High airborne pollen concentrations are generally associated with daylight hours when it is sunny and warm and plants release pollen into the air (Alcazar et al. 1999; Dahl et al. 2013). In contrast, cooler night-time periods are usually considered to be the time of low-allergy risk. This opinion is often reflected in pollen allergy avoidance strategies presented by the media, where the most commonly repeated recommendation is to stay indoors during the day and plan outdoor activities for the evening. However, there is evidence to suggest that elevated concentrations of airborne pollen might also occur during the evening (e.g. Norris-Hill and Emberlin 1991). So, is the night really a time of low-allergy risk? We present the results of the comparative analysis of pollen concentrations during daytime and night-time hours for five allergenic pollen types (Burbach et al. 2009), i.e. alder (Alnus sp.), birch (Betula sp.), grasses (Poaceae), mugwort (Artemisia sp.) and ragweed (Ambrosia sp.).

中文翻译：

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花粉噩梦：夜间空气中花粉水平升高

空气中花粉浓度高通常与白天阳光明媚、温暖且植物将花粉释放到空气中有关（Alcazar 等人，1999 年；Dahl 等人，2013 年）。相比之下，较冷的夜间时段通常被认为是低过敏风险的时间。这种观点经常反映在媒体提出的避免花粉过敏的策略中，其中最常重复的建议是白天呆在室内，晚上计划户外活动。然而，有证据表明，空气中花粉浓度升高也可能发生在晚上（例如 Norris-Hill 和 Emberlin 1991）。所以，夜晚真的是低过敏风险的时期吗？我们展示了五种过敏性花粉类型（Burbach 等人，2009 年），即桤木 (Alnus sp.)、桦木 (Betula sp.)、禾本科植物 (Poaceae) 在白天和夜间的花粉浓度比较分析结果、艾 (Artemisia sp.) 和豚草 (Ambrosia sp.)。