In this study, we investigated the chemical composition and
hygroscopicity of water-soluble fraction in PM2.5
collected from a rural site of Guanzhong Basin, a highly polluted region
in northwest China. Hygroscopic growth factors, g(RH), of water-soluble
matter(WSM) were measured by hygroscopic tandem differential mobility
analyzer(H-TDMA) with an initial dry particle diameter of 100 nm. The
g(90)WSM and κWSM was in the range of
1.08~1.49(1.35{plus minus}0.10) and
0.04~0.29(0.19{plus minus}0.06) in summer,
1.24~1.45(1.36{plus minus}0.07) and
0.12~0.26(0.20{plus minus}0.04) in winter,
respectively. We found that increased nitrate concentration at night in
summer suppressed 60-70% of the deliquescent point, and increased g(RH)
at elevated relative humidity, compared to daytime. Secondary inorganic
ions were the main components in heavy haze day, and greatly contributed
to the hygroscopicity of particles. In contrast, more potassium compound
and WSOM existed during Chinese Spring Festival event but exhibited no
deliquescence point in the process of hygroscopic growth with the
elevated RH. The g(90)WSOM and κWSOM,
obtained using ZSR model, were in the range of
1.06~1.52(1.25{plus minus}0.14) and
0.024~0.32(0.13{plus minus}0.09) in summer,
1.06~1.58(1.38{plus minus}0.15) and
0.02~0.38(0.22{plus minus}0.10) in winter,
respectively. The mean g(90)WSOM was in the range of
that of biomass burning aerosols, and a good correlation (R=0.71) was
found between g(90)WSOM and levoglucosan, confirming
that the aerosol’s hygroscopicity were highly influenced by biomass
burning in winter. Briefly, it is revealed that the aerosol in rural
regions of Guanzhong Basin is mainly influenced by biomass burning based
on the hygroscopicity in winter and summer.