GAW Report No. 205 - IGAC Project

CHAPTER 5 - NORTH AMERICACoordinating Authors: David Parrish (1)Contributing Authors: Hanwant Singh (2) , Luisa Molina (3)(4) , Sasha Madronich (5)(1)NOAA, ESRL, Chemical Sciences Division, Boulder, CO, USA(2)NASA, Ames Research Center, Field, CA, USA(3)Molina Center for Strategic Studies in Energy and the Environment (MCE2, La Jolla, CA, USA(4)Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA USA(5)National Center for Atmospheric Research, Atmospheric Chemistry Division and Chemical Processingand Regional Modelling Group, Boulder, CO, USANorth American megacities include Mexico City, perhaps the second largest metropolitanarea in the world, and Los Angeles and New York City in the United States, two of the ten largestmetropolitan areas. Figure 1 shows the population density of North America. The megacities ofLos Angeles, New York, and Mexico City are visible, as well as several other high-density urbanareas such as Houston, Texas. Summertime photochemical smog was first recognized as asevere environmental problem in Los Angeles, and has been the subject of extensive studies theresince the 1940’s [e.g., Haagen-Smit, 1952]. Differences in topography, meteorological conditions,and anthropogenic emissions lead to marked differences in the air quality considerations in theseNorth American megacities as well as their impacts on the larger troposphere. Figure 2 showsemissions of CO, NO X , and SO 2 for the year 2000 throughout North America. Probably thegreatest difference in emissions between the megacities in North America is their SO 2 emissions,which depend greatly on the type of coal (low- versus high-sulphur) used in energy production.This chapter discusses these differences, as well as the similarities. The greater Houston, Texasurban area in the United States is discussed as an additional contrast; with a populationapproaching 6 million, this area is not generally considered a megacity, but it is a large urbancentre of particular interest since it is home to a large fraction of the petrochemical industrialfacilities of the US, which leads to a unique mix of anthropogenic emissions.Figure 1 - Map of the population density in North America (persons per km 2 ), based on 0.25 o gridded data for 2000from the Center for International Earth Science Information Network (CIESIN) at Columbia University[http://sedac.ciesin.columbia.edu/gpw/]172