cap.16 sampling

8/11/2019 Cap.16 Sampling

1/15

6

A m bi en t A i r

Samp l ing

I E L E M E N T S O F A S A M P L I N G S Y S T E M

T h e p r i n c i p a l r e q u i r e m e n t o f a s a m p l i n g s y s t e m is t o o b t a in a s a m p l e t h a t i s

r e p r e s e n t a t i v e o f t h e a t m o s p h e r e a t a p a r t i c u l a r p l a c e a n d t i m e a n d t h a t c a n b e

e v a l u a t e d a s a m a s s o r v o l u m e c o n c en t ra t io n . 1 T h e s a m p l i n g s y s t e m s h o u l d

no t a l t e r t he c he mic a l o r phys i c a l c ha r a c t e r i s t i c s o f t he s a mp le i n a n unde s i r -

a b le m a n n e r . T h e m a j o r c o m p o n e n t s o f m o s t s a m p l i n g s y s t e m s a r e a n in l et

m a n i f o l d a n a i r m o v e r a c o l le c ti o n m e d i u m a n d a f l o w m e a s u r e m e n t d e v ic e .

T h e i nl e t m a n i f o l d t r a n s p o r t s m a t e r i a l fr o m t h e a m b i e n t a t m o s p h e r e t o t h e

c o l le c ti o n m e d i u m o r a n a l y t ic a l de v i ce p r e f e r a b l y i n a n u n a l t e r e d c o n d i ti o n .

T h e i n l e t o p e n i n g m a y b e d e s i g n e d f o r a s p e ci fi c p u r p o s e . A l l i n l e ts f o r a m b i -

e n t s a m p l i n g m u s t b e r a i n p r o o f. I n l e t m a n i f o l d s a r e m a d e o u t o f g l as s

T e fl on s t a i n le s s s t ee l o r o t h e r i n e r t m a t e r i a l s a n d p e r m i t th e r e m a i n i n g c o m -

p o n e n t s o f t h e s y s t e m t o b e l o c a te d a t a d i s t a n ce f r o m t h e s a m p l e m a n i f o l d

i n l e t . T h e a i r m o v e r p r o v i d e s t h e f o r c e t o c r e a t e a v a c u u m o r l o w e r p r e s s u r e

a t t h e e n d o f t h e s a m p l i n g s y s t e m . I n m o s t i n s ta n c e s a i r m o v e r s a re p u m p s .

1 R eal-time rem ote mo nitoring systems discussed in Chapter 18 do not require subsequent

analysis.

4 5 7


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45 8 16 Am bient Air Sampl ing

T h e c o l l e c t i o n m e d i u m f o r a s a m p l i n g s y s t e m m a y b e a l i q u i d o r s o l i d s o r -

b e n t fo r d i s s o l v i n g g as e s , a fi lt e r su r f ace fo r co l l ec t in g p a r t ic l e s , o r a ch a m b e r

t o c o n t a i n a n a l i q u o t o f a i r f o r a n a l y si s . T h e f lo w d e v i c e m e a s u r e s t h e v o l u m e

o f a i r a s s o c i a t e d w i t h t h e s a m p l i n g s y s t e m . E x a m p l e s o f f l o w d e v i c e s a r e

mas s f l o w me t e r s , r o t ame t e r s , an d c r i t i c a l o r i f i c e s .

S a m p l i n g s y s t e m s c a n t a k e s e v e ra l fo r m s a n d m a y n o t n e c e s s ar i ly h a v e a ll

four co m po ne n ts (Fig . 16 .1 ) . F igu re 16 .1(a) is typ ica l o f m an y ex t rac t ive sam -

p l i n g t ec h n i q u es i n p rac t ice , e .g . SO 2 i n l i q u i d s o rb en t s an d p o l y n u c l ea r a ro -

ma t i c h y d ro ca rb o n s o n s o l id s o rb en ts . F i g u re 1 6.1 (b ) i s u s ed fo r o p en - f ace

f i l t e r co l l ec t ion , in which the f i l t e r i s d i rec t ly exposed to the a tmosphere be ing

s am p l ed . F i g u re 1 6 .1 (c ) i s an ev a cu a t e d co n t a i n e r u s ed t o col lec t an a l i q u o t o f

a i r o r g a s t o b e t r an s p o r t ed t o t h e l ab o ra t o ry fo r ch emi ca l an a l y s is ; e .g ., p o l-

i s h ed s t a in l e s s s tee l c an is t e rs a r e u s e d t o co ll ect am b i en t h y d ro ca rb o n s fo r a ir

t o xi c an a ly s i s. F i g u re 1 6 .1 (d ) i s t h e b as is fo r ma n y o f t h e au t o m a t e d co n t i n u o u s

a n a l y z e r s, w h i c h c o m b i n e t h e s a m p l i n g a n d a n a l y ti c a l p r o c es s e s i n o n e p ie c e o f

eq u i p m en t , e .g . co n t i n u o u s am b i en t a i r m o n i t o r s fo r SO 2, O 3, an d N O x .

R e g a r d l e s s o f t h e c o n f i g u r a t i o n o r t h e s p e c i f i c m a t e r i a l s a m p l e d , s e v e r a l

c h a r a c t e r is t ic s a r e i m p o r t a n t f o r a ll a m b i e n t a i r s a m p l i n g s y s t e m s . T h e s e a r e

co l l ec t i o n ef fi ci ency , s am p l e s t ab il it y , r eco v e ry , m i n i m a l i n t e r f e r en ce , a n d an

u n d e r s t a n d i n g o f t h e m e c h a n i s m o f c o ll ec t io n . I de a ll y , t h e f ir s t t h r e e w o u l d

b e 1 0 0% a n d t h e re w o u l d b e n o i n t er f e re n c e o r c h a n g e i n t h e m a t e r i a l w h e n

co l lec ted .

O n e e x a m p l e i s s a m p l i n g f o r S O 2 . L i q u i d s o r b e n t s f o r SO 2 d e p e n d o n t h e

s o l u b i l i t y o f SO 2 i n th e l i q u i d co l l ec ti o n me d i u m . C e r t a i n l i q u i d s a t th e co r r ec t

p H a r e c a p a b l e o f r e m o v i n g a m b i e n t c o n c e n t r a t io n s o f S O2 w i t h 1 00 % ef fi-

c i en cy u n t i l t h e ch a rac t e r i s t i c s o f t h e s o l u t i o n a r e a l t e r ed s o th a t n o m o re SO 2

m a y b e d i s s o l v e d i n t h e v o l u m e o f l iq u i d p r o v i d e d . U n d e r t h e se c i r cu m -

s t an ces , s a m p l i n g i s 1 00 % e f fi c ien t fo r a l i mi t ed t o t a l mas s o f SO2 t r an s f e r r ed

t o th e s o l u t io n , a n d t h e t e c h n i q u e is a c c e p t a b l e a s l o n g a s s a m p l i n g d o e s n o t

c o n t i n u e b e y o n d t h e t i m e t h a t t h e s a m p l i n g s o l u t io n i s s a t u r a t e d [ 1] . A s e c o n d

e x a m p l e i s th e u s e o f s o l id s o r b e n t s s u c h a s T e n a x fo r v o la t il e h y d r o c a r b o n s

(a)

M a n i fo ld

b) c)

Ma n i fo l d

d)

Ma n i fo l d

C o l le c t io n C o l l e c t io n

E v a c u a t e d F l o w

m e d i u m m e d i u m c o n t a i n e r m e t e r

[

i r i r D e te c t io n

m o v e r m o v e r c h a m b e r

F l o w F l o w i r

m e t e r m e t e r m o v e r

xhaust 1 1

E x h a u s t I I E x h a u s t

Fig. 16.1. Schem aticdiagram of various types of samp ling systems.


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II Sam pling Systems for Gaseous Pollutants 45 9

b y t h e p h y s i c a l a d s o r p t i o n o f t h e i n d i v i d u a l h y d r o c a r b o n m o l e c u l e s o n

ac t ive s i te s o f the so rb en t [2 ]. Co l lec t ion e f fi c iency d rops d ras t i ca l ly w he n

the ac t ive s it e s beco m e sa tu ra ted .

S a m p l e s t a b il it y b e c o m e s i n c r e a s in g l y i m p o r t a n t a s th e t i m e b e t w e e n s a m -

p l ing a nd ana lys i s inc reases . Ef fec ts o f t em pera tu re , t r ace con tam inan t s , and

chem ica l r eac t ions can cause the co l l ec ted spec ies to be lo s t f rom the co l lec -

t i on m e d i u m o r to u n d e r g o a t r a n s f o r m a t i o n t h a t w i ll p r e v e n t i t s r ec o v er y .

Ne ar ly 100 r ecovery is a l so r equ i r ed becau se a va r iab le r ecovery r a te w i l l

p rev en t q uan t i f i ca t ion o f the ana lys is . I n te r f e rence sh ou ld be m in im al and , i f

p r e s e n t , w e l l u n d e r s t o o d .

II S A M P L I N G S Y S T E M S F O R G A S E O U S P O L L U T A N T S

G a s e o u s p o l l u t a n t s a r e g e n e r a l l y c o l l e c t e d b y t h e s a m p l i n g s y s t e m s

sh ow n in F ig . 16 .1 (a) -(d ). The s a m pl in g m an i f o ld ' s on ly func t ion i s to tr ans -

p o r t t h e g a s fr o m t h e m a n i f o l d i n le t to t h e c o ll e ct io n m e d i u m i n a n u n a l t e r e d

s ta te . The man i fo ld mus t be made o f nonreac t ive ma te r i a l . Tes t s o f ma te r i a l

fo r man i fo ld cons t ruc t ion can be made fo r spec i f i c gases to be s ampled . In

mos t cases , g la s s o r Tef lon w i l l no t adso rb o r r eac t w i th the gases . No con-

d e n s a t i o n s h o u l d b e a l l o w e d t o o c c ur i n t h e s a m p l i n g m a n i f o l d .

T h e v o l u m e o f t h e m a n i f o l d a n d t h e s a m p l i n g f l o w r a t e d e t e r m i n e t h e

t ime r equ i r ed fo r the gas to move f rom the in le t to the co l l ec t ion med ium.

Th is r e s idence t ime can be m in im ize d to dec rease the lo s s o f r eac t ive spec ies

i n t h e m a n i f o l d b y k e e p i n g t h e m a n i f o l d a s s h o r t a s p o s si b le .

The co l l ec tion me d i um fo r gases can be l iqu id o r so l id so rben t s , an evacu-

a ted f l a sk , o r a c ryogen ic t r ap . L iqu id co l l ec t ion sys tems t ake the fo rm o f

b u b b l e r s w h i c h a r e d e s i g n e d t o m a x i m i z e t h e g a s - l i q u i d i n t e r f a c e . E a c h

des ign i s an a t t empt to op t imize gas f low ra te and co l l ec t ion e f f i c i ency .

H i g h e r f l o w r a t e s p e r m i t s h o r t e r s a m p l i n g t i m e s . H o w e v e r , e x c e s s i v e f l o w

rates cause the col lec t ion ef f ic iency to dro p belo w 100 .

A E x tr a ct iv e S a m p l i n g

When bubb le r sys tems a re used fo r co l l ec t ion , the gaseous spec ies gener -

a l l y u n d e r g o e s h y d r a t i o n o r r e a c t i o n w i t h w a t e r t o f o r m a n i o n s o r c a t i o n s .

F o r e x a m p l e , w h e n SO 2 a n d N H 3 a r e a b s o r b e d i n b u b b l e r s t h e y f o r m H S O 3

a n d N H O ~ - , a n d t h e a n a l y t i c a l t e c h n i q u e s f o r m e a s u r e m e n t a c t u a l l y d e t e c t

t h e s e i on s. T a b le 1 6 . 1 g i v e s e x a m p l e s o f g a s e s w h i c h m a y b e s a m p l e d w i t h

b u b b l e r s y s t em s .

B u b b l e r s a r e m o r e o f t e n u t i l i z e d f o r s a m p l i n g p r o g r a m s t h a t d o n o t

r e q u i re a la r g e n u m b e r o f s a m p l e s o r f r e q u e n t s a m p l i n g . T h e a d v a n t a g e s o f

these types o f s ampl ing sys tems a re low cos t and po r tab i l i ty . The d i s advan-

tages a re the h igh deg ree o f sk il l and ca re fu l han d l ing nee ded to ensu re qua l i ty

resu l ts . So l id so rbe n t s such as Tenax , XAD, an d ac t iva ted ca rbon ( charcoal )


4/15

T A B L E 1 6 . 1

C ol l e c t i on o f G as e s b y b s or p t i on

S o r p t i o n A i r f l o w M i n i m u m C o l l e ct i o n

G a s S a m p l e r m e d i u m ( L m - 1 ) s a m p l e ( L) e f f ic i e n c y A n a l y s i s I n t e r f e r e n c e s

A m m o n i a M i d g e t i m p i n g e r 2 5 m L 0 .1 N s u l f u ri c 1 - 3 1 0 N e s s l e r r e a g e n t - -

a c i d

P e t r i b u b b l e r 1 0 m L o f a b o v e 1 - 3 1 0 + 9 5 N e s s l e r r e a g e n t - -

B e n z e n e G l a s s b e a d c o l u m n 5 m L n i t r a ti n g a c i d 0 .2 5 3 - 5 + 9 5 B u t a n o n e m e t h o d O t h e r a r o m a t i c

h y d r o c a r b o n s

C a r b o n d i o x i d e F r i t t e d b u b b l e r 1 0 m L 0 .1 N b a r i u m 1 1 0 - 1 5 6 0 - 8 0 T i t r a t i o n w i t h 0 . 05 N O t h e r a c i d s

h y d r o x i d e o x a l i c a c i d

E t h y l b e n z e n e F r i t t e d b u b b l e r 1 5 m L s p e c t r o g r a d e 1 2 0 + 9 0 A l c o h o l e x t r a c t io n , O t h e r a r o m a t i c

o r m i d g e t i m p i n g e r i s o o c t a n e u l t r a v i o l e t a n a l y s i s h y d r o c a r b o n s

F o r m a l d e h y d e F r i tt e d b u b b l e r 1 0 m L 1 s o d i u m 1 - 3 2 5 + 9 5 L i b e r a t e d s u l fi t e M e t h y l k e t o n e s

b i s u l f i t e t i t r a t e d , 0 .0 1 N

H y d r o c h l o r i c F r i t t e d b u b b l e r 0 . 00 5 N s o d i u m 1 0 1 0 0 + 9 5

a c i d h y d r o x i d e

H y d r o g e n M i d g e t i m p i n g e r 1 5 m L 5 c a d m i u m 1 - 2 2 0 + 9 5

s u l f i d e s u l f a t e

i o d i n e

T i t r a t i o n w i t h 0 .0 1 N

s i l v e r n i t r a t e

A d d 0 . 0 5 N i o d i n e ,

6 N s u l f u r i c a c i d ,

b a c k - t i t r a t e 0 . 01 N

s o d i u m t h i o s u l f a t e

L e a d , t e t r a e t h y l , D r e s c h e l - t y p e 1 0 0 m L 0 .1 M i o d i n e 1 . 8 -2 . 9 5 0 - 7 5 1 0 0

a n d s c r u b b e r m o n o c h l o r i d e

t e t r a m e t h y l i n 0 .3 N

M e r c u r y , d i e t h y l , M i d g e t i m p i n g e r 1 5 m L o f a b o v e 1 .9 5 0 - 7 5 9 1 - 9 5

a n d d i m e t h y l

M i d g e t i m p i n g e r 1 0 m L 0 .1 M i o d i n e 1 - 1. 5 1 0 0 9 1 - 1 0 0

m o n o c h l o r i d e i n . 3 N

h y d r o c h l o r i c a c i d

N i c k e l c a r b o n y l M i d g e t i m p i n g e r 1 5 m L 3 2 .8 5 0 - 9 0 + 9 0

h y d r o c h l o r i c a c i d

D i t h i z o n e

S a m e a s a b o v e

D i t h i z o n e

C o m p l e x w i t h

a l p h a - f u r i l - d i o x i m e

O t h e r c h l o r i d e s

M e r c a p t a n s ,

c a r b o n

d i s u l fi d e , a n d

o r g a n i c s u l f u r

c o m p o u n d s

B i s m u t h ,

t h a l li u m , a n d

s t a n n o u s t i n

S a m e a s a b o v e

C o p p e r


5/15

N i t r o g e n F r i t t e d b u b b l e r 2 0 - 3 0 m L S a l t z m a n 0 .4

d i o x i d e ( 6 0 -7 0 ~ m p o r e r e a g e n ta

s i z e )

O z o n e M i d g e t i m p i n g e r 1 p o t a s s iu m 1

i o d i d e i n 1 N

p o t a s s iu m h y d r o x i d e

P h o s p b i n e F r i t t e d b u b b l e r 1 5 m L 0 .5 s i l v e r 0 . 5

d i e t h y l d i t h i o c a r b a m a t e

i n p y r i d i n e

S t y r e n e F r i t t e d m i d g e t 1 5 m L s p e c t r o g r a d e 1

i m p i n g e r i s o o c t a n e

S u l f u r d i o x i d e M i d g e t i m p i n g e r , 1 0 m L s o d i u m 2 - 3

f l i t t e d r u b b e r t e t r a c h lo r o m e r c u r a t e

S a m p l e u n t i l 9 4 - 9 9

c o l o r a p p e a r s ;

p r o b a b l y

1 0 m L o f a i r

2 5 + 9 5

5 86

2 0 + 9 0

2 99

T o l u e n e M i d g e t i m p i n g e r 1 5 m L M a r c a l i s o l u t i o n 1 2 5 9 5

d i i s o c y a n a t e

V i n y l a c e t a t e F r i t t e d m i d g e t T o l u e n e 1 .5 1 5 + 9 9 ( 8 4

i m p i n g e r a n d w i t h

s i m p l e m i d g e t f l i t te d

i m p i n g e r i n s e r ie s b u b b l e r

o n l y )

R e a c t s w i t h

a b s o r b i n g s o l u t i o n

M e a s u r e s c o l o r

o f i o d i n e l i b e r a te d

C o m p l e x e s w i t h

a b s o r b i n g s o l u t i o n

U l t r a v i o l e t a n a l y s i s

R e a c t i o n o f

d i c h l o r o s u l f i t o -

m e r c u r a t e a n d

f o r m a l d e h y -

d e p a r a r o s a n i l i n e

D i a z o t i z a ti o n a n d

c o u p l i n g r e a c ti o n

G a s c h r o m a t o g r a p h y

O z o n e i n

f i v e f o l d e x c e s s

p e r o x y a c y l

n i t r a t e

O t h e r o x i d i z i n g

a g e n t s

A r s i n e , s t i b i n e ,

a n d h y d r o g e n

s u l f i d e

O t h e r a r o m a t i c

h y d r o c a r b o n s

N i t r o g e n

d i o x i d e , b

h y d r o g e n

s u l f i d e c

M a t e r i a l s

c o n t a i n i n g

r e a c t i v e

h y d r o g e n

a t t a c h e d t o

o x y g e n

( p h e n o l ) ; c e r t a i n

o t h e r d i a m i n e s

O t h e r s u b s t a n c es

w i t h s a m e

r e t e n t io n t i m e

o n c o l u m n

a 5 g s u l f a n i l ic ; 1 40 m L g l a c i a l a c e t i c a ci d ; 2 0 m L 0 . 1 a q u e o u s N - ( 1 - n a p h t h y l ) e t h y l e n e d i a m i n e .

b A d d s u l f a m i c a c i d a f t e r s a m p l i n g .

c F i l t e r o r c e n t r i f u g e a n y p r e c i p i t a t e .

Source: P a g n o t t o , L . D . , a n d K e e n a n , R . G . , S a m p l i n g a n d a n a l y s i s o f g a s e s a n d v a p o r s , i n The Industrial Environment--Its Evaluation and Control

p p . 1 6 7- 17 9 . U S D e p a r t m e n t o f H e a l t h , E d u c a t i o n , a n d W e l fa r e, U S G o v e r n m e n t P r i n t i n g O f f i c e , W a s h i n g t o n , D C , 1 9 7 3.


6/15

462

16. mbient ir Sampl ing

are used to samp le hydro carb on ga ses by t r ap ping the spec ies on the ac t ive

s i tes of the su rface of the sorben t . Figu re 16.2 i l lus t rates the load ing of act ive

s i tes wi th increas ing sam ple t ime. I t i s cr it ical that the brea kth rou gh sam pling

volum e the amo un t o f a i r pas s ing th ro ug h the tube tha t s a tura tes it s absorp-

t ive capac i ty no t be exceeded . The break through volume i s dependent on

the concent ra t ion of the gas be ing sam pled and the absorp t ive capac i ty of the

sorbent. Thi s m eans tha t the user m us t ha ve an es t imate of the upp er l imi t o f

concen t ra t ion for the gas be ing samp led .

Once the sam ple has been co llec ted on the so l id sorbent the tube i s s ea led

and t r ansp or ted to the ana ly t ica l labora tory . To recover the sorbed gas two

technique s m ay be used . The tube m ay be hea ted whi le an iner t gas i s f low-

ing th ro ug h i t. A t a suff ic ien tly h igh t em pera ture the absorbed m olecules

are desorb ed and car r i ed ou t o f the tube wi th the iner t gas s tr eam. The gas

s t r eam m ay th en be passed th rou gh a preconcent ra t ion t r ap for in jec tion in to

a gas chro m atog raph for chemica l ana lys is . The second technique is liqu id

ext rac t ion of the sorbent and su bseq uen t l iqu id chroma tography . Som et imes

a der ivat izat ion s tep is necessary to conver t the col lected mater ial chemi-

ca lly in to com pou nd s w hich wi l l pas s th ro ugh the co lum n mo re eas ily e .g .

convers ion of carboxyl ic acids to methyl es ters . Sol id sorbents have

increased ou r ab i l ity to me asure h ydro carb on spec ies unde r a var ie ty of f ie ld

condi t ions . How ever th is t echnique requi res g rea t sk il l and sophis t i ca ted

equ ipm ent to ob ta in accura te resu lt s . Care mu s t be t aken to min imize prob-

lems of contam ina t ion of the co ll ect ion mediu m sam ple ins tab i l ity on the

sorbent and incomp le te recovery of the sorbed gases .

Special technique s are em ploy ed to sam ple for gases and par t iculate m at ter

s i mu l t aneous l y [ 3] . S amp l ing s ys tems have b een deve l oped w h i ch pe r mi t

the r em oval o f gas -phase molecu les f rom a mov ing a i r s tr eam by d i f fus ion to

a coa ted sur face and permi t the passage of par t i cu la te mat te r downs t ream

a) ~ Col lec t ion me dium

Inlet Out let

b )

~ , . e .9

04

CO )

h ta t3

~ ~ - - - . . . . . . 7

Length of sampl ing tube

F i g . 1 6.2 . S o l i d s o r b e n t c o l le c t i o n t u b e . a ) T h e tu b e is p a c k e d w i t h a g r a n u l a r m e d i u m . b )

A s t h e h y d r o c a r b o n - c o n t a i n i n g a i r is p a s s e d t h r o u g h t h e c o l l e c t io n t u b e a t t l , t2 , a n d t 3, t h e c o l -

l e c ti o n m e d i u m b e c o m e s s a t u r a t e d a t i n c r e a si n g l e n g t h s a l o n g t h e t ub e .


7/15

III Sam pling Syste m s for Particulate Pollutants 46 3

for col lec t ion on a f i lte r or o ther med ium . T hese d i ffusion d en ud ers are used

to sample for SO2 or ac id gases in the presence of par t icula te mat ter . This

type o f sampl ing has been deve loped to min imize the in t e r fe rence o f gases

in pa r ti cu la t e sam pl ing and v ice ve rsa .

The th i rd technique, sho w n in Fig . 16 .1 c) , involves col lec t ion of an a l iquot

of a i r in i ts gas eou s s ta te for t rans po rt back to the analy t ica l labora tory . Use

of a preevacuated f lask permi ts the col lec t ion of a gas sample in a specia l ly

pol ish ed s ta in less s teel conta iner . By use of pre ss ure -v olu m e re la t ionships , i t

is poss ib l e to remov e a kn ow n vo lume f rom the t ank fo r subsequen t chemica l

analysis . An othe r m ean s of collec ting gaseou s sam ples i s the col lapsib le bag.

Bags m ade o f po lym er f ilms can be used fo r co l lec tion and t ransp or t o f sam-

p les . The a i r may be pumped in to the bag by an ine r t pump such as one

using f lexib le meta l be l lows, or the a i r may be sucked in to the bag by p lac-

ing the bag in an a i r t ight conta iner which i s then evacuated . This forces the

bag to expan d , d r aw ing in the ambien t a i r sample .

B I n S i tu S a m p l i n g a n d A n a l y s i s

The four th sampl ing t echn ique invo lves a combina t ion o f sampl ing and

analysis . The analy t ica l technique i s incorporated in a cont inuous moni tor-

ing ins t rumen t p l aced a t t he sampl ing loca t ion . Mos t o f t en , t he moni to r ing

equipment i s located inside a shel ter such as a t ra i ler or a smal l bui ld ing ,

wi th the ambien t a i r d rawn to the moni to r th rough a sampl ing man i fo ld .

The m onitor then ex tracts a small fract ion of air from the m anifold for analysis

by an au tom ated t echn ique , wh ich ma y be con t inuous o r d i sc ret e. Ins t rume n t

m a n u fa c t u re r s h a v e d e v e l o p e d a u t o m a t e d

n s tu

moni tors for severa l a i r

pol lu tan ts , in c ludin g SO2, NO , NO2, 03 , and CO.

This approach i s a l so improving for organic pol lu tants . For example , rea l -

t im e g a s c h ro m a t o g ra p h -m a ss sp e c t ro m e t e r sa n d o p e n P a t e r F ou ri er .

III S A M P L I N G S Y S T E M S F O R P A R T IC U L A T E P O L L U T A N T S

Sam pl ing fo r pa rt ic l e s in the a tmosp here invo lves a d i f fe ren t se t o f pa ra m-

eters f rom those used for gases . Par t ic les are inherent ly larger than the mol-

ecu les o f N2 and 02 in the su r ro un d ing a i r and the re fo re behav e d i f fe ren tly

wi th inc reas ing d iamete r . W hen one is sampl ing fo r pa r t i cu la te ma t t e r i n the

atmosphere , three types of informat ion are of in teres t : the mass concent ra-

t ion , s ize , and chemical composi t ion of the par t ic les . Par t ic le s ize i s impor-

t an t in de te rm in ing adverse e ffec ts and a tm ospher i c remo va l p rocesses . The

US En v i ronm enta l P ro tec tion Ag ency h as spec if i ed a PM2.5 sam pl ing

method fo r compl i ance moni to r ing fo r the Na t iona l Ambien t Ai r Qua l i ty

S tandard s NA AQS) fo r pa r t i cu la t e ma t t er . Th is t echn ique m us t be able to

sample pa r t i cu la t e ma t t e r wi th an ae rodynamic d iamete r l e ss than 10~m

with a prescribed efficiency.


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464

1 6. A m b i e n t A i r S a m p l i n g

P a r t ic l e s in th e a t m o s p h e r e c o m e f r o m d i f f e re n t s o u r ce s , e. g. c o m b u s t i o n ,

w i n d b l o w n d u s t , a n d g a s - t o - p a r ti c l e c o n v e r s i o n p r o c e s s e s s e e C h a p t e r 10 ).

F i g u r e 2 . 2 i l lu s t r a te s t h e w i d e r a n g e o f p a r t i c le d i a m e t e r s p o t e n t i a l l y p r e s e n t

i n th e a m b i e n t a t m o s p h e r e . A t y p i c a l s iz e d i s t r i b u t i o n o f a m b i e n t p a r ti c l e s is

s h o w n i n Fi g. 2.3. T h e d i s t r i b u t i o n o f n u m b er , s u r f ace , an d m as s can o ccu r o v e r

d i f fe r e n t d i a m e t e r s f o r t h e s a m e a e ro s o l. V a r i a t io n i n c h e m i c a l c o m p o s i t i o n a s

a fu n c t i o n o f p a r t i c l e d i am e t e r h a s a l s o b ee n o b s e rv ed , a s s h o w n i n T ab l e 8 .5 .

T h e m a j o r p u r p o s e o f a m b i e n t p a r t i c u la t e s a m p l i n g i s t o o b ta i n m a s s c o n -

c e n t r a t i o n a n d c h e m i c a l c o m p o s i t i o n d a t a , p r e f e r a b l y a s a f u n c t i o n o f p a r t i -

c l e d i ame t e r . T h i s i n fo rma t i o n i s v a l u ab l e fo r a v a r i e t y o f p ro b l ems : e f f ec t s

o n h u m a n h e a l th , i d e n ti f ic a t io n o f p a r t ic u l a t e m a t t e r s o u rc e s , u n d e r s t a n d i n g

o f a t m o s p h e r i c h a z e , a n d p a r t i c l e r e m o v a l p r o c e s s e s .

T h e p r i m a r y a p p r o a c h i s to s e p a r a t e t h e p a r ti c le s f r o m a k n o w n v o l u m e o f

a i r a n d s u b j e c t t h e m t o w e i g h t d e t e r m i n a t i o n a n d c h e m i c a l a n a l y s i s . T h e

p r i n c i p a l m e t h o d s f o r e x t r a c ti n g p a r ti c l es f r o m a n a i r s t r e a m a r e fi lt r at io n a n d

i m p a c t i o n . A ll s a m p l i n g t e c h n i q u e s m u s t b e c o n c e r n e d w i t h t h e b e h a v i o r o f

p a r t i c l e s i n a m o v i n g a i r s t r e a m . T h e d i f f e r e n c e b e t w e e n s a m p l i n g f o r g a s e s

a n d s a m p l i n g f o r p a r t i c l e s b e g i n s a t t h e i n l e t o f t h e s a m p l i n g m a n i f o l d a n d

i s d u e t o th e d i s c r e t e m a s s a s s o c i a t e d w i t h i n d i v i d u a l p a r t ic l e s.

A B e h a v i o r o f P a r t i cl e s a t S a m p l i n g I n l e t s

S a m p l i n g e r r o r s m a y o c c u r a t t h e i n l e t , a n d p a r t i c l e s m a y b e l o s t i n t h e

s a m p l i n g m a n i f o l d w h i l e b e i n g t r a n s p o r t e d t o t h e c o l l e c t i o n s u r f a c e . F i g u r e

1 6 . 3 i l l u s t r a t e s t h e f l o w p a t t e r n s a r o u n d a s a m p l i n g i n l e t i n a u n i f o r m f l o w

a)

b )

c )

d)

v

r - - - - -

Fig . 16 .3 . The s t reaml ine f low pa t t e rn s a rou nd a sam p l ing i n l e t i n a un i fo r m f low f ie ld .


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I I I

Sam plin g System s for articulate ollutants

465

f ie ld. F igu re 16 .3 a ) show s tha t w he n no a i r i s pe r m i t t ed to f low in to the

in le t , the s t r eaml ine f low moves a round the edges o f the in le t . As the f low

ra te th rough the in le t inc reases , more and more o f the s t r eaml ines a r e

a t t rac ted to the in le t . F igu re 16 .3 b) i s ca l led the

isokinetic condition

i n w h i c h

the s am pl in g f low ra te i s equa l to the f low f i e ld r a te . An ex am ple i s an in le t

w i t h i t s o p e n i n g i n t o t h e w i n d p u l l i n g a i r a t t h e w i n d s p e e d . W h e n o n e i s

s ampl ing fo r gases , th i s i s no t a s e r ious cons t r a in t because the compos i t ion

of the ga s wi l l be th e sam e u nd er a l l in le t f low ra tes ; i. e. , there i s no f rac t ion-

a t ion o f the a i r s am ple by d i f f e ren t gaseou s m olecu les .

Trans fo rm in f r a red , d i f f e r en t i a l op t i ca l abso rp t ion spec t roscopy , and

t u n e d l a se r s a re b e i n g u s e d w i t h m u c h s u cc e ss .

Pa r t i c l e - con ta in ing a i r s t r eams p resen t a d i f f e r en t s i tua t ion . F igu re 16.3 b ),

the i sok ine t ic case , i s the idea l case . The idea l s am ple in le t wo u l d a lw ays f ace

i n to t h e w i n d a n d s a m p l e a t t h e s a m e r a te a s th e i n s t a n t a n e o u s w i n d v e l o ci ty

an impo ss ib i li ty ) . U nd er i sok ine t i c s am pl in g cond i t ions , pa ra l l e l a ir s tr eam s

f low in to the s am ple in le t, ca r ry ing w i t h the m par t i c l e s o f a l l d iam ete r s capa-

b l e o f b e i n g c a r r i e d b y t h e s t r e a m f lo w . W h e n t h e s a m p l i n g r a t e i s l o w e r t h a n

the f low fie ld F ig . 16 .3 c)) , the s t ream lines s tar t to d ive rge ar ou nd the edge s

o f the in le t and the l a rge r pa r t ic l e s w i th m ore ine r t i a a r e unab le to fo l low the

s t r e a m l i n e s a n d a r e c a p t u r e d b y t h e s a m p l i n g i n l e t . T h e o p p o s i t e h a p p e n s

w h e n t h e s a m p l i n g r a te i s h i g h e r t h a n t h e f lo w f ie ld . T h e i n le t c a p t u r e s m o r e

s t r eaml ines , bu t the l a rge r pa r ti c l e s nea r the edge s o f the in le t m ay be un ab le

to fo l low the s t r eaml ine f low and escape co l l ec t ion by the in le t . The in le t

m ay b e d es ig ne d for par t ic le s ize frac t iona t ion; e .g ., a PM2.5 in le t wi l l exclude

par t i c l e s l a rge r than 2 .5 ~m ae ro dyn am ic d iam ete r s ee F ig . 2 .4 ).

These ine r t i a l e f f ec t s become le s s impor tan t fo r pa r t i c l e s w i th d iamete r s

l es s t h a n 5 ~ m a n d f o r lo w w i n d v e lo c it ie s , b u t f o r s a m p l e r s a t t e m p t i n g t o

co l lec t pa r t i c l e s above 5 ~m, the in le t des ig n a nd f low ra tes becom e im por -

t a n t p a r a m e t e r s . I n a d d i t i o n , t h e w i n d s p e e d h a s a m u c h g r e a t e r i m p a c t o n

s a m p l i n g e r ro r s a s s o c i a t e d w i t h p a r t ic l e s m o r e t h a n 5 ~ m i n d i a m e t e r [4 ].

Af te r the g rea t e f fo r t t aken to ge t a r ep resen ta t ive s ample in to the s am-

p l ing man i fo ld in le t , ca re mus t be t aken to move the pa r t i c l e s to the co l l ec -

t i on m e d i u m i n a n u n a l t e r e d f o r m . P o t e n t ia l p r o b l e m s a r i se f r o m t oo l o n g o r

t o o t w i s t e d m a n i f o l d s y s t e m s . G r a v i t a t i o n a l s e t t l i n g i n t h e m a n i f o l d w i l l

r em ove a f r ac t ion o f the ve ry l a rge pa r ti c l e s. L a rge r pa r t i c l e s a r e a l so sub jec t

to lo s s by impac t ion on wa l l s a t bends in a man i fo ld . Pa r t i c l e s may a l so be

sub jec t to e lec t rosta t ic fo rces wh ich w i l l cause the m to mig ra te to the wa l l s o f

n o n c o n d u c t i n g m a n i f o ld s . O t h e r p r o b l e m s i n c l u d e c o n d e n s a t i o n o r a g g lo m -

era t ion du r ing t r ans i t t ime in the man i fo ld . These cons t r a in t s r equ i r e s am-

p l ing m an i fo lds fo r pa r t i c le s to be a s sho r t and have as few ben ds as pos s ib le .

The co l l ec t ion t echn ique invo lves the r emova l o f pa r t i c l e s f rom the a i r

s t r eam. The two p r inc ipa l me thods a re f i l t r a t ion and impac t ion . F i l t r a t ion

cons is ts of co l lec t ing par t ic les on a f i l te r sur face by three processes : d i rec t

in te r cep t ion , ine r t i a l impac t ion , a nd d i f fus ion [5 ] . F i l t r a tion a t t em pts to

r e m o v e a v e r y h i g h p e r c e n t a g e o f t h e m a s s a n d n u m b e r o f p a r ti c le s b y t h e se


10/15

46 6 16 Am bient Air Sampl ing

t h r ee p ro ces s e s . A n y s i ze c l a s s i f i ca t i o n i s d o n e b y a p rec l a s s i f i e r , s u ch a s an

i m p ac t o r , b e fo re t h e p a r t i c l e s t r ea m re ach e s t h e s u r f ace o f t h e f il te r .

IV P A S S IV E S A M P L I N G S Y S T E M S

Pass ive (o r s t a t i c )

s a m p l i n g s y s t e m s

a r e d e f i n e d a s th o s e t h a t d o n o t h a v e a n

a c t iv e a i r - m o v i n g c o m p o n e n t , s u c h a s th e p u m p , t o p u l l a s a m p l e t o t h e c ol -

l e c t i o n m e d i u m . T h i s t y p e o f s a m p l i n g s y s t e m h a s b e e n u s e d f o r o v e r 1 0 0

y e a r s . E x a m p l e s i n c l u d e t h e le a d p e r o x i d e c a n d l e u s e d t o d e t e c t t h e p r e s e n c e

o f S O 2 i n t h e a t m o s p h e r e a n d t h e d u s t f a l l b u c k e t a n d t r a y s o r s l i d e s c o a t e d

w i t h a v is c o u s m a t e r i a l u s e d t o d e t e c t p a r t i c u l a t e m a t te r . T h is t y p e o f s y s t e m

s u ff e rs f r o m i n a b i li t y t o q u a n t i f y t h e a m o u n t o f p o l l u t a n t p r e s e n t o v e r a s h o r t

p e r i o d o f t i me , i. e. , l e ss t h a n I w ee k . T h e p o t e n t i a l l y d e s i r ab l e ch a ra c t e r i s t ic s

o f a s t a t i c s a m p l i n g s y s t e m h a v e l e d t o f u r t h e r d e v e l o p m e n t s i n t h i s t y p e o f

t e c h n o l o g y t o p r o v i d e q u a n t i t a ti v e i n f o r m a t i o n o n p o l l u t a n t c o n c e n t r a t i o n s

o v e r a fi x e d p e r i o d o f t im e . S t at ic s a m p l i n g s y s t e m s h a v e b e e n d e v e l o p e d f o r

u s e i n th e o c c u p a t i o n a l e n v i r o n m e n t a n d a r e a ls o u s e d t o m e a s u r e t h e e x p o -

s u r e l e v e l s in t h e g e n e r a l c o m m u n i t y , e . g. , r a d o n g a s i n r e s id e n c e s .

T h e ad v an t ag es o f s t a t i c s amp l i n g s y s t ems a r e t h e i r p o r t ab i l i t y , co n v en -

i en ce , r e l i ab i l i t y , an d l o w co s t . T h e s y s t ems a r e l i g h t w e i g h t an d can b e

a t t ach ed d i r ec t l y t o i n d i v i d u a l s . N o n s t a t i c s amp l i n g s y s t ems can , o f co u r s e ,

a l s o b e a t t a c h e d t o i n d i v i d u a l s , b u t a r e l e s s c o n v e n i e n t b e c a u s e t h e p e r s o n

m u s t c a r r y a b a t t e r y - p o w e r e d p u m p a n d i ts b a t te r ie s . S ta ti c s a m p l i n g s y s t e m s

a re v e ry r e li ab le , an d t h e m a t e r i a l s u s e d l i mi t th e co s t s t o accep t ab l e l ev e ls .

T w o p r i n c i p l e s a r e u t il i z e d i n t h e d e s i g n o f s t at ic s a m p l e r s : d i f f u s io n a n d

p e r m e a t i o n [ 6, 7] . S a m p l e r s b a s e d o n t h e d i f fu s io n p r i n c i p le d e p e n d o n t h e

m o l e c u l a r i n t e r a c t io n s o f N 2, 0 2 , a n d t r a c e p o l l u t a n t g a s e s. I f a c o n c e n t r a t i o n

g r a d i e n t c a n b e e s t a b l i s h e d f o r t h e t r a c e p o l l u t a n t g a s , u n d e r c e r t a i n c o n d i -

t i o n s t h e m o v e m e n t o f t h e g a s w i l l b e p r o p o r t i o n a l t o t h e c o n c e n t r a t i o n g r a -

d i e n t ( F ic k s l a w o f di f fu s i on ) , a n d a s a m p l e r c a n b e d e s i g n e d t o t a k e

a d v a n t a g e o f t h is t e c h n i q u e . F i g u r e 1 6.4 il lu s t r a te s t h i s p r i n c ip l e . T h e s a m -

p l e r h a s a w e l l - d e f i n e d i n l e t , g e n e r a l l y w i t h a c y l i n d r i c a l s h a p e , t h r o u g h

w h i c h t h e p o l l u t a n t g a s m u s t d i f f u s e . A t t h e e n d o f t h e t u b e , a c o l l e c t i o n

m e d i u m r e m o v e s t h e p o l l u t a n t g a s f or su b s e q u e n t a n a l y s is a n d m a i n t a i n s a

c o n c e n t r a t i o n g r a d i e n t b e t w e e n t h e i n l e t o f t h e t u b e a n d t h e c o l l e c t i o n

m e d i u m . T h e m a t h e m a t i c a l re l a t i o n s h i p ( F i c k s l a w ) d e s c r i b i n g t h is ty p e o f

p a s s i v e s a m p l e r i s g i v e n b y

R = D A

d C

(16.1)

w h e r e R is th e r a t e o f t r a n s p o r t b y d i f f u s io n i n m o l e s p e r s e c o n d , D is th e d i f -

fu s i o n co e f f i c i en t i n s q u a re cen t i me t e r s p e r s eco n d , A i s t h e c ro s s - s ec t i o n a l

a r ea o f t h e d i f fu s i o n p a t h i n s q u a re cen t i me t e r s , C i s t h e co n cen t r a t i o n o f

s p ec i e s i n m o l e s p e r cu b i c cen t i me t e r , an d x i s t h e p a t h l e n g t h i n cen t i me t e r s .


11/15

IV Passive Sampling Systems 46 7

W e l l - d e f i n e d d i f fu s i o n t u b e

Fig. 16.4. Staticsamp ler based on the diffusion principle.

f S o l i d s o r b e n t

~ O

~ _ - h in mem berane

Fig. 16.5. Staticsampler based on the perm eation principle.

T h e a b i l it y o f g a s e s to p e r m e a t e t h r o u g h v a r i o u s p o l y m e r s a t a f ix e d r a te

d e p e n d i n g o n a c o n c e n t r a t i o n g r a d i e n t h a s b e e n u s e d t o c r e a t e s t a t i c s a m -

p le r s . Th i s p r inc ip le was o r ig ina l ly deve loped to p rov ide a s t andard ca l ib ra -

t io n s o u r c e o f t ra c e g a s b y p u t t i n g t h a t g a s in a p o l y m e r t u b e u n d e r p r e s s u r e

a n d l e t t i n g t h e m a t e r i a l d i f f u s e o r p e r m e a t e t h r o u g h t h e w a l l t o t h e o p e n

a t m o s p h e r e . P e r m e a t i o n s a m p l e r s o p e r a t e i n t h e r e v e r s e d i r e c t i o n . F i g u r e

16 .5 i l lu s tr a te s th i s type o f sys tem. A th in f i lm me m bra ne i s ope n to the

a t m o s p h e r e o n o n e s i d e a n d t o a co l le c ti o n m e d i u m o n t h e o th e r. A p o l l u t a n t

g a s i n t h e a t m o s p h e r e d i f f u s e s t h r o u g h t h e m e m b r a n e a n d i s c o l l e c t e d i n

t h e m e d i u m . T h e m a t h e m a t i c a l r e l a t i o n s h i p f o r a p e r m e a t i o n s a m p l e r i s

g i v e n b y

t

k - (16.2)

m

w h e r e k i s t h e p e r m e a t i o n c o n s t a n t, C i s t h e c o n c e n t r a t i o n o f g a s i n p a r t s p e r

mi l l ion , t i s the t ime o f exposu re , and m i s the amoun t o f gas abso rbed in

m i c r o g r a m s .

P e r m e a t i o n s y s t e m s c a n b e c a l i b r a t e d i n t h e l a b o r a t o r y a n d t h e n u s e d i n

the f ie ld for sa m ple col lec t ion for a f ixed per i od of time, e .g . , 8 h o r 7 days .

T h e s a m p l e r i s r e t u r n e d t o th e l a b o r a t o r y f o r a n a l y si s . T h e se s y s t e m s c a n b e

m a d e f o r s p e c i f i c c o m p o u n d s b y s e l e c t i n g t h e a p p r o p r i a t e c o l l e c t i o n

m e d i u m a n d t h e p o l y m e r m e m b r a n e ( 'F ab le 1 6.2 ).


12/15

6 8

1 6 A m b i e n t A i r S a m p l i n g

TABLE 16 2

Permeat ion Sam plers for Se l ec ted Gases

Gas Mem brane Sorber

Sensitivity

Chlorine Dim ethyl silicone Buffered (pH 7)

(DMS) fluorescein, 0.005

(single-backed) NaBr (0.31 )

Sulfur dioxide DMS (single-backed ) Tetrach loromercurateII)

Vinyl chloride DMS (single-backed) A ct iv at ed harcoal

(CS2 deso rption)

Alkyl lead DMS (unbacked) Silica gel (IC1 desorption)

Benzene Silicon polycarb ona te Ac tivatedcharcoal

(CS2 deso rption)

Am monia Vinyl silicone 0.6 bor ic acid

0.013ppm

(8-h exposure)

0.01 ppm

(8-h exposure)

0.02 ppm (linear

to 50ppm +)

0.2~g

0.02ppm

(8-h exposure)

0.4 ppm

(8-h exposure)

Hydroge n su lf id e DMS (single-backed) 0.02 N NaOH , 0.003M 0.01 ppm

EDTA

Hydrogen cy an ide DMS (single-backed) 0.01 N NaOH 0.01 ppm

(8-h exposure)

Source: West, P. W.,Am Lab 12, 35-39 (1980).

V S A M P L E R S I T I N G R E Q U I R E M E N T S

S a m p l i n g s it e s e l ec t io n i s d e p e n d e n t o n t h e p u r p o s e o r u se o f t h e r e s u lt s o f

t he m on i to r i ng p rog ra m . S am pl ing ac ti v it ie s a re typ i ca l ly und er t a ke n t o de t e r -

m i n e t h e a m b i e n t a i r q u a l i t y f o r c o m p l i a n c e w i t h a i r q u a l i t y s t a n d a r d s , f o r

e v a l u a t i o n o f th e i m p a c t o f a n e w a ir p o l l u t i o n s o u r c e d u r i n g t h e p r e c o n s t r u c -

t i on ph ase , fo r haz a rd eva lua t i on as soc i a ted w i th acc iden t a l sp il ls o f chem ica l s,

f or h u m a n e x p o s u r e m o n i t o r in g , a n d f o r r e s e ar c h o n a t m o s p h e r i c c h e m i c a l

a n d p h y s i c a l p r o c e s s e s . T h e r e su l t s o f a m b i e n t a i r m o n i t o r i n g c a n b e u s e d t o

jud ge t he e f fec t ivenes s o f t he a i r qua l i t y m an ag em en t a pp ro ach t o a i r po l l u t i on

p r o b l e m s . T h e f u n d a m e n t a l r e a s o n f o r c o n tr o l li n g a i r p o l l u t i o n s o u r c e s i s t o

l i m i t t h e b u i l d u p o f c o n t a m i n a n t s i n t h e a t m o s p h e r e s o t h a t a d v e r s e e ff e ct s

a r e n o t o b s e r v e d . T h i s s u g g e s t s t h a t s a m p l i n g s i t e s s h o u l d b e s e l e c t e d t o

m e a s u r e p o l l u t a n t l e ve l s c lo s e t o o r r e p r e s e n t a t i v e o f e x p o s e d p o p u l a t i o n s o f

peop l e , p l an t s , t r ees , m a t e r i a l s , s t ruc tu res , e t c . Genera l l y , s i t e s i n a i r qua l i t y

n e t w o r k s a r e n e a r g r o u n d l ev e l, t y p i c a l ly 3 m a b o v e g r o u n d , a n d a r e l o c a t e d

s o a s n o t t o b e u n d u l y d o m i n a t e d b y a n e a r b y s o u r c e s u c h a s a r o a d w a y .

S a m p l i n g s i t e s r e q u i r e e l e c t r i c a l p o w e r a n d a d e q u a t e p r o t e c t i o n ( w h i c h m a y

be as s im p le a s a fence ). A she l te r , such as a sm a l l bu i l d in g , m ay b e neces sa ry .

P e r m a n e n t s i te s r e q u i r e a d e q u a t e h e a t i n g a n d a i r c o n d i t i o n i n g t o p r o v i d e a

s ta b le o p e r a t i n g e n v i r o n m e n t f o r t he s a m p l i n g a n d m o n i t o r i n g e q u i p m e n t .


13/15

V I S a m p l i n g f o r A i r T o x i c s 469

V I S A M P L I N G F O R A I R T O X I C S

Publ ic aw areness o f the re lease o f chemica ls in to the a tmos phere has go ne

bey ond the p r im ary am bien t po l lu t an t s (e.g . SO2 o r O3) and gov ernm ent s

requ i re a i r t ox ics management p l ans . One componen t o f th i s p rocess i s t he

character iza t ion of the a i r qual i ty v ia sampl ing .

M ost of the a i rborn e chemicals c lassi f ied as a i r toxics are organic com-

po un ds wi th phys ica l and chemica l p roper t i e s rang ing f rom those s imi l a r to

fo rmaldehyde found in the gas phase to po lycyc l i c a romat i c hydrocarbons

(PAHs) w hich m ay be ab sorb ed on par t ic le surfaces . Air toxics a lso include a

nu m ber o f me ta l s and the i r com pound s . Th i s range o f vo la ti li ty and react iv -

i ty rep resen ted by a i r tox ics requ i res a va r i e ty o f sam pl ing t ec hn iq uesm from

grab sampl ing to f i l t e r t echn iques fo l lowed by ex t rac t ion and de ta i l ed

der iva t i za t ion t echn iques . W hen these com pou nds a re p resen t in the a tmos-

pher e , the con cent ra t ion level can be qui te low, in the par ts pe r b i ll ion (ppb)

to sub-ppb range fo r gases and the p i cogra m p er cub ic me te r rang e fo r pa r -

t icula te components . Two concent ra t ions must be ca lcula ted for par t ic le-

bo un d con taminan t s : t he concen tra t ions o f pa r t ic l e s in the a tmo sphere (mass

of pa r t ic l e s pe r vo lum e o f a ir ) and the conce n t ra t ion o f con tam inan t s so rbed

to the par t ic le (mass of each chemical per mass of par t ic les) . This genera l ly

requ i res ex tended sampl ing t imes and ve ry sens i t ive ana ly t i ca l t echn iques

for labora tory analysis .

The US E nvironm enta l Protection Agen cy establ i shed a p i lo t Toxics Air

Moni tor ing System network for sampl ing ambient vola t i le organic com-

pounds (VOCs) a t ppb levels in Boston, Chicago, and Houston for a 2-year

per iod [8]. Ev acu ated stainless steel canisters we re us ed to collect air at 3 cm 3

m in for 24 h . The canis ters we re re tu rned to a cent ra l labora tory and analyze d

by cryogenic concent ra t ion of the VOCs, separa t ion by gas chromatography,

and mass-se lec t ive detec t ion . This system provided informat ion on 13 VOCs

in three classes: chlorofluorocarbons, aromatics, and chlorinated alkanes.

A second sam pl ing p ro gra m in Sou the rn Ca l i fo rn ia samp led fo r po lych lo -

r ina ted d iox ins and po lych lo r ina ted d ibenzofu rans a t seven loca t ions [9 ] .

Because o f the semivo la t i l e na tu re o f these compounds , a t andem sample r

w as u sed w i th a g lass fiber fi lte r to col lec t the par t icula te-assoc ia ted com po-

nen t s fo l lowed by a po lyure thane foam so rben t t rap to co l l ec t t he vapor -

phase por t ion . These samples were re tu rned to the l abora to ry , where they

w e re e x t r ac t e d a n d a n a l y z e d w i t h h ig h - r e so lu t io n g a s c h ro m a t o g ra p h y a n d

h igh- reso lu t ion m ass spec t romet ry . The obse rved concen t ra t ions were in the

p icogram per cub ic me te r range . The t echn iques fo r these p rocedures a re

in t roduced in the next chapter .

More recen tly, i n 2001 and 2002 , the gases and dus t re l eased dur ing and

fol lowing the col lapse of World Trade Center towers as wel l as tha t found in

the a f t e rmath o f Hu rr i cane Ka t r ina in 2005 had to be ana lyzed .

Each o f these examples sugges t t ha t a i r t ox ics sampl ing i s complex and

expensive and requi res careful a t tent ion to qual i ty assurance .


14/15

4 7 16 Am bient Air Samp ling

R E F E R E N C E S

1 . P a g n o t t o , L . D . , a n d K e e n a n , R . G . , S a m p l i n g a n d a n a l y s i s o f g a s e s a n d v a p o r s , i n

The

Indus t r ia l Environmentml t s Evaluat ion and Contro l

p p . 1 6 7 - 1 7 9 . U S D e p a r t m e n t o f H e a l t h ,

E d u c a t i o n , a n d W e l f a re , U S G o v e r n m e n t P r i n t i n g O f fi ce , W a s h i n g t o n , D C , 1 97 3.

2 . T anak a , T. ,

J. Chromatogr.

153, 7-13 1978).

3 . Slan ina , J ., De W ild , P . J ., and W yers , G. P ., Ad v. Environ. S ci . Technol . 24, 129-1 54 1992).

4 . Ca d le , R. D. , The Mea surem ent o f Airborne Par t ic les. Acad em ic P r e ss , New Yo r k , 1 9 7 6 .

5. Liu , B. Y. H. ed.) ,

Fine Particles.

A c a d e m i c P r e s s , N e w Y o r k, 1 97 6.

6 . Pa lm es , E . D . , Gu n n i so n , A . F . , D iMa t to , J . , an d T o m czy k , C . ,

Am. Ind. Hyg. Assoc. J.

37,

570-577 1976) .

7. W est, P. W .,

Am. L a b .

12, 35-3 9 1980).

8 . E v an s , G . F ., L u m p k in , T . A . , Sm i th , D . L ., an d So m er v i l l e , M. C . ,

J. Air Waste Manage. Assoc.

42, 1319 -1323 1992).

9 . H un t , G . T . , an d M aise l , B. E . ,

J. Air Waste Manage. Assoc.

42, 672-6 80 1992).

S U G G E S T E D R E A D I N G

Fr i ed la n d e r , S . K . ,

Smoke D us t and Haze.

Wiley , New York , 1977 .

Her ing , S . V. ,

Air Sam pl ing Ins t rume nts for Evaluation o f Air Contam inants .

A C G I H , C i n c i n n a t i ,

OH, 1 9 8 9

Nol l , K. E . , and Mil le r , T . L . ,

Ai r Mo n i t o r i n g S u r vey Des i g n .

A n n A r b o r S c i e n c e P u b l i s h e r s , A n n

Arbor , MI , 1977 .

S tan ley - W o o d , N . G . , an d L in es , R . W . ed s . ),

Particle Size Analysis .

R o y a l S o c i e ty o f C h e m i s t r y ,

C a m b r i d g e , U K , 1 9 92 .

W i l l ek e , K . , an d Ba r o n , P . A . ,

Aerosol M easurem ent - -Pr incip les Techniques and Appl ica t ions .

V a n

N o s t r a n d R e i n h o l d , N e w Y o r k, 19 93 .

Q U E S T I O N S

1 . D e s c r i b e th e fo u r c o m p o n e n t s o f a s a m p l i n g s y s t e m .

2 . L i s t t h r e e e x a m p l e s o f t h e fo u r c o m p o n e n t s , e .g . , a m e t a l b e l l o w s p u m p .

3 . A so l id so r b en t T en ax ca r t r i d g e h a s a cap ac i ty o f 10 0 ~g o f t o lu en e . I f sam p le s w e r e co l l ec t ed

a t a r a t e o f 5 L m i n - 1, c a lc u l at e t h e m a x i m u m a m b i e n t c o n c e n t ra t i o n w h i c h c a n b e d e t e r -

m i n e d b y a n h o u r l y s a m p l e a n d a 1 5 - m i n s a m p l e .

4 . D e s c r i b e th e s a m p l i n g a p p r o a c h e s u s e d f o r ai r p o l l u t a n t s b y y o u r s t a t e o r lo c a l g o v e r n m e n t .

5 . L i s t t h e p o s s i b l e s o u r c e s o f lo s s o r e r ro r i n s a m p l i n g f o r p a r t i c u l a t e m a t t e r.

6 . W h y i s s a m p l i n g v e lo c i ty n o t a n i m p o r t a n t p a r a m e t e r w h e n s a m p l i n g fo r g a s es ?

7 . L i s t t h e a d v a n t a g e s o f p a s s i v e s a m p l i n g s y s t e m s .

8 . D e s c r ib e t h e p re c a u t i o n s w h i c h s h o u l d b e c o n s i d e r e d w h e n d e t e r m i n i n g t h e l o c a ti o n of t h e

s a m p l i n g m a n i f o l d i n l et fo r a n a m b i e n t m o n i t o r i n g s y s t e m .

9 . W h a t i s t h e c o n c e n t r a t i o n o f p a r t i c l e - p h a s e m e r c u r y i n t h e ai r i f s a m p l e s h o w s t h a t t h e a v e r-

a g e m e a n ) p a r t i c le c o n c e n t r a t i o n P M 2 . 5 ) is 1 .5 ~g m - 3 a n d t h e m e a n c o n c e n t r a ti o n o f m e r -

c u r y o n t h e p a r ti c le s i n th e s a m p l e i s 1 0 n g g - l ?

1 0. H o w i m p o r t a n t i s t h e re s t o f t h e P M f r a c t io n P M > 2 . 5 ~ m ) in t h e a b o v e s c e n a r i o ? E x p la i n .


15/15

uestions

47

11. H o w m i g h t a s a m p l e b e a n a l y z e d i n th e a b o v e q u e s t i o n s s c en a r io ( b o t h th e p a r t ic l e a n d t h e

m e t a l s s o r b e d t o th e p a r ti c le ) ? W h a t a r e t h e a d v a n t a g e s a n d d i s a d v a n t a g e s o f e ac h o f th e

m a j o r t y p e s ?

1 2. I n th e a b o v e e x a m p l e s , w h a t m i g h t b e s o m e o f th e i m p o r t a n t d i f fe r e n ce s in t h e p h y s i c a l a n d

c h e m i c a l c h a r a ct e r is t ic s b e t w e e n m e r c u r y a n d c a d m i u m i n sa m p l i n g .

13. W ha t i f you w an te d t o know a pa r t i cu l a r spec i e s o f m ercu ry (e.g. m ercu ry ch lo r ide o r non -

m e t h y l m e r c u r y ) ? C a n y o u u s e a t e c h n i q u e li k e X - r ay f lu o r e s ce n c e ? W h y o r w h y n o t ? W h a t

migh t have t o be done t o be ab l e t o answer t h i s ques t i on ; i . e . , wha t a re t he key fea tu re s

nee de d i n you r sam p l ing an d ana ly s i s plan .?

14. W ha t i s t he conce n t ra t i on o f benz o (a )p y rene (B(a )p ) i n t he scena r io i n Ques t i on 9 if i ts con -

c e n t r a t io n o n t h e p a r t i cl e s ( m e a n ) i s 1 0 p p b ? H o w w o u l d y o u c o l l ec t s a m p l e s f o r g as p h a s e

B ( a) p ? H o w m i g h t t h is d i ff e r f ro m t h e m e t h o d u s e d f o r m e r c u r y ?

cap.16 sampling

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