Direct observations of organic aerosols in common wintertime hazes in North China: Insights into direct emissions from Chinese residential stoves.

Citation:

Chen SR, Xu L, Zhang YX, Chen B, Wang XF, Zhang XY, Zheng M*, Chen JM, Wang WX, Sun YL, et al. Direct observations of organic aerosols in common wintertime hazes in North China: Insights into direct emissions from Chinese residential stoves. Atmos. Chem. Phys. 2017;17:1259-1270.

摘要:

Many studies have focused on the physicochemical properties of aerosol particles in unusually severe haze
episodes in North China instead of the more frequent and less
severe hazes. Consistent with this lack of attention, the morphology and mixing state of organic matter (OM) particles in
the frequent light and moderate (L & M) hazes in winter in
the North China Plain (NCP) have not been examined, even
though OM dominates these fine particles. In the present
work, morphology, mixing state, and size of organic aerosols
in the L & M hazes were systematically characterized using transmission electron microscopy coupled with energydispersive X-ray spectroscopy, atomic force microscopy, and
nanoscale secondary ion mass spectrometer, with the comparisons among an urban site (Jinan, S1), a mountain site
(Mt. Tai, S2), and a background island site (Changdao, S3)
in the same hazes. Based on their morphologies, the OM particles were divided into six different types: spherical (type 1),
near-spherical (type 2), irregular (type 3), domelike (type 4),
dispersed-OM (type 5), and OM-coating (type 6). In the three
sampling sites, types 1–3 of OM particles were most abundant in the L & M hazes and most of them were internally
mixed with non-OM particles. The abundant near-spherical
OM particles with higher sphericity and lower aspect ratio
indicate that these primary OM particles formed in the cooling process after polluted plumes were emitted from coal
combustion and biomass burning. Based on the Si-O-C ratio in OM particles, we estimated that 71 % of type 1–3 OM
particles were associated with coal combustion. Our result
suggests that coal combustion in residential stoves was a
widespread source from urban to rural areas in NCP. Average
OM thickness which correlates with the age of the air masses
in type 6 particles only slightly increased from S1 to S2 to S3,
suggesting that the L & M hazes were usually dry (relative
humidity < 60 %) with weak photochemistry and heterogeneous reactions between particles and gases. We conclude
that the direct emissions from these coal stoves without any
pollution controls in rural areas and in urban outskirts contribute large amounts of primary OM particles to the regional
L & M hazes in North China.