Abstract. Formaldehyde (HCHO) in the ambient air not only causes cancer but is also an ideal
indicator of volatile organic compounds (VOCs), which are major precursors of
ozone (O3) and secondary organic aerosol (SOA) near the surface. It
is meaningful to differentiate between the direct emission and the secondary
formation of HCHO for HCHO pollution control and sensitivity studies of
O3 production. However, understanding of the sources of HCHO is
still poor in China, due to the scarcity of field measurements (both
spatially and temporally). In this study, tropospheric HCHO vertical column
densities (VCDs) in the Yangtze River Delta (YRD), East China, where HCHO
pollution is serious, were retrieved from the Ozone Mapping and Profiler
Suite (OMPS) onboard the Suomi National Polar-orbiting Partnership
(Suomi-NPP) satellite from 2014 to 2017; these retrievals showed good
agreement with the tropospheric HCHO columns measured using ground-based
high-resolution Fourier transform infrared spectrometry (FTS) with a
correlation coefficient (R) of 0.78. Based on these results, the cancer
risk was estimated both nationwide and in the YRD region. It was calculated
that at least 7840 people in the YRD region would develop cancer in their
lives due to outdoor HCHO exposure, which comprised 23.4 % of total
national cancer risk. Furthermore, the contributions of primary and secondary
sources were apportioned, in addition to primary and secondary tracers from
surface observations. Overall, the HCHO from secondary formation contributed
most to ambient HCHO and can be regarded as the indicator of VOC reactivity
in Hangzhou and in urban areas of Nanjing and Shanghai from 2015 to 2017, due
to the strong correlation between total HCHO and secondary HCHO. At
industrial sites in Nanjing, primary emissions more strongly influenced
ambient HCHO concentrations in 2015 and showed an obvious decreasing trend.
Seasonally, HCHO from secondary formation reached a maximum in summer and a
minimum in winter. In the spring, summer, and autumn, secondary formation had
a significant effect on the variation of ambient HCHO in urban regions of
Nanjing, Hangzhou, and Shanghai, whereas in the winter the contribution from
secondary formation became less significant. A more thorough understanding of
the variation of the primary and secondary contributions of ambient HCHO is
needed to develop a better knowledge regarding the role of HCHO in
atmospheric chemistry and to formulate effective control measures to decrease
HCHO pollution and the associated cancer risk.
Supplementary material to "Primary and secondary sources of
ambient
formaldehyde
in the
Yangtze River Delta based on OMPS observation"