Secondary aerosols begin life as gases and chemically react in the atmosphere to form particles.

次生气溶胶最初以气体形态出现，在大气中发生化学反应从而形成颗粒物。

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Secondary aerosolsbegin life as gases and chemically react in the atmosphere to form particles.

二次气溶胶起初表现为各种气体，在大气中发生化学反应后形成颗粒。

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When melting snow crystals or raindrops fall through very cold air, they freeze to form small particles of ice,called sleet.

VOA: special.2010.01.05

When melting snow-crystals or raindrops fall through very cold air, they freeze to form small particles of ice, called sleet.

VOA: special.2011.01.11

Under some conditions, these particles may grow larger and form solid pieces of ice,or hail.

VOA: special.2010.01.05

Nitrogen oxides contribute to haze and form small particles that make people sick and even kill them.

NPR: E.P.A Proposes New Rules on Haze

It is similar to ordinary soap, but the atoms of iron help form tiny particles that are easily removed magnetically.

BBC: Magnetic soap could help in oil spill clean-ups

But at a site 50km east of the eruption, a quarter of the ash falling to the ground was in the form of particles of ten microns or less.

ECONOMIST: Volcanoes and air travel: Small eruption in Iceland | The