Spatial-temporal variability of PM air quality in Beijing, China during 2013-2018.

This study investigates spatial-temporal variability and trends of ambient PM in Beijing, China, using data collected from eight urban and four suburban stations. During 2013-2018, the city-wide annual PM concentrations decreased significantly by 40% (84 μg/m in 2013 vs. 50 μg/m in 2018). The decreasing PM trend is more pronounced in winter and during the heating season (November-March), in urban areas, and at the median and upper percentiles of PM concentrations. The 95th percentile PM concentrations had decreased by 20 μg/m/yr in the heating season and 16 μg/m/yr in the non-heating season. During the six-year study period, there was a significant increase in excellent air quality days (PM concentration < 35 μg/m) and a significant decrease in heavy pollution days (PM concentration > 150 μg/m). PM concentrations were strongly correlated across the 12 stations. Urban areas in south Beijing experienced higher PM levels than suburban sites at every hour-of-day, day-of-week, and month-of-year. PM levels were higher during winter and the heating season, when PM emission was high due to space heating and mixing layer heights were low. PM was higher at weekends than during weekdays, when 20% of private passenger vehicles are prohibited, and higher at night than during the day, when heavy duty delivery vehicles are not permitted. These temporal and spatial trends suggest that Beijing's PM is strongly impacted by local emissions. Our results indicate, control strategies implemented were successful in Beijing's air quality improvement, but further reduction of PM concentrations in Beijing could be challenging due to significant contribution from its neighboring cities, calling for comprehensive and collaborative efforts in regional/national scale.