pollution underneath, and turning it into the most infamously smog-plagued city of Latin America. Within one generation, the city has changed from being known for some of the cleanest air of the world into one with some of the worst pollution, with pollutants like nitrogen dioxide being double or even triple international standards. Santiago, Chile Similar to Mexico City, the air pollution of Santiago valley, located between the Andes and the Chilean Coast Range, turn it into the most infamously smog-plagued city of South America. Other aggravates of the situation reside in its high latitude (31 degrees South) and dry weather during most of the year. Tehran, Iran In December 2005, schools and public offices had to close in Tehran and 1600 people were taken to hospital, in a severe smog blamed largely on unfiltered car exhaust. United States Smog was brought to the attention of the general U.S. public in 1933 with the publication of the book "Stop That Smoke", by Henry Obermeyer, a New York public utility official, in which he pointed out the effect on human life and even the destruction of of a farmer's spinach crop. Since then, the United States Environmental Protection Agency has designated over 300 U.S. counties to be non-attainment areas for one or more pollutants tracked as part of the National Ambient Air Quality Standards. These areas are largely clustered around large metropolitan areas, with the largest contiguous non-attainment zones in California and the Northeast. Various U.S. and Canadian government agencies collaborate to produce real-time air quality maps and forecasts. To combat smog conditions, localities may declare "smog alert" days, such as in the Spare the Air program in the San Francisco Bay Area. By 1970, Congress enacted the Clean Air Act to regulate air pollutant emissions. In the United States, smog pollution kills 24,000 Americans every year. The U.S. is among the dirtier countries in terms of smog, ranked 123 out of 195 countries measured, where 1 is cleanest and 195 is most smog polluted. Los Angeles and the San Joaquin Valley Because of their locations in low basins surrounded by mountains, Los Angeles and the San Joaquin Valley are notorious for their smog. Heavy automobile traffic, combined with the additional effects of the San Francisco Bay and Los Angeles/Long Beach port complexes, frequently contribute to further air pollution. Los Angeles, in particular, is strongly predisposed to the accumulation of smog,