Drivers of the rapid rise and daily-based accumulation in PM₁

Submicron particle matter (PM₁) that rapidly reaches exceedingly high levels in several or more hours in the North China Plain (NCP) has been threating~400 million individuals' health for decades. The precise cause of the rapid rise in PM₁ remains uncertain. Based on sophisticated measurements in PM₁ characterizations and corresponding boundary-layer (BL) meteorology in the NCP, it demonstrates that this rising is mainly driven by BL meteorological variability. Large increases in near-ground inversions and decreases in vertical heat/momentum fluxes during the day-night transition result in a significant reduction in mixing space. The PM₁ that is vertically distributed before accumulates at the near-ground and then experiences a rapid rise. Besides meteorological variability, a part of the rise in organics is ascribed to an increase of coal combustion at midnight. The daily-based accumulation of PM₁ is attributed to day-to-day vertical meteorological variability, particularly diminishing mixing layer height exacerbated by aerosol-radiation feedback. Resolved by a multiple linear regression model, BL meteorological variability can explain 71% variances of PM₁. In contrast, secondary chemical reactions facilitate the daily-based accumulation of PM₁ rather than the rapid rise. Our results show that BL meteorological variability plays a dominant role in PM₁ rising and day-to-day accumulation, which is crucial for understanding the mechanism of heavy pollution formation.