Ozone ground-based measurements by the GASCOD near-UV and ...

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Terra. Nova. Bay station in. Antarctica. (74.6°S,. 164.6°E) during the summer expeditions. 1988-1990 of. PNRA. (PNRA is the national research program in.
N95- 11071

OZONE

GROUND-BASED

MEASUREMENTS

G. Giovanelli,

BY

P. Bonasoni,

CNR

-

the

"GASCOD"

M. Cervino,

FISBAT

GASCOD,

a

differential

near-ultraviolet

optical

and

spectrometer,

was

measurements

taken

program di Ricerche coincident in

the

same

visible

area

presented, as is another comparison performed Italy. Also introduced is an updated model solar zenith measurements taken from ground-based, which was campaign 13.1°E)

upward-looking employed for

at Are-Ostersund during EASOE

2.

is in for a

in of

remote the

no knowledge measurement,

calibration without need A DOAS spectrometer Vis spectral regions diode-array sensors a multi-wavelength measurements spectrometer, spectrometer zenith solar

as

made with called correlating radiation,

GASCOD

and

its

data

spectraI dispersion DOAS method for data method in the

values [I] and analysis [4]. remote-sensor

radiation scattered alon E the zenith. spectrometer features a Jobin-Yvon

holographic

spherical

is about detector

cm in length. 0.12 nm/diode O.S run.

the is

grating

The

with

same as the a Hamamatsu

a

input PCD

format: and the

each plxel of array is 2.54

The spectral dispersion and the overall optical

grating

can

be

moved

by

throughput

telescope's. linear diode

is about resolution

a stepper

motor,

and an internal H E lamp is used for wavelength calibration each time the motor moves the gratlng:the spectrum is held to be calibrated only when its two highest values match the position of the array detector's two central

of the unattenuated which is very useful

absorbers with high and high-precision

diodes. spectral

for a reference gas. working in the UV and can use the linear

method

of multiple and specificity

the same the same DOAS

array detector with Ix512 the array is 0.050x2.5 mm

atmospheric sensing. Other advantages DOAS approach include simultaneous

determination sensitivity

of

solar light The GASCOD

that The

regions via differential optical spectroscopy (DOAS). The basic between the differential and absolute methods is that the former, unlike the requires during

description

The very narrow field of view of the input optics (a Cassegraln telescope featurin E 1500 /am focal length and 300 mm diameter) provides the best approximation of the atmospheric transfer equation model for the interpretation of the

A wide range of atmosphere trace Eases, including 03, NO2, OCIO, NO3, BrO, HN02, CH20, S02 and OH can be detected in the UV and visible

latter, spectrum

in laboratory presented and

configuration is used with the atmospheric transfer model to interpret zenith diffuse solar spectrum measurements.

(63.3°N, Arctic

Introduction

spectral absorption difference absorption

F. Ravegnani

ITALY

Stepwise analysis

have use The

Stratospheric Ozone Experiment). The GASCOD can examine the spectra from 300 to 700 nm, in 50 nm steps, by movin E the spectrometer's grating. At present, it takes measurements of solar zenith radiation in the 310-342 nm range for 03 and in the 405-463 nm range for NO2. 1.

SYSTEM

The IX)AS system was developed in two configurations: the GASCOD (fig. l), a groundbased remote sensor for measuring direct and diffuse solar radiation [1, 2], and the l-meter multi-path configuration (fig. 2) to measure absolute gas cross-sections [3]. Both versions

GASCOD spectrometer, the 1991-92 winter in Sweden (European

and

DOAS

developed

in Antarctica, in Antartide"). 03 total column Antarctic

Bologna,

VISIBLE

absorption cross-sections measured by a multi-path spectrometer are discussed.

at CNR's FISBAT Institute in Bologna, Italy, and first tested at Terra Nova Bay station in Antarctica (74.6°S, 164.6°E) during the summer expeditions 1988-1990 of PNRA (PNRA is the national research "Programma Nazionale A comparison with

AND

F. Evangelisti

Institute.

ABSTRACT

NEAR-UV

is I.

a detector, thus becomln E device. The data from

This makes accuracy Our spectral during zenith

based The

on the measurement

spectrum

such a UV/Vis diode-array GASCOD (gas-absorptlon optical differences) for and the 03 dlfferentlal

2.

707

(Is)

The measurement (Io) inferred (solar spectrum or background

it of

possible nm.

to

interpretation solar radiation

following of as

0.2

the

recorded

of from at diffused

the

steps: solar by

ensure

a

of the DOAS measurements zenith the

scattered spectrometer.

sun reference the Langley-plot the top of the solar spectrum

spectrum method atmosphere Ib).

sp l'_rlc_l

mirrors

_¢ Fig.2

Multipoth

Cell Spec_ometer

I,(A)

lo(A)

GASCOD

and

set-up

Is(A)

Laboratory

measurement

of

the

to

"b"

g=0,

cross-sectlons

either

wlth

the

used

identical

in

field

characteristics

or

to

analytical

....

into

followlng

one

having

there

employed

can

Spectral

B.

it

recorded

Smoothing:

It

square

is

the

by

are

cross-sections

applied

to

all Tg

via

non-linear

analysis

(or

in

procedures)

the

absorption

differential

cross-sections

other

values

of

by

regression

D.

Shift

&

subtracting

function

the

from

laboratory-measured applied

to

atmospheric ratio

all

to

their

Regression

so

It

ailgned

as

regression

analysis:

to

features

to

the

(step

of

solar

regression

means

analysis

of

atmosphere

given

in

50

into

minimizing

the

of

the

column

value

residual

regression

of

the

the &

of

the

of

the

can

absorbers'

yield

slant

the

columns.

SOS,

we

used

the

To

procedure

Stretch"whlch

removes

slight

of

spectral

of

I=/-i-_s

in

respect

to

Io/-T_

Intensity-weighted

optical

the

least

to

by

an

gas

is

normally

of

I

account

computation:

to

overcome

model

solar

of

for

radiation

the

the

atmospheric

interpreting

the

zenith

measurements.

atmospheric Air-mass

the

km

only

used

difficulties

transfer

square

parameterizlng

layers

path

narrow

each

the

factor:

vertical

the

it

column

is

computed

amounts

of

to

determine

the

absorbers

and under

taking

slant

spectrum of

linear

applied

equation

the

absorber.

(SOS)

displacement

F. transfer

g-th

I) the

the

zenith

cross-section

by

_R

function.

the

differential analyzed

for and

and

0, I,2,..,n of

calculation being

cross-sectlon scattering),

is

determine

correlation of

=

squares

values

it ratioed

(Mie

least-square

best

£. C.

_o

their

values; the

spectra

g

Stretch:

of

"Shift also

as Rayleigh

the

minimize absolute,

such for

the

of

linear analyzed

resulting

vx particle

abundance

sum belnE

the

non-gas

trace,

cross-sectlon),

with

least

applying

smoothing

gases

Among

several

cross-section

large

(Ring

instrument.

determines

regression

absorption

gas.

steps:

alignment:

spectra

the

g-th

be the

A.

is

the

it.

procedure

the

n

of

scattering), dlvlded

of

computed

procedure,

I,2

(molecular The

values

same _g(A)

spectrometer

smoothed respectively

absolute cross-sectlon

absorptlon

the

ground,

the

I=(A)

point

with

along

the

are

and

via _g(A)

3.

scattered

path

lo(k) F_.I

configurotion

lrradlance

the vertical

_ C Om )uter

investigation.

single In

ground-based

measurement

of

zenith

scattering: scattered Is

Io

Is

be

n

I

Z

Io

the lo(A)

supplies value is

of the

density

after the

gas

several slant

incident at

the

solar top

of

and

_z

where:

is

=

I

the flux

into

of range

the

708

nm 03 for

be

simplified

into

50

The

the

NO2

by

slant

for

layers, used

instead

column

employs

the and

The the

atmospheric

study

amounts

the

dividing

Our

is

range

column

can

of

path.

spherical

present

spectral slant

vertical

summation

flux

value

layers.

the

integral.

310-342

atmosphere,

the

equal

thick;

intensity the

along

divided

km

the

integrating

can

atmosphere

radiation the

flux

calculations

simplifications column

by

radiation

g=1

radiation

calculated

model which

solar

each of the

determination the

amounts.

405-463

run

4OO

3OO

,o o c>

2OO

100

I,*,l,,,t.,,i.,,i,,,i,,,i,,.t 13

17

21

25

29 '1

3

7

11

1989

Ozone the

Terra

Nova

[GASCOD]

x

Terra

Nova

[TOMS]

+

South

Pole

[DOBSON]

..,I,,*l.,.I,.'.l,..I.=,l,,,i,,,i.,,l..,i,=,l,,.i,,.i,,.i

November

Fig.3



vertical

some

15

19

23

27

31 I

_,

8

12

column

end

24-

January

amounts area

20

os by

28

1

5

I

December

Antarctic

16

measured

Dobson

by

1990

GASCOD

spectrometer

February

and

at

TOMS

South

in

Pole.

35

30 3.

Data

Comparlson

The

GASCOD

(74.6°S,

was

42

4

Bay

on

1989-90

km

the

of

TOMS

station.

The

between

and,

given acceptable

the

trend

overall

values,

between

The

the

detailed

GASCOD

of and

TOMS

farmer's

values

underestimated: in

76X

of

lack

of

fact

that

first

the

cases

the

is

in

the

linear program,

1991

column

data

those

taken

deployed

297

the

other

201

of

in

figure

of

WODC.

60

km The 5;

and

DUs

by

from

the

distribution

TOMS

of

dotaset

in

differences

figure

3.

the

o

25

DUs)

16X.

here

* z_

A

0

0

This to

the

for

the

upgraded

its was

,o, _1

0

03 at

data too,

during

Bologna

near

Ozone

Data at

sets

are show

z_ C,ASCO0

[Bologna]

and

,_ DOBSON [SPC-VVODC

one

o 1_

Bologna,

Center,

Sestola,

they

0

vertical

spectrometers:

Capofiume

Bologna

0

to MOS

repeated

GASCOD

World

as

computational

the

Dobson

compared here,

of and

the

(Hamamatsu

in

the

Pietro the

analysis GASCOO

the

shows

in

used

between

two

Frequency between

of

(average

was

comparison

by San

Fig.4

in

readlnEs.

device

Italy

recorded

at

station

the in

[RZR311K;K_ (DU)

an

Dobson

attributable

GASCOD

array}

and

March

Kx_ K,x>

systematically

being

detection

diode

KX>

10

03

especially

than

the

the of

(Version

frequency

distribution

the

difference

GASCOD

and

shows

same

at

agreement, rather

Terra

KX KX KX