The variability of biomass burning and its influence on regional aerosol properties during the wheat harvest season in North China

• The spatial–temporal variation of wheat straw burning in June in North China from 2005 to 2012 was explored.
• The fire occurrences exhibit oscillatory changes with a peak and explosive growth in 2012.
• Intensive regional haze was caused by both fire and urban/industrial emissions under high humidity and south winds.
• The formation of secondary inorganic particles was intensified under smoke plumes and urban/industrial pollutants in Beijing.

The spatial–temporal variation of biomass burning in June during the wheat harvest season in the North China (32–41°N, 111–120°E) and its influence on the regional aerosol optical depth (AOD) and the chemical compositions of size-segregated aerosols in the urban environment were investigated to evaluate the effectiveness of the burn ban policy and the influence on regional pollution. Fire events that occurred in early and middle June accounted for approximately 89% of the events during the month, and fire points located in mid-eastern China (32.5–35.5°N, 114–120°E) comprised 71%. The occurrences exhibit oscillatory changes with a minimum in 2008 (during the Beijing Olympics) and a peak and explosive growth in 2012. Under high relative humidity and south winds, fire emissions from straw burning combined with high urban/industrial emissions to produce intensive regional haze pollution in the North Plain. The formation of secondary inorganic particles was intensified due to the interactions of smoke plumes and urban/industrial pollutants in an urban environment. Higher concentrations and percentages (79%) of sulfate, nitrate, ammonium, and organic carbon in the fine particles under high relative humidity conditions contributed to a deteriorated urban visibility. Therefore, stronger management and a comprehensive ban on wheat straw burning in June are urgently needed, especially during years when the south wind is dominant.