Production of HONO from NO2 uptake on illuminated TiO2 aerosol particles and following the illumination of mixed TiO2/ammonium nitrate particles
Production of HONO from NO2 uptake on illuminated TiO2 aerosol particles and following the illumination of mixed TiO2/ammonium nitrate particles
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DOI：
10.5194/acp-21-5755-2021
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发表时间：
2021-04-16
影响因子：
6.3
通讯作者：
Heard, Dwayne E.
中科院分区：
文献类型：
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作者：
Dyson, Joanna E.;Boustead, Graham A.;Heard, Dwayne E.
利用与光碎裂激光诱导荧光检测装置耦合的气溶胶流动管系统，测量了在NO2存在的情况下，由照射的二氧化钛气溶胶产生HONO的速率。当NO2与伽马(NO2->；HONO)的混合比在34-400 ppb范围内时，测定了NO2反应吸收系数以形成HONO，伽马(NO2->；HONO)。在相对湿度为15+/-1%时，灯的光化通量为(1.63+/-0.09)x 10(16)光子厘米(-2)S(-1)(积分在290到400 nm之间)，这与中午的环境光化通量值相似。在低NO2下，γ(NO2->；HONO)随着NO2混合比的增加而增加，在接近51 ppb NO2时，在(1.26+/-0.17)×10(-4)处达到峰值，然后在较高NO2混合比时急剧下降，而不是趋于平缓，这表明表面饱和。此外，还研究了相对湿度对HONO生成量的影响，发现在相对湿度为25%时，二氧化钛气溶胶表面的HONO生成量出现一个峰值。用零维动态盒模型研究了与观测到的HONO生成和反应吸收系数的趋势相一致的可能机理。模拟研究支持了涉及两个NO2分子的气溶胶表面HONO的产生机制，以及依赖于NO2的表面HONO损失机制。在另一项单独的实验中，观察到在没有NO2的情况下，硝酸盐/二氧化钛混合气溶胶的照明产生了大量的HONO。然而，仅从硝酸盐气溶胶的光照下看不到HONO的产生。观测到的硝酸盐/二氧化钛混合气溶胶产生HONO的速率与佛得角大气观测站在遥远的热带海洋边界层发现的环境条件进行了比对。含有光催化剂的气溶胶颗粒硝酸盐光解生成HONO的速率被发现与在CVAO再现观测到的HONO浓度所必需的HONO生成速率相似。这些结果证明，颗粒硝酸盐的光解作用可能对HONO的产生产生重大影响，从而对海洋边界层中NOx的产生产生重大影响，因为海洋边界层中存在含有硝酸盐的混合气溶胶和在尘埃中发现的诸如TiO2光催化物种。
The rate of production of HONO from illuminated TiO2 aerosols in the presence of NO2 was measured using an aerosol flow tube system coupled to a photo-fragmentation laser-induced fluorescence detection apparatus. The reactive uptake coefficient of NO2 to form HONO, gamma(NO2 -> HONO), was determined for NO2 mixing ratios in the range 34-400 ppb, with gamma(NO2 -> HONO) spanning the range (9.97 +/- 3.52) x 10(-6) to (1.26 +/- 0.17) x 10(-4) at a relative humidity of 15 +/- 1% and for a lamp photon flux of (1.63 +/- 0.09) x 10(16) photons cm(-2) s(-1) (integrated between 290 and 400 nm), which is similar to midday ambient actinic flux values. gamma(NO2 -> HONO) increased as a function of NO2 mixing ratio at low NO2 before peaking at (1.26 +/- 0.17) x 10(-4) at similar to 51 ppb NO2 and then sharply decreasing at higher NO2 mixing ratios rather than levelling off, which would be indicative of surface saturation. The dependence of HONO production on relative humidity was also investigated, with a peak in production of HONO from TiO2 aerosol surfaces found at similar to 25% RH. Possible mechanisms consistent with the observed trends in both the HONO production and reactive uptake coefficient were investigated using a zero-dimensional kinetic box model. The modelling studies supported a mechanism for HONO production on the aerosol surface involving two molecules of NO2, as well as a surface HONO loss mechanism which is dependent upon NO2. In a separate experiment, significant production of HONO was observed from illumination of mixed nitrate/TiO2 aerosols in the absence of NO2. However, no production of HONO was seen from the illumination of nitrate aerosols alone. The rate of production of HONO observed from mixed nitrate/TiO2 aerosols was scaled to ambient conditions found at the Cape Verde Atmospheric Observatory (CVAO) in the remote tropical marine boundary layer. The rate of HONO production from aerosol particulate nitrate photolysis containing a photocatalyst was found to be similar to the missing HONO production rate necessary to reproduce observed concentrations of HONO at CVAO. These results provide evidence that particulate nitrate photolysis may have a significant impact on the production of HONO and hence NOx in the marine boundary layer where mixed aerosols containing nitrate and a photocatalytic species such as TiO2, as found in dust, are present.