Daily variations of size-segregated ambient particulate matter in Beijing

Daily, size-segregated particulate matter (PM) samples were collected at Peking University from March 2012 to April 2013. Seventeen indoor air samples were also collected over this period. Winter PM concentrations decreased compared with those reported a decade ago, but summer PM concentrations increased over the same time period. Increasing summer PM concentrations likely resulted from a shift in the major source of PM from primary coal burning to vehicle-associated secondary particle formation. A multiple regression model explained 62% of daily PM concentration variations, and wind direction was the most important factor controlling PM concentrations. Severe pollution was often associated with southeasterly winds, while westerly and northwesterly winds brought relatively clean air. Temperature, precipitation and relative humidity also affected PM concentrations. PM concentrations indoors were generally lower than, but significantly correlated with ambient concentrations. Indoor PM concentrations were also affected by wind speed and temperature. - Highlights: • Daily concentrations of five size fraction PMs were measured for a year. • The seasonality and source pattern were different from those reported a decade ago. • Severe pollution epidoses were associated with southeasterly winds. • Indoor PM concentrations were lower than but correlated with those in ambient air. - Size-segregated ambient PM concentrations in Beijing varied depending on wind direction; and PM concentrations indoors were well-correlated with, but lower than those outdoors