Introduction to Atmospheric Chemistry Measurements-I

John OrtegaNational Center for Atmospheric ResearchBoulder, CO, USA

National Center for Atmospheric ResearchBoulder, CO USA

United StatesNational Science Foundation

Outline

• Atmospheric structure (T, P)• Atmospheric composition (What’s in the air?)• Emissions (Where do things come from?)• Atmospheric lifetime (How long does it exist?)• Chemistry (How do things react?)

• Ideal gas law: PV=nRT; n=PV/RT = 2.4 x 1019 molecules cm-3 at the surface

• Pressure = weight of atmospheric column above a surface

• ~101 kN/m2 or 1 kg/cm2 or 14.7 lb/in2

• Gamma (G) = atmospheric lapse rate = cooling rate with increased altitude in °C km-1

• Dry: 10• Wet: 4• Average: 6-8

• Free troposphere – layer of the atmosphere that is not affected by the surface and winds are geostrophic (parallel to isobars)

• Boundary layer – layer below which is affected by the surface; affected by vertical motion due to radiative heating.

• How does the boundary layer change with different times of day?

Planetary Boundary LayerWinds are geostrophicParallel to isobars

Surface (friction) influences , vertical motion due to radiative heating

½ atmosphere = ?

StructureG = -g/Cp = -9.8 K/km (dry)

Which is which?

DryWetAverage

Composition: What’s in the air?

Approximate lower tropospheric mixing ratios

This is what we concentrate on!CO2, CO, CH4, VOC, oVOC, NOx, SO2

Challenge: How to measure one compound among many?

SO2

SO2

SO2

CO2

SO2

CO2

SO2

SO2

CO2

CO2

CO2

O3

O3

O3

O3

O3

O3

O3

NOx

NOx

NOx NOx

NOx

NOx NOx

NOx

CH4

CH4 CH4

CH4 CH4

CH4

CH4

CH4 CH4

CH4

C5H8 C6H6

C6H6

C6H6

C6H6

C5H8

C5H8

C5H8

C5H8

C5H8

CH4

CO

CO CO

CO

CO

CO

CO

CO

SO2

SpecificityInterferenceRemote vs. DirectDerivitizationOther practical issues

Huge range of sizes (~2 nm – 10 mm)

Non-refractory aerosol composition (PM1 or PM2.5 from AMS)

Jimenez et al. 2009

Data courtesy of C. Liousse and E. Assamoi.

Direct emissions relevant to Nigeria II

COVOCoVOCNOxPM (EC, POA)

O3SOA

Approximate budget of 2 compounds in Tg per year• CO CH4

D. Jacob: http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap11.html

Approximate atmospheric lifetimes

1 hr~1 s

How are compounds removed from the atmosphere?

Oxidation• NO3• OH• O3

1 Chemistry Example – Leighton Cycle

NO + O3 → NO2 + O2NO2 + hn → NO + OO+O2+M → O3---------------------------------

l < 420 nm

Nitr

ogen

Oxi

des

(NO

x)

Volatile Organic Compounds (VOCs)

Ridge: Optimum O 3 production

~100 ppb

~ 1 ppm

O3 is a non-linear function of NOx and VOCs

VOC-limited

NOx-limited