Abstract. To comprehensively evaluate the effects of the recent “2+26” regional
strategy for air quality improvement, we compared the variations in
PM2.5 concentrations in Beijing during four pollution episodes with
different emission-reduction strategies. The 2+26 strategy implemented
in March 2018 led to a mean PM2.5 concentration 16.43 % lower than
that during the pollution episode in March 2013, when no specific
emission-reduction measures were in place. The same 2+26 strategy
implemented in November 2017 led to a mean PM2.5 concentration 32.70 % lower than that during the pollution episode in November 2016,
when local emission-reduction measures were implemented. The results
suggested that the effects of the 2+26 regional emission-reduction
measures on PM2.5 reductions were influenced by a diversity of factors
and could differ significantly during specific pollution episodes.
Furthermore, we found the proportions of sulfate ions decreased
significantly, and nitrate ions were the dominant PM2.5 components
during the two 2+26 orange alert periods. Meanwhile, the relative
contribution of coal combustion to PM2.5 concentrations in Beijing
during the pollution episodes in March 2013, November 2016, November 2017
and March 2018 was 40 %, 34 %, 28 % and 11 %, respectively,
indicating that the recent “Coal to Gas” project and the contingent
2+26 strategy led to a dramatic decrease in coal combustion in the
Beijing–Tianjin–Hebei region. On the other hand, the relative contribution
of vehicle exhaust during the 2+26 orange alert periods in
November 2017 and March 2018 reached 40 % and 54 %, respectively. The relative
contribution of local emissions to PM2.5 concentrations in Beijing also
varied significantly and ranged from 49.46 % to 89.35 % during the four
pollution episodes. These results suggested that the 2+26 regional
emission-reduction strategy should be implemented with red air pollution
alerts during heavy pollution episodes to intentionally reduce the dominant
contribution of vehicle exhausts to PM2.5 concentrations in Beijing,
while specific emission-reduction measures should be implemented accordingly
for different cities within the 2+26 framework.
Evaluating the “2+26” regional strategy for air quality improvement during two air pollution alerts in Beijing: variations in PM<sub>2.5</sub> concentrations, source apportionment, and the relative contribution of local emission and regional transport
