Air pollution is today recognized as an important global risk factor for disease. Decades of research and a number of long-term exposure to air pollution studies have demonstrated that people who live in more polluted areas develop more often chronic and infectious disease and die prematurely as compared to people living in areas with low air pollution. In this lecture, I will describe the global levels and trends in major air pollutants and related health burden. As you have seen, there are substantial differences in the air pollution levels around the world. In 2015, the highest levels of PM 2.5 were seen in South and Southeast Asia, China, and Central and Western sub-Saharan Africa. Nearly all, 86% of the most extreme concentrations above 75 micrograms per cubic meter, were experienced by populations in China, India, Pakistan, and Bangladesh due to combustion emissions from household solid fuel used for cooking and heating, coal-fired power plants, agricultural and other open burning, and industrial transportation-related sources. Some of the highest levels of PM 2.5 are also seen in North Africa, and the Middle East, especially Saudi Arabia and Egypt, due to high levels of wind-blown dust. PM 2.5 levels were lowest, below eight micrograms per cubic meter, in Brunei, Sweden, Greenland, New Zealand, Australia, Finland, Canada and several Pacific and Caribbean island nations. In 2015, 92% of the world's population lived in areas that exceeded the World Health Organization's 10 micrograms per cubic meter guideline for PM 2.5, and 50% above WHO interim target three of 35 micrograms per cubic meter. Global population weighted PM 2.5 levels increased by 11% between 1990 and 2015, with the largest increase since 2010. The figure illustrates trends in population-weighted PM 2.5 levels for the 10 most populated countries in the world and European Union between 1990 and 2015. Bangladesh, India and China had the highest levels and experienced the sharpest increase in PM 2.5 levels. PM 2.5 levels decreased sharply in Nigeria, possibly due decline in mineral dust emissions and open burning. PM 2.5 levels in Russia, the European Union, Brazil, and United States declined slightly since 1990, and were stable in Indonesia and Japan. These trends show increasing disparities between the countries. Less polluted locations have become cleaner, and most polluted countries more polluted, with a 10-fold range among these countries. Ozone is a gas that was associated with respiratory diseases independent of PM 2.5. Ozone concentrations are calculated as averages during the warm season, when ozone levels are highest. Ozone concentrations are less variable than PM 2.5, and were relatively high in the United States, China, and some countries of western and central sub-Saharan Africa, the Middle East, and South Asia. Ozone levels increased by 7% globally between 1990 and 2015. The burden of disease from air pollution is measured in two ways, first, in the number of deaths that can be attributed to air pollution, and secondly, in Disability Adjusted Life Years, or so-called DALYs that can be attributed to air pollution. DALYs are the years of life lost due to dying earlier than expected plus the years lived with disability. Attributing deaths and DALYs to air pollution requires estimates of population-weighted exposure to air pollution, estimates of relative risks across the exposure distribution, and estimates of deaths and DALYs for disease causally linked to air pollution. In 2015, the analysis of the Global Burden of Diseases, Injuries, and Risk Factors Study estimated the burden of disease attributable to 79 risk factors in 195 countries. Exposure to PM 2.5 ranked as the fifth highest ranking risk factor for death after high blood pressure and smoking. Air pollution ranked higher than high body mass index, alcohol use, and low physical activity. Exposure to PM 2.5 was responsible for 4.2 million deaths, representing 7.6% of total global deaths. Furthermore, exposure to PM 2.5 contributed to 103 million DALYs representing 4.3% of global DALYs. Exposure to ozone was responsible for additional 254,000 deaths and loss of 4.1 million DALYs from chronic pulmonary disease in 2015. So which diseases are people dying from due to air pollution? Most of the deaths and DALYs, about 60%, attributable to PM 2.5, were due to ischemic heart and cerebral vascular diseases, followed by Chronic Obstructive Pulmonary Disease, or COPD, lower respiratory infections, and lung cancer. Number of deaths attributed to PM 2.5 in 2015 varied substantially between the countries. The majority, 59% of the 4.2 million global deaths attributable to PM 2.5, occurred in South and East Asia. Age-standardized mortality rates decreased from 66 per 100,000 people in 1990 to 57 per 100,000 people in 2015 mainly due to improved air quality and declining mortality rates due to cardiovascular diseases in high-income countries. However, the global mortality due to ambient PM 2.5 increased from 3.5 million in 1990 to 4.2 million in 2015 due to aging populations, population growth, and increasing air pollution levels in low and middle income countries such as China and India. In conclusion, outdoor air pollution contributes substantially to the global burden of disease which has increased in the past 25 years. It is important to note that the real burden is probably underestimated as the 2015 study did not include preterm birth, asthma, type two diabetes, and dementia which have been associated with PM 2.5 in last several years. Thank you for watching.