Show That 1 Ppm Co2 In The Atmosphere Corresponds To 2.1 Pg Carbon And Therefore That The Current Atmospheric Level Of 375 Ppm Corresponds To 788 Pg C.

- Inter-hemispheric Mixing Time

- Intra-hemispheric Mixing Time

"Boundary Layer Mixing Time lm 10 m 100 m 1km 10 km 100 km 1000 km 10,000 km Spatial Scale

FIGURE 1.4 Spatial and temporal scales of variability for atmospheric constituents.

dimensions. Four rough categories have proved convenient to classify atmospheric scales of motion:

1. Microscale. Phenomena occurring on scales of the order of 0-100 m, such as the meandering and dispersion of a chimney plume and the complicated flow regime in the wake of a large building.

2. Mesoscale. Phenomena occurring on scales of tens to hundreds of kilometers, such as land-sea breezes, mountain-valley winds, and migratory high- and low-pressure fronts.

3. Synoptic Scale. Motions of whole weather systems, on scales of hundreds to thousands of kilometers.

4. Global Scale. Phenomena occurring on scales exceeding 5 x 103 km.

Spatial scales characteristic of various atmospheric chemical phenomena are given in Table 1.1. Many of the phenomena in Table 1.1 overlap; for example, there is more or less of a continuum between (1) urban and regional air pollution, (2) the aerosol haze associated with regional air pollution and aerosol-climate interactions, (3) greenhouse gas increases and stratospheric ozone depletion, and (4) tropospheric oxidative capacity and stratospheric ozone depletion. The lifetime of a species is the average time that a molecule of that species resides in the atmosphere before removal (chemical transformation to another species counts as removal). Atmospheric lifetimes vary from less than a second for

TABLE 1.1 Spatial Scales of Atmospheric Chemical Phenomena

Phenomenon

Length scale, km

Urban air pollution

1-100

Regional air pollution

10-1000

Acid rain/deposition

100-2000

Toxic air pollutants

0.1-100

Stratospheric ozone depletion

1000-40,000

Greenhouse gas increases

1000-40,000

Acrosol-climate interactions

100-40,000

Tropospheric transport and oxidation processes

1^0,000

Stratospheric-troposphcric exchange

0.1-100

Stratospheric transport and oxidation processes

i ^0,000

the most reactive free radicals to many years for the most stable molecules. Associated with each species is a characteristic spatial transport scale; species with very short lifetimes have comparably small characteristic spatial scales while those with lifetimes of years have a characteristic spatial scale equal to that of the entire atmosphere. With a lifetime of less than 0.01 s, the hydroxy! radical (OH) has a spatial transport scale of only about [cm. Methane (CH4), on the other hand, with its lifetime of about 10 years, can become more or less uniformly mixed over the entire Earth.

The spatial scales of the various atmospheric chemical phenomena shown above result from an intricate coupling between the chemical lifetimes of the principal species and the atmosphere's scales of motion. Much of this book, will be devoted to understanding the exquisite interactions between chemical and transport processes in the atmosphere.

I Units of Atmospheric Emission Rates and Fluxes Fluxes of species into the atmosphere are usually expressed on an annual basis, using the prefixes given in Table A.5. A common unit used is teragrams per year, Tg yr_1 (ITg = 10l2g). A11 alternative is to employ the metric ton (11 = 106g = 10' kg). Carbon dioxide fluxes are often expressed as multiples of gigatons, Gt (lGE=109t=l 10»g=lPg).

PROBLEMS

1.1A Calculate the concentration (iri molecules cm-'1) and the mixing ratio (in ppm) of water vapor at ground level at T — 298 K at RH values of 50%, 60%, 70%, 80%, 90%, 95%, and 99%.

1,2A Determine the concentration (in jig m~3) for N20 at a mixing ratio of 311 ppb at p= latm and T = 298 K.

1.3a A typical global concentration of hydroxyl (OH) radicals is about 106 molecules cm 3. What is the mixing ratio corresponding to this concentration at sea level and 298 K?

1.4a Measurements of dimethyl sulfide (CH3SCH3) during the Aerosol Characterization Experiment-1 (ACE-1) conducted November-December 1995 off Tasmania were in the range of 250-500 ngm I Convert these values to mixing ratios in ppt at 298 K at sea level.

1.5a You consume 500 gallons of gasoline per year in your car (lgal = 3.7879 L). Assume that gasoline can be represented as consisting entirely of CgH18. Gasoline has a density of 0.85 g cm-3. Assume that combustion of CgH18 leads to C02 and H20. How many kilograms of C02 does your driving contribute to the atmosphere each year? (Problem suggested by T. S. Dibble.)

1.6a Show that 1 ppm C02 in the atmosphere corresponds to 2.1 Pg carbon and therefore that the current atmospheric level of 375 ppm corresponds to 788 Pg C.

REFERENCES

Bentley, C. R. (1997) Rapid sea-level rise soon from West Antarctica Ice Sheet collapse? Science 275, 1077-1078.

Holton, J. R., Haynes, P. H., Mclntyre, M. E„ Douglass, A. R., Rood, R. B„ and Pfister, L. (1995) Stratosphere-troposphere exchange, Rev. Geophys. 33, 403-439.

Intergovernmental Panel on Climate Change (IPCC) (2001) Climate Change 2001: The Scientific Basis, Cambridge Univ. Press, Cambridge, UK.

Kasting, J. F. (2001) The rise of atmospheric oxygen, Science 293, 819-820.

Meehl, G. A., and Tebaldi, C. (2004) More intense, more frequent, and longer lasting heat waves in the 21st Century, Science 305, 994-997.

Trenberth, K. E., and Smith, L. (2005) The mass of the atmosphere: A constraint on global analyses, J. Climate 18, 864-875.

Walker, J. C. G. (1977) Evolution of the Atmosphere, Macmillan, New York.

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Responses

  • kalevi
    What is global warming in atmospheric chemistry?
    9 years ago
  • pauliina
    What are the charastics of atmospheric chemicals?
    9 years ago
  • casey
    What ppm/K correspondes to?
    1 year ago

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