PM2.5是指大气中直径小于或等于2.5微米的颗粒物，也称为

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PM2.5是指大气中直径小于或等于2.5微米的颗粒物，也称为可入肺颗粒物。目前北京PM2.5的主要来源有机动车、电厂、锅炉、扬尘、秸秆焚烧等。大风和上升气流有利于污染物的扩散。图为北京某日5次观测到的近地面气温垂直分布示意图。回答下列问题。

一年中，北京春季的PM2.5浓度较高，主要由于

A．沙尘天气和局地扬尘频繁	B．机动车的尾气排放量大
C．农村大量焚烧秸秆	D．燃煤使用量大

依据图11所示气温分布，该日有利于 PM2.5浓度降低的时段是

A．5时至8时	B．8时前后
C．12时至15时	D．5时至20时

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