Problems

1. Measuring air pollution due to particles by mass can be quite misleading in terms of their ultimate impacts, for example on health. For example, the results of some laboratory studies show that ultrafine particles cause inflammatory responses while larger particles with the same chemical composition do not. Calculate how many particles with diameter 0.2 /¿m would need to be collected on a "hi-vol" sampler (which is essentially just a filter) to have the same mass as one particle of diameter 20 /jlm. Assume they have the same chemical composition and hence equal densities.

2. Derive the relationship between 1 ppt at 298 K and 1 atm pressure and the concentration of a species in jxgm-3 from first principles.

3. The most stringent 1-h AQS for CO shown in a review of such standards by Cochran et al. [J. Air Waste Manage., 42, 1567 (1992)] is 15,000 ¡xg m~3 (Canada) and the least stringent is 40,000 ¿ig 3 (adopted by a number of countries, including the United States). What is this range of AQS in units of ppm?

4. Free radicals such as OH are present in such small concentrations that their concentrations are frequently given in units of molecules cm~3 rather than ppm, ppb, etc. A typical OH concentration in the lower troposphere is 5 X 105 radicals cm"3. What is this concentration in terms of the mixing ratio unit ppt, assuming 298 K and 1 atm pressure?

5. You measure an air temperature of 260 K at a pressure of 600 mbar. What is the potential temperature, assuming a reference pressure of 1000 mbar?

6. An air parcel has a temperature of 7°F and a pressure of 450 Torr. What is its potential temperature (6) if the reference pressure is 1 atm? Take cp for air to be 29.1 J K"1 mol"1.

7. Using the dry adiabatic lapse rate, by how much would you expect the temperature to change from the earth's surface to an altitude of 1000 feet, which, as seen in Fig. 2.19, sometimes corresponds to the bottom of the inversion layer in the Los Angeles area?

8. Estimate the mass of the atmosphere, given that the area of the surface of the earth is about 5.1 X 1014 m2. Assume a uniform pressure of 1 atm at the earth's surface. Compare this to the mass of the earth itself, 6.0 X 1024 kg.

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