Bossolasco Adriana, Fernandez Rafael P, Li Qinyi, Mahajan Anoop S, Villamayor Julián, Barrera Javier A, Heard Dwayne E, Cuevas Carlos A, Caram Cyril, Szopa Sophie, Saiz-Lopez Alfonso
Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Blas Cabrera, CSIC Madrid Spain
Physics Institute of Northwest Argentina, National Research Council (INFINOA-CONICET), National University of Tucumán (UNT) Tucumán Argentina.
Environ Sci Atmos. 2025 Feb 19;5(5):547-562. doi: 10.1039/d4ea00141a. eCollection 2025 May 15.
Atmospheric oxidation largely determines the abundance and lifetime of short-lived climate forcers like methane, ozone and aerosols, as well as the removal of pollutants from the atmosphere. Hydroxyl, nitrate and chlorine radicals (OH, NO and Cl), together with ozone (O), are the main atmospheric oxidants. Short-lived halogens (SLH) affect the concentrations of these oxidants, either through direct chemical reactions or indirectly by perturbing their main sources and sinks. However, the effect of SLH on the combined abundance of global oxidants during historical periods remains unquantified and is not accounted for in air quality and climate models. Here, we employ a state-of-the-art chemistry-climate model to comprehensively assess the role of SLH on atmospheric oxidation under both pre-industrial (PI) and present-day (PD) conditions. Our results show a substantial reduction in present-day atmospheric oxidation caused by the SLH-driven combined reduction in the global boundary layer levels of OH (16%), NO (38%) and ozone (26%), which is not compensated by the pronounced increase in Cl (2632%). These global differences in atmospheric oxidants show large spatial heterogeneity due to the variability in SLH emissions and their nonlinear chemical interactions with anthropogenic pollution. Remarkably, we find that the effect of SLH was more pronounced in the pristine PI atmosphere, where a quarter (OH: -25%) and half (NO: -49%) of the boundary layer concentration of the main daytime and nighttime atmospheric oxidants, respectively, were controlled by SLH chemistry. The lack of inclusion of the substantial SLH-mediated reduction in global atmospheric oxidation in models may lead to significant errors in calculations of atmospheric oxidation capacity, and the concentrations and trends of short-lived climate forcers and pollutants, both historically and at present.
大气氧化在很大程度上决定了甲烷、臭氧和气溶胶等短期气候强迫因子的丰度和寿命，以及大气中污染物的清除。羟基、硝酸根和氯自由基（OH、NO和Cl），以及臭氧（O）是主要的大气氧化剂。短寿命卤素（SLH）通过直接化学反应或间接扰动其主要源和汇来影响这些氧化剂的浓度。然而，历史时期SLH对全球氧化剂综合丰度的影响仍未得到量化，空气质量和气候模型中也未考虑这一因素。在此，我们采用先进的化学气候模型，全面评估SLH在工业化前（PI）和现代（PD）条件下对大气氧化的作用。我们的结果表明，由于SLH驱动全球边界层中OH（下降16%）、NO（下降38%）和臭氧（下降26%）的浓度综合降低，导致现代大气氧化大幅减少，而Cl浓度显著增加（增加2632%）并不能弥补这一减少。由于SLH排放的变异性及其与人为污染的非线性化学相互作用，这些全球大气氧化剂差异呈现出很大的空间异质性。值得注意的是，我们发现SLH在原始的PI大气中的影响更为显著，其中主要白天和夜间大气氧化剂边界层浓度的四分之一（OH：下降25%）和一半（NO：下降49%）分别受SLH化学过程控制。模型中未考虑SLH介导的全球大气氧化大幅减少，可能会导致在计算大气氧化能力以及历史和当前短期气候强迫因子和污染物的浓度及趋势时出现重大误差。
