Distribution And Source Of Water-Soluble Inorganic Ions In Urban Plant Leaf Particles

Atmospheric particulates can damage the human respiratory system and seriously endanger human health.Atmospheric particles?especially fine particles?have been the primary pollutants that affect the quality of our urban environment and endanger people's health.Most of the substances that have carcinogenic risks to the human body accumulate in particulate matter.In recent years,urban plants have been widely recognized as an important means of reducing atmospheric particulate pollution.As an important part of the urban ecological environment,urban plants can accumulate atmospheric particulates through their rough,moist foliage,thus reducing atmospheric pollution.The water-soluble inorganic ions in the airborne particles are one of the important components of the particulate matter,which can acidify atmospheric precipitation,change the atmospheric radiation balance,and can also synergize with atmospheric toxic organic substances?such as PAHs?and enhance the toxic effects of atmospheric particulates.Since water-soluble inorganic ions are mainly distributed in fine particles with a particle size of less than 10?m,they are beneficial to the absorption of leaf pores.The particle size characteristics of different types of plant leaf retentate particles are different,which may lead to differences in the distribution of water-soluble inorganic ions in the plant leaf particles.Therefore,this study used Nanjing as a research area to carry out the spatio-temporal distribution and interspecies differences of water-soluble inorganic ions in plant leaf particles,and analyzed the potential sources of water-soluble inorganic ions in leaf particles of urban and suburban plants in Nanjing and discussed the relationship between leaf surface micro-characteristics and the content of water-soluble inorganic ions in leaf particles.The main findings were as follows:?1?The total content of water-soluble inorganic ions in the leaf surface particles of common greening plants in five functional areas in Nanjing was between 48.60 mg/g and 96.98 mg/g.The average level of water-soluble inorganic ion concentration was SO₄^2->Na⁺>NO₃^->Ca²⁺>Cl^->Mg²⁺>K⁺>NH₄⁺>F^-.The ion composition was dominated by SO₄^2-,Na⁺,NO₃^-and Ca²⁺,accounting for 86.9%of the total ion content.The concentration of water-soluble inorganic ions in transportation hubs and chemical area were high,especially SO₄^2-and NO₃^-.There was a significant difference in Na⁺content among the plant leaf particles between functional areas.The section of Saihongqiao overpass reaches 27.38 mg/g;followed by the chemical industry area,reaching 20.02 mg/g;the scenic area has the lowest,which is 9.54 mg/g.The content of Ca²⁺in the transportation hub?7.35 mg/g?was the highest,and it was not significantly different between the chemical area?5.98 mg/g?,the residential area?5.78 mg/g?and the culture and education areas?5.02 mg/g?,the lowest content was in the scenic area?2.22 mg/g?.The correlation analysis of water-soluble inorganic ion content in Nanjing showed that there was significant correlation between SO₄^2-,NO₃^-and NH₄⁺content?P<0.05?,indicating that the three secondary ions had certain homology.?2?The total content of water-soluble inorganic ions in the leaf particles of plants in the section of Xinzhuang overpass in Nanjing showed the following characteristics:winter>spring>autumn>summer,and winter was significantly higher than summer.The content of SO₄^2-was significantly higher in winter and spring than in summer and autumn;the contents of Na⁺,Ca²⁺,Mg²⁺and NH₄⁺were significantly higher in winter than in summer;the content of Cl^-and NO₃^-were significantly higher in autumn and winter than in spring and summer;the content of K⁺in winter was significantly higher than the other three seasons;the F^-content was highest in autumn and lowest in summer.According to Pearson's correlation analysis,the correlation between NO₃^-and SO₄^2-was low in winter,and NO₃^-was significantly correlated with NH₄⁺in winter?P<0.05?,indicating that exhaust emissions from motor vehicles in winter were not major contributors to SO₄^2-.It is the main contributor to NH₄⁺and NO₃^-.In winter,Na⁺,Ca²⁺and Mg²⁺ions were significantly correlated with each other at the 0.01 level,while NH₄⁺and SO₄^2-were significantly correlated in the spring;Na⁺and Cl^-were both significantly correlated in the four seasons.?3?The total content of water-soluble inorganic ions in the leaf surface particles of five kinds of green plants showed the highest in Osmanthus fragrans,the lowest in Photinia.Photinia sorbifolia had a strong ability to retain the foliage particles,but it showed a low water-soluble inorganic ion content value.The content of NO₃^-in Fatsia japonica?13.04 mg/g?and Osmanthus fragrans?12.56 mg/g?leaf particles were significantly higher than that of Cinnamomum camphora?11.63 mg/g?,Pittosporum tobira?4.39 mg/g?,and Photinia fraseri?3.50 mg/g?.SO₄^2-was highest in Osmanthus fragrans?61.40 mg/g?and lowest in Photinia?20.10 mg/g?.Na⁺in the foliar particles of Cinnamomum camphora?1.24 mg/g?and Osmanthus fragrans?1.39 mg/g?were significantly higher than other three plants.Ca²⁺was the highest in the foliar particles of Cinnamomum camphora?10.79 mg/g?and Osmanthus fragrans?11.44 mg/g?,and lowest in the foliar particles of Photinia?3.47 mg/g?.With the exception of K⁺,the content of water-soluble inorganic ions in surface particles of Pittosporum was higher than that of Photinia.The correlation analysis of specific leaf area,stomatal density,leaf wax and total water-soluble inorganic ion content in the five kinds of plants showed that the leaf wax content and the total content of water-soluble inorganic ions in the leaf surface particles were significant correlated at0.05 level.There was no significant correlation between stomatal density,specific surface area and the total content of water-soluble inorganic ions in the leaf surface particles.?4?The ratios of water-soluble inorganic NO₃^-/SO₄^2-ratio in leaf particles of urban and suburban areas in Nanjing were not significantly different?0.20 and 0.21 respectively?.The concentration and ratio of NO₃^-and SO₄^2-in the particulate matter in the traffic area were higher than those in other sampling areas.The NO₃^-and SO₄^2-emissions were higher than in urban areas.There were 3 types of sources of water-soluble inorganic ions in the plant leaf particulates in the main urban area of Nanjing City.One was the source of transportation,the other was the source of coal and biomass,the third was the source of dust.Sources of water-soluble inorganic inorganic pollutants in the suburbs were divided into two categories.The first was the source of aerosol and coal,the second was the source of soil and sea salt.