Here in Arizona, says Beamer, where we leave our windows open most of the year and have an arid climate, we would probably have a higher ratio. Industrial centers or sooty cities have plenty of dust too, though for different reasons.
arid adj. 干旱的;不毛的
ratio n. 比例
Theres not much to fret about in simple particles of dirt or organic materials such as pollen , but lead, arsenic and DDT can be a more serious matter. About one-third of the arsenic in the atmosphere comes from natural sources volcanoes principally. The rest comes from mining, smelting, burning fossil fuels and other industrial processes. Even in relatively low concentrations, arsenic is not without risk, especially to small children who play on the floor and routinely transfer things from their hands to their mouths. The same is true for lead, which comes less from wall paint the source most people would expect than from auto exhaust, smelting and soil deposits. Lead loading on floors is a key determinant of blood-lead levels in children, Layton and Beamer wrote in their paper.
fret about 因 焦急;为 烦恼
particle n. 颗粒;微粒
pollen n. 花粉
low concentration 低浓度
determinant adj. 决定性的 n. 决定因素
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