Abstract. Vertical distributions of dicarboxylic acids, oxoacids, α-dicarbonyls and other organic tracer compounds in fine aerosols
(PM2.5) were investigated at three heights (8, 120 and
260 m) based on a 325 m meteorological tower in urban
Beijing in the summer of 2015. Results showed that the concentrations
of oxalic acid (C2), the predominant diacid, were more
abundant at 120 m (210±154 ng m−3) and
260 m (220±140 ng m−3) than those at the
ground surface (160±90 ng m−3). Concentrations of
phthalic acid (Ph) decreased with the increase in height, indicating
that local vehicular exhausts were the main contributor. Positive
correlations were noteworthy for C2 ∕ total diacids with mass
ratios of C2 to main oxoacids (Pyr and ωC2) and α-dicarbonyls (Gly and MeGly) in polluted
days (0.42≤r2≤0.65), especially at the ground
level. In clean days, the ratios of carbon content in oxalic acid to
water-soluble organic carbon (C2−C ∕ WSOC) showed larger
values at 120 and 260 m than those at the ground
surface. However, in polluted days, the C2−C ∕ WSOC ratio
mainly reached its maximum at ground level. These phenomena may
indicate the enhanced contribution of aqueous-phase oxidation to
oxalic acid in polluted days. Combined with the influence of wind
field, total diacids, oxoacids and α-dicarbonyls decreased by
22 %–58 % under the control on anthropogenic activities during
the 2015 Victory Parade period. Furthermore, the positive matrix
factorisation (PMF) results showed
that the secondary formation routes (secondary sulfate formation and
secondary nitrate formation) were the dominant contributors
(37 %–44 %) to organic acids, followed by biomass burning
(25 %–30 %) and motor vehicles (18 %–24 %). In this
study, the organic acids at ground level were largely associated
with local traffic emissions, while the long-range atmospheric
transport followed by photochemical ageing contributed more to diacids
and related compounds in the urban boundary layer than the ground
surface in Beijing.
Supplementary material to "Vertical distribution of particle-phase dicarboxylic acids, oxoacids and α-dicarbonyls in the urban boundary layer based on the 325-meter tower in Beijing"
