Fourier transform infrared time series of tropospheric HCN in eastern China: seasonality, interannual variability, and source attribution
Authors: Sun Youwen , Liu Cheng , Zhang Lin , Palm Mathias , Notholt Justus , Yin Hao , Vigouroux Corinne , Lutsch Erik , Wang Wei , Shan Changong , Blumenstock Thomas , Nagahama Tomoo , Morino Isamu , Mahieu Emmanuel , Strong Kimberly , Langerock Bavo , De Mazière Martine , Hu Qihou , Zhang Huifang , Petri Christof , Liu Jianguo 
Published: May 2020

Abstract. We analyzed seasonality and interannual variability of tropospheric hydrogen cyanide (HCN)
columns in densely populated eastern China for the first time. The results
were derived from solar absorption spectra recorded with a ground-based high-spectral-resolution Fourier transform infrared (FTIR) spectrometer in Hefei
(31∘54′ N, 117∘10′ E) between 2015 and
2018. The tropospheric HCN columns over Hefei, China, showed significant
seasonal variations with three monthly mean peaks throughout the year. The
magnitude of the tropospheric HCN column peaked in May, September, and December. The tropospheric HCN column reached a maximum monthly
mean of (9.8±0.78)×1015 molecules cm−2 in May
and a minimum monthly mean of (7.16±0.75)×1015 molecules cm−2 in November. In most cases, the tropospheric HCN columns
in Hefei (32∘ N) are higher than the FTIR observations in Ny-Ålesund (79∘ N), Kiruna (68∘ N), Bremen (53∘ N), Jungfraujoch (47∘ N), Toronto (44∘ N), Rikubetsu
(43∘ N), Izana (28∘ N), Mauna Loa (20∘ N), La
Reunion Maido (21∘ S), Lauder (45∘ S), and Arrival
Heights (78∘ S) that are affiliated with the Network for Detection
of Atmospheric Composition Change (NDACC). Enhancements of tropospheric HCN
column were observed between September 2015 and July 2016 compared to the
same period of measurements in other years. The magnitude of the enhancement
ranges from 5 % to 46 % with an average of 22 %. Enhancement of
tropospheric HCN (ΔHCN) is correlated with the concurrent
enhancement of tropospheric CO (ΔCO), indicating that enhancements
of tropospheric CO and HCN were due to the same sources. The GEOS-Chem tagged CO simulation, the global fire maps, and the potential source
contribution function (PSCF) values calculated using back trajectories
revealed that the seasonal maxima in May are largely due to the influence of
biomass burning in Southeast Asia (SEAS) (41±13.1 %), Europe
and boreal Asia (EUBA) (21±9.3 %), and Africa (AF) (22±4.7 %). The seasonal maxima in September are largely due to the influence
of biomass burnings in EUBA (38±11.3 %), AF (26±6.7 %),
SEAS (14±3.3 %), and North America (NA) (13.8±8.4 %).
For the seasonal maxima in December, dominant contributions are from AF (36±7.1 %), EUBA (21±5.2 %), and NA (18.7±5.2 %). The tropospheric HCN enhancement between September 2015 and July
2016 at Hefei (32∘ N) was attributed to an elevated influence of
biomass burnings in SEAS, EUBA, and Oceania (OCE) in this period. In
particular, an elevated number of fires in OCE in the second half of 2015
dominated the tropospheric HCN enhancement between September and December 2015. An
elevated number of fires in SEAS in the first half of 2016 dominated the
tropospheric HCN enhancement between January and July 2016.