13 May 2019
13 May 2019
Status: this preprint was under review for the journal ACP but the revision was not accepted.

Is the photochemistry activity weak during haze events? – A novel exploration on the photoinduced heterogeneous reaction of NO2 on mineral dust

Tao Wang1, Yangyang Liu1, Yue Deng1, Hanyun Cheng1, Yang Yang1, Yiqing Feng1, Muhammad Ali Tahir1, Xiaozhong Fang1, Xu Dong1, Kejian Li1, Saira Ajmal1, Aziz-Ur-Rahim Bacha1, Iqra Nabi1, Hongbo Fu1, Liwu Zhang1,2, and Jianmin Chen1 Tao Wang et al.
  • 1Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science & Engineering, Fudan University, Shanghai, 200433, Peoples’ Republic of China
  • 2Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, Peoples’ Republic of China

Abstract. Despite the increased awareness of heterogeneous reaction on mineral dust, the knowledge of how the intensity of solar irradiation influences the photochemistry activity remains a crucially important part in atmospheric research. Relevant studies have not seriously discussed the photochemistry under weak sunlight during haze, and thus ignored some underlying pollution and toxicity. Here, we investigated the heterogeneous formation of nitrate and nitrite under various illumination conditions by laboratory experiments and field observations. Observed by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), water-solvated nitrate was the main surface product, followed by other species varying with illumination condition. The growth of nitrate formation rate tends to be slow after the initial fast with increasing light intensity. For example, the geometric uptake coefficient (γgeo) under 30.5 mW/cm2 (5.72 × 10−6) has exceeded the 50 % of that under 160 mW/cm2 (1.13 × 10−5). This case can be explained by the excess NO2 adsorption under weak illumination while the excess photoinduced active species under strong irradiation. Being negatively associated with nitrate (R2 = 0.748, P < 0.01), nitrite acts as the intermediate and decreases with increasing light intensity via oxidation pathways. Similar negative dependence appears in coarse particles collected during daytime (R2 = 0.834, P < 0.05), accompanied by the positive association during nighttime (R2 = 0.632, P < 0.05), suggesting illumination a substantial role in atmospheric nitrogen cycling. Overall, for the nitrate formation, the conspicuous response under slight illumination offers opportunities to explain the secondary aerosol burst during haze episodes with weak irradiation. Additionally, high nitrite levels accompanied by low nitrate concentrations may induce great health risk which was previously neglected. Further, Monte Carlo simulation coupled with sensitivity analysis may provide a new insight in the estimations of kinetics parameters for atmospheric modelling studies.

Tao Wang et al.

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Tao Wang et al.


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Short summary
We studied the heterogeneous formation of nitrate and nitrite aerosols by in-situ laboratory tests and field observations. Sunlight becomes the protagonist under weak illumination, while a costar under strong irradiation, attributing to the balance between NO2 adsorption and the formation of photoinduced active species. Meanwhile, sunlight determines the association between atmospheric nitrate and nitrite. We hope this work offer more suggestions for modelling studies.