Chemistry and human exposure implications of secondary organic aerosol production from indoor terpene ozonolysis

Abstract

Surface cleaning using commercial disinfectants, which has recently increased during the coronavirus disease 2019 pandemic, can generate secondary indoor pollutants both in gas and aerosol phases. It can also affect indoor air quality and health, especially for workers repeatedly exposed to disinfectants. Here, we cleaned the floor of a mechanically ventilated office room using a commercial cleaner while concurrently measuring gas-phase precursors, oxidants, radicals, secondary oxidation products, and aerosols in real-time; these were detected within minutes after cleaner application. During cleaning, indoor monoterpene concentrations exceeded outdoor concentrations by two orders of magnitude, increasing the rate of ozonolysis under low (<10 ppb) ozone levels. High number concentrations of freshly nucleated sub–10-nm particles (≥10 5 cm −3 ) resulted in respiratory tract deposited dose rates comparable to or exceeding that of inhalation of vehicle-associated aerosols.

The Effect of Human Occupancy on Indoor Air Quality through Real-Time Measurements of Key Pollutants

“…Figure shows the influence of human presence on profiles of VOCs, CO 2 , HONO, J (HONO), NO, NO 2 , O 3 , and OH radicals, in the room on 2021/04/12, during three different periods of the day between 9:30 and 18:00, closed windows (9:40–12:50), open windows (12:50–14:40), and closed windows with turned on air condition (AC) (14:40–18:00). We observed a significant increase of the signal intensities of m / z 56, 58, 68, 70, 72, 82, and 136 during human occupancy, which most likely correspond to 1-butene (C 4 H 8 ), acetone (C 3 H 6 O), isoprene (C 5 H 8 ), methyl vinyl ketone (MVK)/methacrolein (C 4 H 6 O), methylglyoxal (C 3 H 4 O 2 ), 3-methyl furan (3-MF) (C 5 H 6 O) and d -limonene (C 10 H 16 ) (Figure , Figure S4, and Table S2) in agreement with previous studies. , Indeed, isoprene and d -limonene have been identified as the most abundant compounds emitted by exhaled human breath. , For example, Fenske and Paulson reported a mixing ratio of 210 ppb of isoprene exhaled by human breath. A higher mixing ratio of 1-butene of 63 ppb was detected in exhaled human breath compared to other two unsaturated alkenes, ethylene and 1-pentene, with 23 and 21 ppb, respectively.…”

“…It has to be noted that the compound with chemical formula C 10 H 16 O can be also citral, a constituent of cleaning agents or both (DHC and citral), although Figure B shows that the signal intensity of m / z 152 is higher during human occupancy, suggesting that this compound is most likely DHC, at least during the period of human presence in the room. Figure B shows that the highest intensity signal during the human occupancy period corresponds to geranyl acetone ( m / z 194, C 12 H 18 O 2 ), which is typically formed during the surface reaction of ozone with squalene. ,,, A typical compound formed during the ozonolysis of terpenes (e.g., dihydromyrcenol) and ozonolysis of skin lipids is m / z 126, 6-MHO (Figure B). ,,,,,− Intriguingly, the mixing ratio of 6-MHO is higher during the period of human occupancy than the mopping period as was the case with geranyl acetone, indicating that the presence of four adults in the room leads to higher production of secondarily formed 6-MHO through the reaction of O 3 with squalene from the skin than the 6-MHO produced during the reaction of O 3 with terpenes released from the cleaning detergent (Figure B). During the period of mopping and human presence the signal of 4-oxopentanal (4-OPA) arises ( m / z 100 C 5 H 8 O 2 ) (Figure B), which is a typical product compound emerging upon ozonolysis of geraniol, α-terpineol, and linalool ( m / z 154) (Figure A) but it can be also produced by the ozone oxidation of 6-MHO. ,, …”

“…Ozonolysis of d-limonene also generates dihydrocarvone (DHC) (m/z 152 C 10 H 16 O) as a secondary product. 79 It has to be noted that the compound with chemical formula C 10 H 16 O can be also citral, a constituent of cleaning agents 64 or both (DHC and citral), although Figure 4B shows that the signal intensity of m/z 152 is higher during human occupancy, suggesting that this compound is most likely DHC, at least during the period of human presence in the room. Figure 4B shows that the highest intensity signal during the human occupancy period corresponds to geranyl acetone (m/z 194, C 12 H 18 O 2 ), which is typically formed during the surface reaction of ozone with squalene.…”

“…S2) in agreement with previous studies. 1,64 Indeed, isoprene and dlimonene have been identified as the most abundant compounds emitted by exhaled human breath. 65,66 For example, Fenske and Paulson 67 reported a mixing ratio of 210 ppb of isoprene exhaled by human breath.…”

“…Figure 4B shows that the highest intensity signal during the human occupancy period corresponds to geranyl acetone (m/z 194, C 12 H 18 O 2 ), which is typically formed during the surface reaction of ozone with squalene. 4,7,81,64 A typical compound formed during the ozonolysis of terpenes (e.g., dihydromyrcenol) 90 and ozonolysis of skin lipids is m/z 126, 6-MHO (Figure 4B). 79,80,4,7,9,81−85 Intriguingly, the mixing ratio of 6-MHO is higher during the period of human occupancy than the mopping period as was the case with geranyl acetone, indicating that the presence of four adults in the room leads to higher production of secondarily formed 6-MHO through the reaction of O 3 with squalene from the skin than the 6-MHO produced during the reaction of O 3 with terpenes released from the cleaning detergent (Figure 4B).…”