#粒子形成气态氨(NH_3美元)是一个基础,因此,倾向于接受质子。首先我们有酸(盐酸H_2SO_4美元,HNO_3,美元$ $),物质往往反应酸(二氧化硫,美元NO_2美元),或水滴pH值较低(因为溶解酸)在大气中。与这些酸和氨然后_comes together_接受质子酸。现在protonized氨(铵,美元NH_4 ^ + $)和deprotonized酸(如美元NO_3 ^ -美元)不再是气态,但固体(超细粒子或粒子成核模式)或溶解在水滴(最大分数)。水滴可以视为湿颗粒。下图显示了这个过程的氨和硝酸(由二氧化氮)。[![在这里输入图像描述][1]][1]_Image标题:绿颜色的字体的化合物是位于(主要是湿)粒子表面或溶解在水里滴。化合物用黑颜色的字体是气态的。第二个箭头是失踪的箭头连接气体HNO_3和particle-bounds HNO_3美元美元。 Gaseous $NH_3$ is missing in this figure._ Because this proton-exchange favorably takes place at surfaces or in droplets, these particles grow (see below). # atmospheric particles An exemplary particle size distribution is shown below (_own work ([Neumann, 2016, Fig. 2.1](http://nbn-resolving.de/urn:nbn:de:gbv:18-81508)) but content based on Seinfeld and Pandis (2006a, Fig. 2.7,p.59) which is based on Whitby and Cantrell (1976)_). The Y-axis shows particle abundance (roughly; please see Fig 2.2 in the linked document above for details). [![enter image description here][2]][2] The major source of the coarse particles on the right are primary emissions of particles (dust, sea salt, ...). The accumulation mode particles in the center are partly caused by primary emissions (fine sea salt, combustion processes, ...) and partly grown from smaller particles (Aitken mode or ultra-fine particles). Actually, the ultra-fine particles are grown from so called nucleation mode particles by the condensation of further atmospheric gaseous compounds. The nucleation mode is missing here (and merged with the Aitken mode). Nucleation mode particles are those particles, which are formed by ammonia and atmospheric acids. Other sources for these nucleation mode particles are gaseous organic compounds, which lump together to form particles. The latter particles are also called SOA (secondary organic aerosol). Isoprene is one of the compounds that forms SOA. # health impacts When we combine air polluted by combustion emissions ($NO_X$) with air affected by agricultural emissions, we can expect the formation of ammonium nitrate particles ($NH_4^+$ + $NO_3^-$). Ammonium nitrate can irritate the eyes, nose and lungs. As stated in a comment and to the best of my knowledge, ammonium nitrate particles are not as harmful as e.g. fine soot particles. But I am not a expert on this field. Ammonium sulfate (from $SO_2$ from combustion emissions) have been shown to have negative health impacts on the respiratory system but also on the cardiovascular system (heart etc.; if the particles are sufficiently small to pierce the lung-blood barrier). Ultra fine ammonium nitrate particles can be nuclei for condensation of further gaseous compounds -- e.g. VOC (volatile organic compounds) --, which might have harmful impacts on our respiratory system. # notes Commonly, atmospheric particles are not dry spheres/lumps of matter but somehow associated with water: water droplets with dissolved compounds or a solid core with water _attached_ to the surface; whereas dissolved compounds might be dissolved in the water of the latter type. The atmospheric life time of gaseous acids is very short because they tend to get attached to water (and deprotonize -- reducing the pH value of the water). Partly, the reaction from precursors to acids takes place in the wet particle/droplet phase. E.g. most of produced sulfuric acid ($H_2SO_4$) takes place in the wet phase. # tl;dr Thus, we generate particles by combining ammonia with atmospheric acids. References: - Seinfeld and Pandis, 2006: _Atmospheric Chemistry and Physics: From Air Pollution to Climate Change_. - Whitby and Cantrell, 1976: _Fine particles_ in _Proc. Int. Conf. Environ. Sens. and Asses_. [1]: https://i.stack.imgur.com/2ebkv.png [2]: https://i.stack.imgur.com/U037z.png