The Impact of Indoor Environments on the Abundance of Urban Outdoor VOCs

With the upcoming transition to clean
electric vehicles, the sources
of volatile organic compounds (VOCs) in the ambient environment are
rapidly changing and highly uncertain. Here, through systematic characterization
of emissions from a typical apartment in a Chinese megacity (Shenzhen),
we show that indoor environments contribute significantly to the levels
of ambient (i.e., outdoor) VOCs. In particular, we observe that the
majority of indoor VOCs originate from unoccupied spaces, demonstrating
temperature-dependent release from indoor surface reservoirs. The
total indoor-to-outdoor VOC emission rates varied from 53 to 2300
mg day–1 (median 230 mg day–1)
during unoccupied periods, influenced by both the air exchange rate
and indoor temperature. Reanalysis of literature data from various
building studies worldwide corroborates our findings and reveals that
indoor-to-outdoor emissions scale with room volume, with an average
emission rate of 0.33 ± 0.03 mg h–1 m–3. Our study implies that indoor-to-outdoor emissions significantly
contribute to urban VOC levels, rivaling traditional urban sources,
e.g., power generation and biomass burning. This is particularly true
for oxygenated VOCs, such as methanol, amounting to ∼60% of
transportation emissions. The findings change our understanding of
the role of indoor VOC contributions to outdoor air quality, whose
importance will increase as controls on industrial and transportation
emissions intensify.

随着全球向清洁电动汽车的转型浪潮逐步临近，大气环境中挥发性有机化合物（Volatile Organic Compounds，VOCs）的来源正快速更迭且具有高度不确定性。本研究通过对中国超大城市深圳一处典型公寓的排放物开展系统性表征分析，发现室内环境对大气（即室外）中VOCs的浓度水平有着显著贡献。具体而言，我们观测到绝大多数室内VOCs源自空置空间，这体现出室内表面储库中VOCs的释放过程与温度呈显著相关性。在无人居住时段，室内向室外的VOC总排放速率介于53至2300 mg·d⁻¹之间（中位数为230 mg·d⁻¹），该速率同时受空气交换率与室内温度的共同影响。对全球范围内多项建筑相关研究的文献数据进行重新分析后，本研究的核心结论得到了佐证，同时发现室内向室外的VOC排放速率与房间体积成正相关，平均排放速率为0.33±0.03 mg·h⁻¹·m⁻³。本研究表明，室内向室外的VOC排放对城市VOC浓度水平有着显著贡献，其影响力可与传统城市排放源（如发电与生物质燃烧）相媲美。对于含氧挥发性有机化合物（Oxygenated VOCs）而言尤其如此，例如甲醇，其排放量约占交通运输排放总量的60%。本研究的发现更新了我们对室内VOCs对室外空气质量贡献作用的认知，随着工业与交通运输排放管控力度不断加强，这一贡献的重要性还将进一步提升。