Answer:1. Introduction
The main air pollutants are represented by gases forms, particles in suspension, different ionizing radiation and noise.
The gases forms are: oxidized and reduced forms of carbon (CO2, CO, CH4), of nitrogen (NO2, NO, N2O4, NH3, NH4+), SO2, O3, C6H6 vapours, Hg, volatile phenols, Cl2, etc.
The particulate forms are: PM10 and PM2.5 particulate matter, heavy metals with toxic effect (Pb, Ni, Cd, As), polycyclic aromatic hydrocarbons PAHs, etc.
Atmospheric pollutants have a negative effect on the plants; they can have direct toxic effects, or indirectly by changing soil pH followed by solubilization of toxic salts of metals like aluminum. The particulate matters have a negative mechanical effect. They cover the leaf blade reducing light penetration and blocking the opening of stomata. These impediments influence strongly the process of photosynthesis which rate declines sharply.
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