Global health risk studies (by the world Health Organization) compiled many other health impact studies. It was easiest for them to analyze and correlate particulate matter (10 micron and 2.5 micron)

http://nextbigfuture.com/2011/03/global-health-risks.html

http://www.who.int/healthinfo/global_burden_disease/GlobalHe...

In the year 2004, outdoor air pollution in urban areas was responsible for almost 1.2 million deaths (2% of all deaths) and 0.6% of the global burden of disease

Exposure to particulate matter, including metals, has been linked to a range of adverse health outcomes, including modest transient changes in the respiratory tract and impaired pulmonary function, increased risk of symptoms requiring emergency room or hospital treatment, and increased risk of death from cardiovascular and respiratory diseases or lung cancer. Particulate matter is estimated to cause about 8% of deaths from lung cancer, 5% of deaths from cardiopulmonary disease and about 3% of deaths from respiratory infections.

The impact of outdoor air pollution on the burden of disease in the world’s cities is large, but an assessment of sources of uncertainty, including the fact that only mortality impacts of exposure to PM were estimated, suggests that the impact is actually underestimated.

The coal pollution deaths are increased heart attacks and lung disease and more hospitalization from asthma and other illnesses.

Because coal pollution isn't listed as a cause of death (just like all pollution). It raises the incidence of many other diseases, and those diseases are listed as the cause of death. Coal also has additional direct deaths in e.g., mining accidents.

The numbers are nice round numbers because, well, there are somewhat imprecise. Looking up actual studies that came up with them would give methodology & margins of error.

Compare to, for example, smoking. The cause of death will be e.g., lung cancer. But had he not smoked for 30 years, he probably would have lived longer.