11 Control of sulfur oxide The control of particulates and VOCs is mostly accomplished by physical processes(cyclones, ESPs, filters, leakage control, vapor capture, condensation)that do not involve changing the chemical nature of the pollutant. Some particles and vOCs are chemically changed into harmless materials by combustion. This chapter and the next concern pollutants--sulfur oxides and nitroger oxides that cannot be economically collected by physical means nor rendered harmless by combustion. Their control is largely chemical rather than physical. For this reason, these two chapters are more chemically oriented than the rest of the book. Sulfur and nitrogen oxides are ubiquitous pollutants, which have many sources. SOz, SO, and NO are strong respiratory irritants that can cause health damage at high concentrations. We have NAAQS for SO and NO2. The states are required to prepare SIPs for the control of NOz and so. These gases also form secondary particles in the atmosphere, contributing to our PMio and PM25 problems and impairing visibility. They are the principal causes of acid rain. The Clean Air Act of 1990, Section 401-Acid Deposition Control, requires substantial reductions in our national emissions of both sulfur and nitrogen oxides over the next few decades 11.1 The Elementary Oxidation-Reduction Chemistry Of Sulfur And Nitrogen are significantly different, but their chemistry is quite similar, as this short section showsmethods This chapter concerns sulfur oxides; the next, nitrogen oxides. Their sources and control Both sulfur and nitrogen in the elemental state are relatively inert and harmless to humans. Both are needed for life, all animals require some N and s in their bodies. However, the oxides of sulfur and nitrogen are widely recognized air pollutants. The reduced products also are, in some cases, In parallel form, the oxidation and reduction products of nitrogen and sulfur. Reduction means the addition of hydrogen or the removal of oxygen. If we reduce nitrogen, we produce ammonia (which logically should be called hydrogen nitride, but because it had a common name before modem chemical naming systems were devised, it goes by its common name, ammonia). Similarly if we reduce sulfur, we produce hydrogen sulfide. Both hydrogen sulfide and ammonia are very strong-smelling substances, gaseous at room temperature (-60'C and. C boiling points, respectively ) and toxic in high concentrations.(High concentrations due to accidental releases often cause fatalities. These occur in the production and use of ammonia as a fertilizer and refrigerant and in the production and processing of"sour"gas and oil, which contain hydrogen ulfide. Neither ammonia nor hydrogen sulfide has been shown to be toxic in the low concentrations that normally exist in the atmosphere hen nitrogen is oxidized, nitric oxide(NO)and then nitrogen dioxide(noz) form; likewise sulfur forms sulfur dioxide(SO2)and then sulfur trioxide (so3). These are all gases at room temperature or slightly above room temperature( boiling points 21C, 34. C,-10'C, and 45C respectively ) The oxides have higher boiling points than the hydrides. Both nitrogen and sulfur can also form other oxides, but these are the ones of principal air pollution interest In the atmosphere NOz and SO3 react with water to form nitric and sulfuric acids, which then react with ammonia or any other available cation to form particles of ammonium nitrate or sulfate or some other nitrate or sulfate. These particles, generally in the 0. 1 to l-H size range, are very efficient light-scatterers they persist in the atmosphere until coagulation and precipitation remove them. They are significant contributors to urban PM1O and PM2.5 problems. They are the principal causes of acid deposition and of visibility impairment in our national parks. NO and NO2 also play a significant role in the formation of o The estimated concentrations of these materials in unpolluted parts of the worlds atmosphere are SO2, 0.2 ppb; NH3, 10 ppb; NOz, I ppb 11.2 An Overview of the sulfur problem l1-111－1 11 Control of Sulfur Oxides The control of particulates and VOCs is mostly accomplished by physical processes (cyclones, ESPs, filters, leakage control, vapor capture, condensation) that do not involve changing the chemical nature of the pollutant. Some particles and VOCs are chemically changed into harmless materials by combustion. This chapter and the next concern pollutants--sulfur oxides and nitrogen oxides that cannot be economically collected by physical means nor rendered harmless by combustion. Their control is largely chemical rather than physical. For this reason, these two chapters are more chemically oriented than the rest of the book. Sulfur and nitrogen oxides are ubiquitous pollutants, which have many sources. SO2, SO3, and NO2 are strong respiratory irritants that can cause health damage at high concentrations. We have NAAQS for SO2 and NO2. The states are required to prepare SIPs for the control of NO2 and SO2. These gases also form secondary particles in the atmosphere, contributing to our PM10 and PM2.5 problems and impairing visibility. They are the principal causes of acid rain. The Clean Air Act of 1990, Section 401--Acid Deposition Control, requires substantial reductions in our national emissions of both sulfur and nitrogen oxides over the next few decades. 11.1 The Elementary Oxidation-Reduction Chemistry Of Sulfur And Nitrogen This chapter concerns sulfur oxides; the next, nitrogen oxides. Their sources and control methods are significantly different, but their chemistry is quite similar, as this short section shows. Both sulfur and nitrogen in the elemental state are relatively inert and harmless to humans. Both are needed for life; all animals require some N and S in their bodies. However, the oxides of sulfur and nitrogen are widely recognized air pollutants. The reduced products also are, in some cases, air pollutants. In parallel form, the oxidation and reduction products of nitrogen and sulfur. Reduction means the addition of hydrogen or the removal of oxygen. If we reduce nitrogen, we produce ammonia (which logically should be called hydrogen nitride; but because it had a common name before modem chemical naming systems were devised, it goes by its common name, ammonia). Similarly, if we reduce sulfur, we produce hydrogen sulfide. Both hydrogen sulfide and ammonia are very strong-smelling substances, gaseous at room temperature (-60。C and -33。C boiling points, respectively), and toxic in high concentrations. (High concentrations due to accidental releases often cause fatalities. These occur in the production and use of ammonia as a fertilizer and refrigerant and in the production and processing of "sour" gas and oil, which contain hydrogen sulfide.) Neither ammonia nor hydrogen sulfide has been shown to be toxic in the low concentrations that normally exist in the atmosphere. When nitrogen is oxidized, nitric oxide (NO) and then nitrogen dioxide (NO2) form; likewise, sulfur forms sulfur dioxide (SO2) and then sulfur trioxide (SO3). These are all gases at room temperature or slightly above room temperature(boiling points 21。C, 34。C, -10。C, and 45。C, respectively). The oxides have higher boiling points than the hydrides. Both nitrogen and sulfur can also form other oxides, but these are the ones of principal air pollution interest. In the atmosphere NO2 and SO3 react with water to form nitric and sulfuric acids, which then react with ammonia or any other available cation to form particles of ammonium nitrate or sulfate or some other nitrate or sulfate. These particles, generally in the 0.1 to 1-μ size range, are very efficient light-scatterers; they persist in the atmosphere until coagulation and precipitation remove them. They are significant contributors to urban PMl0 and PM2.5 problems. They are the principal causes of acid deposition and of visibility impairment in our national parks. NO and NO2 also play a significant role in the formation of O3. The estimated concentrations of these materials in unpolluted parts of the world's atmosphere are SO2, 0.2 ppb; NH3, 10 ppb; NO2, 1 ppb. 11.2 An Overview of the Sulfur Problem