Mapping the drivers of formaldehyde (HCHO) variability from 2015 to 2019 over eastern China: insights from Fourier transform infrared observation and GEOS-Chem model simulation
2021
Abstract. The major air pollutant emissions have decreased, and the overall air quality has substantially improved across China in recent years as a consequence of
active clean air policies for mitigating severe air pollution problems. As
key precursors of formaldehyde (HCHO) and ozone (O 3 ), the volatile
organic compounds (VOCs) in China are still increasing due to the lack of
mitigation measures for VOCs. In this study, we investigated the drivers of
HCHO variability from 2015 to 2019 over Hefei, eastern China, by using ground-based high-resolution Fourier transform infrared (FTIR) spectroscopy
and GEOS-Chem model simulation. Seasonal and interannual variabilities of
HCHO over Hefei were analyzed and hydroxyl (OH) radical production rates from HCHO photolysis were evaluated. The relative contributions of emitted
and photochemical sources to the observed HCHO were analyzed by using ground-level carbon monoxide (CO) and O x (O 3 + nitrogen oxide
(NO 2 )) as tracers for emitted and photochemical HCHO, respectively.
Contributions of emission sources from various categories and geographical
regions to the observed HCHO summertime enhancements were determined by
using a series of GEOS-Chem sensitivity simulations. The column-averaged dry
air mole fractions of HCHO ( XHCHO ) reached a maximum monthly mean value
of 1.1 ± 0.27 ppbv in July and a minimum monthly mean value of 0.4 ± 0.11 ppbv in January. The XHCHO time series from 2015 to 2019
over Hefei showed a positive change rate of 2.38 ± 0.71 % per year.
The photochemical HCHO is the dominant source of atmospheric HCHO over Hefei
for most of the year (68.1 %). In the studied years, the HCHO photolysis
was an important source of OH radicals over Hefei during all sunlight hours of both summer and winter days. The oxidations of both methane (CH 4 )
and nonmethane VOCs (NMVOCs) dominate the HCHO production over Hefei and
constitute the main driver of its summertime enhancements. The NMVOC-related HCHO summertime enhancements were dominated by the emissions within
eastern China. The observed increasing change rate of HCHO from 2015 to 2019
over Hefei was attributed to the increase in photochemical HCHO resulting
from increasing change rates of both CH 4 and NMVOC oxidations, which overwhelmed the decrease in emitted HCHO. This study provides a valuable
evaluation of recent VOC emissions and regional photochemical capacity in China. In addition, understanding the sources of HCHO is a necessary step
for tackling air pollution in eastern China and mitigating the emissions of
pollutants.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
90
References
2
Citations
NaN
KQI