资源环境科技发展态势分析平台

Overall, the average concentration of nonrefractory submicron aerosol (NR-PM₁) + BC was 35.1 μg m⁻³, which was composed of 38 % organics, 12 % SO₄, 30 % NO₃, 13 % NH₄ and 5 % BC. The organics had an average oxygen-to-carbon (O / C) ratio of 0.52 and an average organic mass-to-carbon (OM / OC) ratio of 1.86. Seven distinct sources of organic aerosols (OA) were identified via positive matrix factorization (PMF) analysis of the HR-AMS data: vehicle-emitted hydrocarbon-like OA (HOA), cooking OA (COA), solid fuel burning-emitted OA (SFOA) and 4 different types of oxidized secondary OA with varying oxidation degrees and temporal trends.

Of the 40 days of the measurement period, 23 were identified as haze days (daily average: > 35 μg m⁻³), during which three severe haze episodes were recorded. In particular, PM₁ concentration exceeded 100 μg m³ during the first episode when an alert was issued and strict emission controls were implemented in the SMA. Our results showed that nitrate dominated during the three haze episodes and accounted for 39–43 % of the PM₁ concentration on average (vs. 21–24 % during the low-loading period), for which there were indications of regional transport influences. Two regional transport-influenced OOA, i.e., less oxidized OOA2 (LO-OOA2) and more oxidized OOA2 (MO-OOA2), contributed substantially to the total PM₁ during the haze period (12–14 % vs. 7 % during the low-loading period), as well. In contrast, HOA and COA only contributed little (4–8 % vs. 4–6 % during the low-loading period) to the PM₁ concentration during the haze days, indicating that local emissions were likely not the main reason for the severe haze issues. Hence, from simultaneous downwind (SMA) and upwind (Beijing) measurements using AMS and ACSM (aerosol chemical speciation monitor) over the same period, the temporal variations in PM₁ and each chemical species showed peak values on the order of Beijing (upwind)) to the SMA for approximately two days. Furthermore, lead (Pb) derived from HR-AMS measurements was observed to increase significantly during the haze period and showed good correlations with MO-OOA2 and LO-OOA2, consistent with regional sources. Multiple linear regression model indicated that the transported regionally processed air masses contributed significantly to Pb in the SMA (31 %), especially during the haze period although the local burning also important by contributing 38 %. The above results suggest that regional transport of polluted air masses might have played an important role in the formation of the haze episodes in the SMA during early spring.