[H-CG26] 農業残渣焼却のもたらす大気汚染と健康影響および解決への道筋

[HCG26-P06] Studies of chemical evolution of crop residue burning plume in northwest India based on sensor network observations: Secondary formation of PM_2.5 and loss of NO_x

*中山 智喜^1,2、松見 豊^3,2、Singh Tanbir^4,2、荒木 晶²、安富 奈津子²、Biswal Akash²、Mangaraj Poonam²、林田 佐智子²、梶野 瑞王^5,2、山地 一代^6,2、Patra Prabir^2,7 (1.長崎大学、2.総合地球環境学研究所、3.名古屋大学、4.SCVB Government College、5.気象研究所、6.神戸大学、7.海洋研究開発機構)

キーワード：微小粒子状物質 (PM2.5)、二次粒子生成、窒素酸化物 (NOx)、一酸化炭素 (CO)、小型センサ

Emissions of PM_2.5 (particle matter with aerodynamic diameters less than 2.5 micron) due to burning of crop residue such as rice stubble in Punjab and Haryana regions have recently been recognized to cause severe air pollution in northwest India during the post-monsoon season, especially, from October to November. During the crop residue burning (CRB), in addition to PM_2.5, a series of gaseous compounds including volatile organic compounds (VOCs) and nitrogen oxides (NO_x), are emitted and potentially contribute to secondary aerosol formation after aging processes in the atmosphere. In the Aakash project [1], network observation campaigns to monitor PM_2.5 and gaseous compounds including carbon monoxide (CO), NO_x, and ozone (O₃) were conducted using 32 instruments (named CUPI-Gs (compact and useful PM_2.5 instrument with gas sensors) [2]) in northwest India during CRB seasons in 2022 and 2023. In the 2022 campaign, two severe haze episodes with PM_2.5 concentrations above 400 μg/m³ have been observed from 2^nd to 3^rd and from 8^th to 11^th of November [3]. From backward trajectory analyses, the airmasses (plumes) influenced by CRB are considered to be transported from Punjab to Haryana and Delhi regions in the nighttime of 2^nd and 10^th November 2022, respectively. In this study, spatio-temporal variations of concentrations of PM_2.5 and gaseous compounds have been analyzed to examine transportation and aging processes for these plumes. Significant enhancement of PM_2.5 to ΔCO ratio were observed downwind regions, where Δ value represents enhancement over background concentration. Because PM_2.5/ΔCO ratio are expected to increase with secondary formation of PM_2.5, formation rates of secondary particles for these plumes have been estimated by fitting temporal evolutions of PM_2.5/ΔCO ratios. In addition, decrease in ΔNO_x to ΔCO ratio have been observed in downwind regions for these plumes. Using this ratio, oxidation processed of NO_x during transportation have also been examined.

[Acknowledgements]
This research is supported by Research Institute for Humanity and Nature (RIHN: a constituent member of NIHU) Project No. 14200133 (Aakash). We greatly thank to all participants of the network observations in Aakash project.

[Reference]
[1] Aakash project (https://aakash-rihn.org/). [2] Nakayama, T. and Matsumi, Y., Bunseki, 575, 492-497 (2022). [3] Singh, T., et al., Sci. Rep., 13, 13201 (2023).