Abstract
Abstract. Understanding the sources of volatile organic compounds (VOCs) is essential for ground-level ozone and secondary organic aerosol (SOA) abatement measures. We made VOC measurements at 27 sites and online observations at an urban site in Beijing from July 2009 to January 2012. Based on these measurement data, we determined the spatial and temporal distribution of VOCs, estimated their annual emission strengths based on their emission ratios relative to carbon monoxide (CO), and quantified the relative contributions of various sources using the chemical mass balance (CMB) model. These results from ambient measurements were compared with existing emission inventories to evaluate the spatial distribution, species-specific emissions, and source structure of VOCs in Beijing. The measured VOC distributions revealed a hotspot in the southern suburban area of Beijing, whereas current emission inventories suggested that VOC emissions were concentrated in downtown areas. Compared with results derived from ambient measurements, the annual inventoried emissions of oxygenated VOC (OVOC) species and C2–C4 alkanes may be underestimated, while the emissions of styrene and 1,3-butadiene may be overestimated by current inventories. Source apportionment using the CMB model identified vehicular exhaust as the most important VOC source, with the relative contribution of 49%, in good agreement with the 40–51% estimated by emission inventories. The relative contribution of paint and solvent utilization obtained from the CMB model was 14%, significantly lower than the value of 32% reported by one existing inventory. Meanwhile, the relative contribution of liquefied petroleum gas (LPG) usage calculated using the CMB model was 6%, whereas LPG usage contribution was not reported by current emission inventories. These results suggested that VOC emission strengths in southern suburban area of Beijing, annual emissions of C2–C4 alkanes, OVOCs and some alkenes, and the contributions of solvent and paint utilization and LPG usage in current inventories all require significant revisions.
Highlights
Volatile organic compounds (VOCs) play important roles in atmospheric chemistry because they can be photochemically oxidized to form ground-level ozone (O3) and secondary organic aerosols (SOAs) (Seinfeld and Pandis, 2006)
The regional measurements in Beijing were conducted during periods with wind speeds < 1.5 m s−1, and the spatial distribution of measured VOC mixing ratios could to some extent reflect the spatial patterns of VOC emission strengths
The emission inventories reported by Tang et al (2010) and Wang et al (2009) suggested that nonmethane VOCs (NMVOCs) and NOx emissions in Beijing were concentrated in downtown areas, with emission strengths that exceeded those in suburban areas by factors of ∼ 5–20
Summary
Volatile organic compounds (VOCs) play important roles in atmospheric chemistry because they can be photochemically oxidized to form ground-level ozone (O3) and secondary organic aerosols (SOAs) (Seinfeld and Pandis, 2006). The spatial distribution of NMVOC emissions in Beijing reported by Zhang et al (2009) illustrated that the largest emission strengths were in southern areas, whereas Zhao et al (2012) suggested that NMVOC emissions were mainly concentrated in the downtown area. In contrast with industrial emissions, the residential emissions contribution reported by Zhang et al (2009) was 16 %, significantly lower than the value of 41 % reported by Zhao et al (2012) These comparisons among different emission inventories revealed the uncertainty of NMVOC emissions in Beijing. Since the measured concentration of NMVOCs is the result of emissions after physical (transport/mixing/deposition) and chemical transformations, various approaches need to be employed to build relationships between measurements and emissions
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