that have higher air pollution also have a greater chance of having a higher population density, higher crime rates and lower income levels, all of which can lead to higher infant mortality rates. The key pollutant for infant mortality rates is carbon monoxide. Carbon monoxide is a colorless, odorless gas that does great harm especially to infants because of their immature respiratory system. Another major pollutant is second-hand smoke, which is a pollutant that can have detrimental effects on a fetus. According to the American Journal of Public Health, "in 2006, more than 42 000 Americans died of second hand smoke-attributable diseases, including more than 41 000 adults and nearly 900 infants ... fully 36% of the infants who died of low birth weight caused by exposure to maternal smoking in utero were Blacks, as were 28% of those dying of respiratory distress syndrome, 25% dying of other respiratory conditions, and 24% dying of sudden infant death syndrome." The American Journal of Epidemiology also stated that "Compared with nonsmoking women having their first birth, women who smoked less than one pack of cigarettes per day had a 25% greater risk of mortality, and those who smoked one or more packs per day had a 56% greater risk. Among women having their second or higher birth, smokers experienced 30% greater mortality than nonsmokers." Modern research in the United States on racial disparities in infant mortality suggests a link between the institutionalized racism that pervades the environment and high rates of African American infant mortality. In synthesis of this research, it has been observed that "African American infant mortality remains elevated due to the social arrangements that exist between groups and the lifelong experiences responding to the resultant power dynamics of these arrangements." It is important to note that infant mortality rates do not decline among African Americans even if their socio-economic status does improve. Parker Dominguez at the University of Southern California has made some headway in determining the reasoning behind this, claiming black women are more prone to psychological stress than other women of different races in the United States. Stress is a lead factor in inducing labor in pregnant women, and therefore high levels of stress during pregnancy could lead to premature births that have the potential to be fatal for the infant. Early childhood trauma Early childhood trauma includes physical, sexual, and psychological abuse of a child ages