Abstract
Several studies reported that evaporation of fragrant essential oils in an indoor environment may cause the emission of secondary organic aerosols (SOAs). However, the tendency of forming SOAs from the use of Chinese herbal oils has not been reported. This study investigated the formation of SOAs from various Chinese herbal oils when reacting with ozone in a controlled environment chamber under different test conditions. Lemon oil, a fragrant essential oil, was also tested under the identical experimental conditions for comparison. The results showed that the formation of SOAs from Chinese herbal oils was limited, compared with lemon oil. Of the Chinese herbal oils tested, Chinese mulberry and perillae folium oils produced more SOAs than the other oils. GC/MS analysis of the essential oils demonstrated the presence of SOA precursors, such as d-limonene, in Chinese mulberry and perillae folium oils but not in the other Chinese herbal oils. Compared with the tested Chinese herbal oils, evaporation of 1 mL lemon oil in the presence of 30 ppb ozone may cause an increase of 6.4 μg/m3 in indoor PM level in a typical room or office. This study concluded that the use of Chinese herbal oils tested in this study would result in a lower particle concentration in indoor settings compared with fragrant essential oils.
Highlights
Oil evaporating Ozone injection cm : Chinese mulberry pf : Perillae folium li : Ligusticum an : Angelica pn : PenoyT dt : Dried tangerine peel nr : Notopterygium root lm : Lemon 1.9e+4 1.4e+4 T TT TTT TT T 9.5e+3 5.0e+3cm pf li an pn dt nr lm Essential oilConstituents (Percentage)Lemon limonenea (71.7%), -pinenea (15.6%), -pinenea (1.9%)
When those essential oils were presented with 120 ppb of ozone, lemon oil was observed to have a substantial increase of particle number concentration (p < 0.001) and Chinese mulberry (p = 0.011) and perillae folium (p = 0.002) were the only two Chinese herbal oils with a significant increase in concentration
It can be seen that lemon oil contained terpenes such as limonene, α-pinene and β-pinene, which Hoffmann identified as secondary organic aerosols (SOAs) precursors (Hoffmann et al, 1997)
Summary
Approximately 0.29 mg of particulate matter was produced when 1 mL of lemon oil was presented with 30 ppb of ozone in the small chamber, with the evaporation rate of approximately 20 μg per minute. This means that a room or an office (approximately 45 m3) using 1 mL of lemon oil may cause an increase of 6.4 μg/m3 in PM level. An one-hour massage service using 20 mL of lemon oil will generate 5.8 mg of particulate matter in a spa center. More amount of essential oil will be evaporated and a greater amount of particulate matter will be produced when a room or a spa center using essential oil, such as lemon oil, in the condition of elevated ozone level and/or poor ventilation
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