飞机身后的白线为什么有时很快消失，有时越铺越宽？

ice crystals form around the particles emitted from the engine.

配合EPA完整的凝结后冻结机制使用，不将可见白线写成气态水蒸气本身。

A contrail will form if the humidity becomes high enough (and the air temperature becomes low enough) for water vapor to condense on particles (often soot) in the exhaust and the surrounding air to form tiny water droplets, and then these droplets freeze at low temperatures into ice crystals.

对象为喷气发动机排气型凝结尾迹；不包含所有低空作业喷洒、烟或翼面短暂凝结。

Many contrails are short lived and form and evaporate in a matter of seconds-to-minutes due to low humidity conditions in the atmosphere where airplanes are flying. Persistent contrails result when airplanes fly through layers of high humidity conditions (known as super saturated air) in the atmosphere. They can last for a few minutes or longer than a day.

这里高湿指尾迹所在高度的适合冰晶持续条件，不是地面湿度读数；时长是可能范围，不是计时鉴定规则。

there may be high humidity conditions at high altitudes, but low humidity conditions at ground level.

只支持高空与地面不同；不能据地面体感确定当天航路是否形成尾迹。

Contrails can also take different shapes and appearances depending on atmospheric conditions, wind movement, and aircraft flight patterns.

只解释普通尾迹形态与演变；不能仅凭一张白线照片确认个别飞机任务或物质成分。

Persistent contrails can interact with wind and clouds to form cirrus clouds, which are thin, wispy clouds that are common at high altitudes.

只解释普通尾迹形态与演变；不能仅凭一张白线照片确认个别飞机任务或物质成分。

ice crystals form around the particles emitted from the engine.

配合EPA完整的凝结后冻结机制使用，不将可见白线写成气态水蒸气本身。

Aircraft engine exhaust is composed of water vapor, carbon dioxide (CO2), and other emissions

尾迹可见冰晶和发动机排放物清单不是同一概念；不提供个别航班排放量或健康风险评估。