摘要：Air pollution is a major problem in modern society. These substances include various gases and tiny particles or particles that harm plants, human health and damage the environment. Particulate Matter (PM) is the term for particles found in the air, including dust, soot, dirt, smoke and liquid droplets. Particulates can be suspended in the air for long periods of time. Particulate Matter (PM) is of localized importance near roads, quarries, cement works and other industrial areas. Apart from screening out sunlight, dust on leaf blocks stomata and lowers their conductance to CO2, simultaneously interfering with photosystem II. Polluting gases such as SO2 and NOx enter leaves through stomata, following the same diffusion pathway as CO2. NOx dissolves in cells and gives rise to nitrite ions (NO2, toxic at high concentrations) and nitrate ions (NO3) that enter into nitrogen metabolism as if they had been absorbed through the roots. In some cases, exposure to pollutant gases, particularly SO2, causes stomatal closure which protects the leaf against the further entry of the pollutant but also curtails photosynthesis. In the cells, SO2 dissolves to give bisulfite and sulfite ions; sulfite is toxic but at low concentrations it is metabolized by chloroplasts to sulfate which is not toxic.
