person's mobility, awareness, or behavior. Researchers have noted that individuals with cognitive health issues (e.g. depression, dementia, Parkinson's disease) are more at risk when faced with high temperatures and "need to take extra care" as cognitive performance has been shown to be differentially affected by heat. People with diabetes, are overweight, have sleep deprivation, or have cardiovascular/cerebrovascular conditions should avoid too much heat exposure. Some common medications that have an effect on thermoregulation can also increase the risk of mortality. Specific examples include anticholinergics, diuretics, phenothiazines and barbiturates. Not only health, but heat can also affect behavior. A U.S. study suggests that heat can make people more irritable and aggressive, noting that violent crimes increased by 4.58 out of 100,000 for every one degree increase in temperature. A researcher found that high UHI intensity correlates with increased concentrations of air pollutants that gathered at night, which can affect the next day's air quality. These pollutants include volatile organic compounds, carbon monoxide, nitrogen oxides, and particulate matter. The production of these pollutants combined with the higher temperatures in UHIs can quicken the production of ozone. Ozone at surface level is considered to be a harmful pollutant. Studies suggest that increased temperatures in UHIs can increase polluted days but also note that other factors (e.g. air pressure, cloud cover, wind speed) can also have an effect on pollution. Studies from Hong Kong have found that areas of the city with poorer outdoor urban air ventilation tended to have stronger urban heat island effects and had significantly higher all-cause mortality compared to areas with better ventilation. The Centers for Disease Control and Prevention notes that it "is difficult to make valid projections of heat-related illness and death under varying climate change scenarios" and that "heat–related deaths are preventable, as evidenced by the decline of all-cause mortality during heat events over the past 35 years". However, some studies suggest that the effects of UHIs on health may be disproportionate, since the impacts may be unevenly distributed based on a variety of factors such as age, ethnicity and socioeconomic status. This raises the possibility of health impacts from UHIs being an environmental justice issue. Inequality of tree canopy cover Relationship between neighborhood income and tree canopy cover In recent years, researchers have discovered a strong correlation between neighborhood income and tree canopy cover. In 2010, researchers at Auburn University and University of Southern California found