ash

collected

average

small

were

ions

of

an

with

original

precipitator

matter

with

ammonium

and

so;-

the

The

volatile 73:;

The

small

cl-

to

to

together

ammonium

the

of

24::

was not

21'j.

expected

fractions

combustion

are

over-

not

allowed

for. The

'non-volatile

Allowing

for

carbon'

ca.

15%

be

regarded

volatile/non-volatile carbon

is

is

that

the

consistent

that

organics

particles 2-3.

in

fraction

of

Fig.

Los

the

with

scattered

the

Abs.

coeff. =

suggests that 2 -1 and about 1 m g 2 -1 This latter m 9 .

the

elemental

not

of

more

of

than

elemental

18-27:: specific

the

Non-Vol.

the

non-carbonaceous

the

carbonaceous

+

the

total

carbon.

(ref.

16)

found

sub

2.1

14.9';

of

the

ratio

was

in

which

the

'black

the

This

.m

range carbon'

17).

absorption

coefficient

The line

points

of

are

the

rather

is

1.26

particles

in-

al.

(ref.

(Units:

aerosol

this

et

carbon.

C)

non-volatile carbon,

of

in

regression

17.'. the

'/3

carbon

the

averaged

matter,

Gray

surveys

for

an

the

carbon

non-volatile and

with

Since

example

various

ranged

5-252,

2:l. to

total/elemental

of

(Z

50% volatile

about

and

variation

0.7)

0.147

This

26.7b

carbon

percentage

the

limit is

results

the

from

within

studies,for

The

the

is

upper

carbon

for

total

(corr.

an

other

Angeles.

gives

4 presents

aerosol

Spec.

many

accounted

Novakov

ratio

as

elemental

with

ranged

species

carbon

to

dicates

fraction

inorganic

has

m

2

g

a specific

a specific

-1

)

absorption

absorption

of

of 15-16

figure is subject to considerable uncertainty. Although 2 -1 for elemental carbon have been quoted the majority figures as high as 15 m g 2 -1 basis the absorption coof authors favour a figure nearer 10 m g . On that -4 -1 efficient is given simply by ba (10 m ) = 0.1 x (Elemental Carbon pg m -3). Finally, Clayton Total for total

the

the

relationship

(ref.

2)

found

Carbon

=

0.42

range carbon

O-200 indicates

of

(smoke) + -3 smoke. pg m that

the

smoke

to

4.34 Taking elemental

carbon

(Units: elemental carbon

may

be

ug m

considered. -3

carbon concentration

Bailey

and

) to

be one is

Ca.

third 14% of

of

139

‘. 0

1-ig.

4.

The

age

of

the

smoke

B).

Their

on

of

This

carbon.

However

ponded

to

12 pg

was

s,moke.

14 71

? 4% of ug of

the

This

using

50 on

carbon.

figure,

as

(m2

of

the is

pg

the

findings

pg

value

smoke.

particulates

the

50

was

Standard

non-volatile

elemental

with that

this

coefficient

g-l)

with

percent

aerosol.

consistent

British

20

C %

absorption the

indicated

corresponding thus

in

is

correlation

is

specific

carbon

value.

elemental the

variation

non-volatile

Non -;‘d

of

smoke

Nuclepore

is

et

smoke.

at

our

carbon

is

(al.

(ref.

toGi

calibration

ug

filter

slightly

Edwards

corresponded

O.E.C.U. 42.5

Non-volatile

anticipated,

of

smoke

1-19 of

curve

The

and

elemental

carb-

roadside

site

of

about

17% or

about

24%

which

therefore

higher

than

the

a major

role

in

corres-

figures

of

for

carbon.

CONCLUSIONS Traffic-generated pollution.

carbonaceous They

>lmetric

mass

properties

result

carbon -indirect

marked

concentrations, (filter

However, properties

content methods

the of

also and

there

because of

local

but

reflectance

concentrations. optical

in

aerosols

aerosol monitoring

of

variations in

the

optical

is

common these

carbon

not

dependence

the

in

atmosphere.

urban

elemental provide

grav-

optical

and between

the

and

the

coefficient)

on

air

smoke

between

relationship

inter-relationships in

only

relationship absorption

a consistent

their and

play

the the

mass two

or valuable

black

140

REFERENCES 1. 2.

3.

a.

9. 10.

11.

12.

13.

14.

15.

16.

17.

British Standard 1747, Part 2, 1969, HMSO, London. D.L.R. Bailey and P. Clayton, The measurement of suspended particle and total carbon concentrations in the atmosphere using standard smoke shade methods, Atmos. Environment, 16 (1982), 2683-2690 D.J. Ball and R. Hume, The relative importance of vehicular and domestic emissions of dark smoke in Greater London in the mid-197Os, the significance of smoke shade measurements, and an explanation of the relationship of smoke shade to gravimetric measurements of particulate, Atmos. Environment, 11, (1977) 1065-1073. V.P.tI. llhelan, Smoke and Sulphur Dioxide pollution in Leeds, M.Phil. Thesis, University of Leeds, 1980. D.C. Siegla and G.W. Smith (Eds.), Particulate Carbon: Formation during combustion, Plenum Press, New York, 1981. G.T. Wolff and R.L. Klimisch (Eds.), Particulate Carbon: Atmospheric life cycle, Plenum Press, New York, 1982. H. Malissa, H. Puxbaum and T. Novakov (Eds.), Proc. of the 2nd Internat. Conf. on Carbonaceous Particles in the Atmosphere (1983). The Science of the Total Environment, Vol. 36, 1984. J.D. Edwards, J.A. Ogren, R.E. Ueiss and R.J. Charlson, Particulate air A comparison of British pollutants: 'smoke' with optical absorption coefficient and elemental carbon concentration, Atmos. Environment, 17 (1983) 2337-2341. A.G. Clarke, M.J. Willison and E.M. Zeki, A comparison of urban and rural aerosol composition using dichotomous samplers, Atmos. Environment, 18, (1984) 1767-1775. M.J. Willison, A.G. Clarke and E.M. Zeki, Seasonal variation in atmospheric aerosol concentration and composition at urban and rural sites in northern England, Atmos. Environment, 19 (1985) 1081-1089. A.G. Clarke and K.J. Morris, The relative contributions of scattering and absorption of light to visibility degradation by aerosols, in 6. Versino and H. Ott (Eds.), Physico-Chemical Behaviour of Atmospheric Pollutants, Proc. of the 2nd European Symposium, D. Reidel Pub. Co., Dordrecht, Holland, 1982, pp.280-286. C.I. Lin, M.B. Baker and R.J. Charlson, Absorption coefficient for atmosH method for measurement, Applied Optics, 12(1973) 1356pheric aerosol: 1363. R.K. Patterson, Automated Pregl-Dumas technique for determining total carbon, hydrogen and nitrogen in atmospheric aerosols, Anal. Chem, 45 (1973) 605-609. S.H. Cadle and P.J. Groblicki, An evaluation of methods for the determination of organic and elemental carbon in particulate samples in particulate carbon: Atmospheric Life Cycle, ref. 6 above, pp.89-108. S.M. Japar, A.C. Szkarlat and W.R. Pierson, The determination of the optical properties of airborne particulate emissions from diesel engines in Science of the Total Environment, ref. 7 above, pp.121-130. H.A. Gray, G.R. Cass, J.J. Huntzicker, E.K. Heyerdahl and J.A. Rau, Elemental and organic carbon particle concentrations: A long term prospective, in Science of the Total Environment, ref. 7 above, pp.l7-26. T. Novakm, Soot in the atmosphere, in Particulate Carbon: Atmosphere Life Cycle, ref. 6 above, pp.19-37.