Introduction to Atmospheric Chemistry Measurements-I John Ortega National Center for Atmospheric Research Boulder, CO, USA National Center for Atmospheric Research Boulder, CO USA United States National 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?)

Structure Ideal gas law: PV=nRT; n=PV/RT = 2.4 x molecules cm -3 at the surface Pressure = weight of atmospheric column above a surface ~101 kN/m2 or 1 kg/cm 2 or 14.7 lb/in 2 Gamma (  ) = 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 Layer Winds are geostrophic Parallel to isobars Surface (friction) influences, vertical motion due to radiative heating

½ atmosphere = ?

Structure  = -g/C p = -9.8 K/km (dry)

Which is which? Dry Wet Average

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 CO2 SO2 CO2 SO2 CO2 O3 NOx CH4 C5H8 C6H6 C5H8 CH4 CO SO2 Specificity Interference Remote vs. Direct Derivitization Other practical issues

Huge range of sizes (~2 nm – 10  m)

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 CO VOC oVOC NOx PM (EC, POA) O3 SOA

Approximate budget of 2 compounds in Tg per year CO CH4 D. Jacob:

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 + O2 NO2 + h → NO + O O+O2+M → O < 420 nm

Nitrogen Oxides (NOx) Volatile Organic Compounds (VOCs) Ridge: Optimum O 3 production ~100 ppb ~ 1 ppm O 3 is a non-linear function of NOx and VOCs VOC-limited NOx-limited