Fourier transform infrared time series of tropospheric HCN in eastern China: seasonality, interannual variability, and source attribution

Youwen Sun,Cheng Liu,Thomas Blumenstock,Erik Lutsch,Kimberly Strong,Tomoo Nagahama,Bavo Langerock,Corinne Vigouroux,Justus Notholt,Huifang Zhang,Emmanuel Mahieu,Isamu Morino,Lin Zhang,Qihou Hu,Hao Yin,Christof Petri,Changong Shan,Martine De Mazière,Wei Wang,Jianguo Liu,Mathias Palm

doi:10.5194/acp-20-5437-2020

Abstract

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.

Highlights

Atmospheric hydrogen cyanide (HCN) is an extremely hazardous gas that threatens human health and terrestrial ecosystems (Andreae and Merlet, 2001; Akagi et al, 2011; Rinsland et al, 2002)
Enhancements of tropospheric HCN column were observed between September 2015 and July 2016 compared to the same period of measurements in other years
Sun et al.: Fourier transform infrared (FTIR) time series of tropospheric HCN in eastern China ( HCN) is correlated with the concurrent enhancement of tropospheric CO ( CO), indicating that enhancements of tropospheric CO and HCN were due to the same sources

Summary

Introduction

Atmospheric hydrogen cyanide (HCN) is an extremely hazardous gas that threatens human health and terrestrial ecosystems (Andreae and Merlet, 2001; Akagi et al, 2011; Rinsland et al, 2002). The principle pathway for an HCN sink is ocean uptake, which accounts for 0.73 to 1.0 Tg N yr−1 (Li et al, 2009). Li et al (2003, 2009), Lupu et al (2009), Vigouroux et al (2012), and Zeng et al (2012) showed that the observed variability of HCN can be reproduced by the chemical model simulations where biomass burning and ocean uptake provide the main source and sink, respectively (Li et al, 2009, 2003; Lupu et al, 2009; Vigouroux et al, 2012; Zeng et al, 2012) The lifetime of HCN is 2–5 months in the troposphere and several years in the stratosphere. Li et al (2003, 2009), Lupu et al (2009), Vigouroux et al (2012), and Zeng et al (2012) showed that the observed variability of HCN can be reproduced by the chemical model simulations where biomass burning and ocean uptake provide the main source and sink, respectively (Li et al, 2009, 2003; Lupu et al, 2009; Vigouroux et al, 2012; Zeng et al, 2012)

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