Figure 1: The basic atmospheric chemistry of tropospheric ozone formation. 10 Spray April 2016 Pressure Points Doug Fratz CSPA Aerosol Products Division Staff executive It is a remarkable coincidence: the two serious issues that have most impacted the aerosol products industry are both related to ozone. The first is associated with stratospheric ozone, the second involved tropospheric (ground-level) ozone. Ozone is the form of oxygen that’s essential in the stratosphere, protecting us from hazardous ultraviolet radiation, but damaging in the troposphere to both people and vegetation. The first ozone crisis involved chlorofluorocarbons (CFCs) and the next involved volatile organic compounds (VOCs). Complex atmospheric science is behind these billion-dollar issues. In 1974, scientists found that the CFCs being used as refrigerants, foam blowers and aerosol propellants might eventually deliver chlorine to the stratosphere and deplete ozone. Half of U.S. aerosol products used CFC propellants, and half of CFC usage was for aerosol products. Congressional hearings began immediately, and so did the decline in aerosol product sales. There were more than 2.9 billion aerosol products filled in 1973; by 1982 it was 2.1 billion.1 The Chemical Specialties Manufacturers Association’s Aerosol Division formed the Council on Atmospheric Science to study the science. By 1975, companies began reformulating products in anticipation of a 1978 ban. The U.S. Environmental Protection Agency (EPA) later found that the U.S. aerosol industry impact was more than $1 billion to eliminate CFCs. The aerosol industry demonstrated admirable tenacity to survive. The atmospheric science behind stratospheric ozone depletion is relatively simple. Stratospheric ozone is formed by high-energy solar particles splitting oxygen molecules (O2) to create ozone (O3). Chlorinated hydrocarbons with long atmospheric half-lives can diffuse up into the stratosphere where those same high-energy particles lead to chlorine radicals that steal one of the oxygen atoms from O3, thereby depleting ozone concentrations. Atmospheric Science: A Tale of Two Ozones In contrast, the formation of tropospheric ozone involves complex reactions involving nitrogen oxides (NOx), organic gases (VOCs), sunlight and the hydroxyl radical (OH.). A simplified version of that chemistry can be seen in Figure 1. The basic engine of ozone formation involves NOx, which with sunlight creates ozone when nitrogen dioxide (NO2) oxidizes O2 to O3. VOCs (represented by R in Figure 1) are initiated into the photochemistry when they react with OH. and recreate NO2, thus forming more O3. VOCs can also terminate radicals and remove NOx, which lowers ozone. A simple way of looking at the atmospheric chemistry is that NOx is the engine and VOCs are the fuel. The VOC issue emerged in the 1980s when the aerosol industry was still recovering from the stratospheric ozone issue, and began affecting the industry in the late 1980s as California, other states and EPA began requiring lower VOCs in consumer products. The impact of VOC regulations has, in some ways, equaled that of CFCs. Companies have had to reformulate more than half of their products at costs exceeding $1 billion. The key differences are that the product reformulations have occurred over 25 years—not two or three—and have not resulted in loss of products. Lessons learned in the 1970s have allowed the aerosol industry to manage the VOC issue far more successfully. It is also important to note that in the VOC crisis, both time and the basic atmospheric chemistry work in the industry’s favor. The science of tropospheric photochemistry has evolved with increasing clarity that: 1) Specific VOCs vary greatly in ability to assist ozone formation (photochemical reactivity); 2) major reductions in NOx are required to attain healthy ozone levels; and 3) as NOx emissions are reduced, overall VOC reactivity is reduced. All three of these factors are inherent to the equations in Figure 1. Dr. William Carter of the University of California, Riverside created the Maximum Incremental Reactivity (MIR) scale to estimate relative MIR—the increase in ozone under atmospheric conditions most favorable to VOCs increasing ozone. (The majority of VOCs in consumer aerosol products has low reactivity, and thus, has limited impact on ozone formation.) Before 1990, ozone attainment strategies focused solely on VOC reductions, since the high NOx levels made VOC reductions more effective. The science somewhat ironically demonstrates that if the ratio of VOCs to NOx is relatively low, only VOC reductions lower ozone, but if the ratio is reversed, only NOx reductions work.2 continued on p.37
Spray April 2016
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