Acid Rain (PowerPoint) PDF

Air Pollution Regulations Clean Air Act – US Federal Law. Enforced by the EPA to “develop and enforce regulations to protect the general public from exposure to airborne contaminants”. Establishes the National Ambient Air Quality Standards (NAAQS) Pollutant Type Averagi...

Air Pollution Regulations Clean Air Act – US Federal Law. Enforced by the EPA to “develop and enforce regulations to protect the general public from exposure to airborne contaminants”. Establishes the National Ambient Air Quality Standards (NAAQS) Pollutant Type Averaging Time Standard SO2 Primary 1 hour 75 ppb CO Primary 8 hours 9 ppm CO Primary 1 hour 35 ppm O3 Secondary 8 hours 0.070 ppm NO2 Primary 1 hour 100 ppb PM2.5 Primary & Secondary 24 hours 35 µg m-3 1 year 15.0 µg m-3 Ozone Standards 201 4 Practical Ways of Reducing Ozone in the Troposphere Reduce level of reactants i.e. NOx, VOCs (hydrocarbons) Most common - reduce hydrocarbons but in many urban areas, NOx determines rate of reaction Caveat: High hydrocarbons from natural sources, deciduous trees emit highly reactive terpenes [e.g., isoprene] Lower temp of combustion (less NOx) Catalytic converters effective in removing 80-90% of hydrocarbons + CO + NOx from auto exhaust Correct air fuel mixture Have strategies worked in the US? Indianapolis, IN Los Angeles, CA Obama era clean air act “Clean air” - 20-40 parts per billion (ppb) >150 ppb - acute headache 𝟏 𝐩𝐩𝐛 = >250 ppb - acute chest pain, sore throat, cough 𝟏 , 𝟎𝟎𝟎 ,𝟎𝟎𝟎 , 𝟎𝟎𝟎 12/07/2024 5 Long-Term Trends in Ozone Concentrations National West Southeast Global Changes in NOx Emissions Relative to emissions in 2005 Increase in NOx emissions in India and China Decrease in United States and marginal decrease in Europe and Southern Africa K. Miyazaki et al.: Surface NOx emissions 2005–2014, Atmos. Chem. Phys. Tropospheric Chemistry is a Global Issue Pollution exports Emissions in one location don’t affect air quality in just that location. Global Transport Affects Ozone Locally One study finds that ~65% of the ozone in the Western US can be attributed to long-range transport from Eastern Asia Rising polluted air from East Asia is transported long-range in the free troposphere (i.e., above cloud level) across Pacific Ocean As air mixes downward over land (continental US), ozone is transported to near surface M. Lin et al.: US surface ozone trends and extremes from 1980 to 2014, Atmos. Chem. Phys. 2017 What goes up must come down: Acid rain – formation, effects, and remediation Acid rain kills plant life, pollutes rivers and streams, and erodes stone/rock pH of “Acid Rain” pH of unpolluted rain is ~5.6 due to dissolved CO2, forming carbonic acid CO2(g) + H2O  H2CO3(aq) H2CO3(aq) ↔ H+(aq) + HCO3-(aq) Acid rain pH is less than 5 and comes (primarily) from: SO2(g) + H2O(l)  H2SO3(aq) SO3(g) + H2O(l)  H2SO4(aq) 2NO2(g) + H2O(l)  HNO2(aq) + HNO3(aq) Effects of Acid Rain Acidification results in: Decrease in plant growth in lakes and streams Decrease in dissolved organic carbon from plant productivity in lakes and streams Increase in [Al3+] in lakes and streams, and in fish Leaching of Ca2+, K+, and Mg2+ Few fish survive below pH of 5 Severe effect on trees; dieback from altered nutrient uptake A Problem-Solving Approach to Aquatic Chemistry, J. N. Jensen, p. 317, Copyright (2003) Why acid rain is corrosive? Corrodes metals and carbonates via oxidation Fe(s) + 2H+(aq)  Fe2+(aq) + H2(g) CaCO3(s) + 2H+(aq)  Ca2+(aq) + CO2(g) + H2O(l) Regional differences in acid rain Major contributors to acid raid: Sulfur Dioxide (SO2) Sulfur dioxide is produced by volcanoes and by the oxidation of various sulfur- containing gases produced by the decomposition of plants The main anthropogenic source of SO2 is the combustion of coal SO2 Emissions from Combustion and Industry Coal combustion: 1-6% of coal is sulfur, >50% of which is FeS2 (iron sulfide) 4FeS2 + 11O2  2Fe2O3 + 8SO2 Crude oil is 1-3% sulfur Non-ferrous smelting: 2NiS(s) + 3O2(g)  2NiO(s) + 2SO2(g) Global sulfur dioxide (SO2) concentrations Fossil-Fuel Combustion and Industry 70 Tg (S) yr-1 Biomass Burning 2.8 Tg (S) yr-1 Volcanoes 7-8 Tg (S) yr-1 1 Teragram (Tg) = 1012 grams Global sulfur dioxide (SO2) concentrations Marine Surface Layer [SO2] = 20 ppt Upper Troposphere (5km