Raman Microscopic Studies of the Physical and Chemical Properties of Particulate Matter in one of the World's Most Polluted Cities

Due to frequent wintertime temperature inversions and smoke emitted from individual stoves and coal-fired power plants to meet high heating demands during the sub-arctic winter, the annual average PM10 concentration in Ulaanbaatar, Mongolia is one of the highest in the world. With winter daily PM10 averages reaching as high as 4000 micrograms per cubic meter, the pollution has had devastating health effects for the 1.3 million living in Ulaanbaatar, with some studies estimating 25% of deaths in Ulaanbaatar are attributable to the high PM10 levels. At present, there is little information on particulate levels, the chemical and physical characteristics of the particles, or their ice-nucleating ability. Here we examine individual particles from Ulaanbaatar using optical and Raman microscopy. Particles are analyzed for size, shape, composition and mixing state. We also probe the ice nucleating ability of the particles using an environmental cell coupled to the microscope. Ice nucleation on the Ulaanbaatar particles is compared to ice nucleation on other solid particles such as mineral dust and volcanic ash. These studies aim to provide new insight into the chemical and physical properties of particulate matter in a highly polluted, yet understudied, city.