Influencing Characteristics Of Temperature And Humidity Of Human Upper Respiratory Tract On PM_2.5 Water-soluble Ions And Oxidation Potential

The concentration and composition of PM_2.5 are closely related to the human health risk.PM_2.5 will pass through the respiratory tract before the deposition of the lungs,and the temperature（T）and relative humidity（RH）of the respiratory tract are completely different from the external environment.Therefore,the chemical composition and oxidative potential（OP,including oxidative potential toxicity OP_m and total oxidative potential OP_v）of PM_2.5may change.So it is particularly important to study the influence of temperature and humidity of human upper respiratory tract on PM_2.5 chemical composition(PM_2.5 concentration,concentration and proportion of water-soluble ions,water content（LWC）and its proportion（ω-LWC）,particle acidity（p H）)and OP.In this paper,PM_2.5 in indoor and upper respiratory tract（simulated body temperature and human relative humidity respectively）were sampled from September 7 to December 21,2019,and from October 10,2020 to March 17,2021.The water-soluble ion composition and OP of PM_2.5 were continuously measured and analyzed by using ion chromatograph,ISORROPIAⅡthermodynamic equilibrium model and DTT experiment.The main contents are as follows:（1）The characteristics of the influence of upper respiratory temperature and humidity on the mass proportion of water-soluble ions in PM_2.5 were obtained.During the transmission from indoor to upper respiratory tract,the proportion of water-soluble Ions in PM_2.5 changes with the increase of temperature or relative humidity.As the temperature increases,the mass proportion of SO₄^2-increases from 14.1%in the room to 23.2%in the upper respiratory tract.The mass ratios of NO₃^-and NH₄⁺decreased from 20.6%and 2.4%in the room to 6.8%and0.9%in the upper respiratory tract,respectively.With the increase of relative humidity,the mass ratios of SO₄^2-,NO₃^-and NH₄⁺decreased from 14.2%,14.4%and 2.9%indoors to10.1%,4.5%and 1.1%in the upper respiratory tract,respectively.During the transmission process,with the increase of temperature and humidity,the main water-soluble ion components of PM_2.5 deposited in the body are all SO₄^2-,which indicates that the pollution source of SO₄^2-is the main contributor to the water-soluble ion of PM_2.5 in the body.It is necessary to control the emissions from coal-fired power plants and other sources to reduce people’s exposure to the water-soluble component which accounts for a large proportion of the mass of PM_2.5 deposited in the body.（2）The influence characteristics of upper respiratory temperature and humidity on PM_2.5concentration,moisture content ratio,p H of particle acidity and oxidative potential toxicity OP_m were obtained.From the transmission process of indoor to the upper respiratory tract,when the temperature increases,the PM_2.5 concentrations by containing half volatile substances volatile average falls by 39.8%,the percentage of particle water content decreases by 70%on average because the drop of particle water content is greater than the drop of particle concentration,and the p H of PM_2.5 is also affected by the change of water-soluble ions and the decrease of water content,and the increase of acidity makes the solubility of transition metals such as iron and copper in the particles increase,and the mass proportion of water-soluble ions increases,which leads to the enhancement of PM_2.5 oxidation potential toxicity.When the relative humidity increases,PM_2.5 concentrations rise due to its hygroscopic properties.As the increase of water content is greater than the increase of particle concentration,the average increase of water content is 46.32%.The p H of PM_2.5 is increased by the change of water-soluble ions and the increase of water content,and the acidity is weakened.The mass proportion of water-soluble ions in the transition metal in the particles decreases,and the oxidation potential toxicity of the particles is weakened.（3）The mechanism of the influence of upper respiratory temperature and humidity on particle oxidation potential was explained.Temperature and relative humidity of the upper respiratory tract mainly by influencing the quality of each water soluble ion(especially the main acid component,SO₄^2-and the main alkaline components,NH₄⁺)and the water content ratio make particles p H change（the latter plays a leading role）,which affect the quality of the water-soluble transition metal ions proportion,make the change particle oxidation potential toxicity.At the same time,the upper respiratory temperature and relative humidity also affect the PM_2.5 concentration,and then together with the particle oxidation potential toxicity OP_maffects the particle total oxidation potential OP_v.