Indoor ozone/human chemistry and ventilation strategies

Abstract

This study aimed to better understand and quantify the influence of ventilation strategies on occupant‐related indoor air chemistry. The oxidation of human skin oil constituents was studied in a continuously ventilated climate chamber at two air exchange rates (1 h−1 and 3 h−1) and two initial ozone mixing ratios (30 and 60 ppb). Additional measurements were performed to investigate the effect of intermittent ventilation (“off” followed by “on”). Soiled t‐shirts were used to simulate the presence of occupants. A time‐of‐flight‐chemical ionization mass spectrometer (ToF‐CIMS) in positive mode using protonated water clusters was used to measure the oxygenated reaction products geranyl acetone, 6‐methyl‐5‐hepten‐2‐one (6‐MHO) and 4‐oxopentanal (4‐OPA). The measurement data were used in a series of mass balance models accounting for formation and removal processes. Reactions of ozone with squalene occurring on the surface of the t‐shirts are mass transport limited; ventilation rate has only a small effect on this surface chemistry. Ozone‐squalene reactions on the t‐shirts produced gas‐phase geranyl acetone, which was subsequently removed almost equally by ventilation and further reaction with ozone. About 70% of gas‐phase 6‐MHO was produced in surface reactions on the t‐shirts, the remainder in secondary gas‐phase reactions of ozone with geranyl acetone. 6‐MHO was primarily removed by ventilation, while further reaction with ozone was responsible for about a third of its removal. 4‐OPA was formed primarily on the surfaces of the shirts (~60%); gas‐phase reactions of ozone with geranyl acetone and 6‐MHO accounted for ~30% and ~10%, respectively. 4‐OPA was removed entirely by ventilation. The results from the intermittent ventilation scenarios showed delayed formation of the reaction products and lower product concentrations compared to continuous ventilation.

The Indoor Chemical Human Emissions and Reactivity (ICHEAR) project: Overview of experimental methodology and preliminary results

“…In these four experiments, the rate at which ozone was removed by the empty stainless steel chamber (k chamber ) was determined from the ratio (R) of the steady-state ozone concentration in the chamber to that in the supply air and the ACR (k chamber =(ACR/R)-ACR). The average value for k chamber was 0.17 h -1 (range 0.092-0.29 h −1 ), which is very close to the value reported by Salvador et al 20 for the same chamber (0.15 h −1 ). The chamber surfaces were thus relatively clean and were responsible for only a small fraction of the total ozone removal relative to the ozone in the supply air.…”

“…12 Factors that modify this chemistry include number of occupants, room temperature, relative humidity (RH), ozone concentration, and ventilation rate. 20,32 Model simulations further indicate that the presence of occupants can reduce oxidant concentrations and affect the formation of new products, 22 as was demonstrated for a fixed set of conditions in an earlier chamber study. 33 However, more extensive controlled chamber studies of human emissions, their constituents, and chemical transformations are lacking.…”

“…In this case, the dynamics of the chemistry, especially those of secondary and tertiary products, is expected to be different, as the products of human emissions do not reach steady state before ozone-initiated reactions commence (marked "from start"). 20 Both types of experiments were performed at the lower air temperature and RH, with both "long" and "short" The volunteers were seated in the auxiliary chamber, inhaling ozonefree chamber air and exhaling into the primary (measured) chamber via the breathing masks. After 3 hours, they exited the chamber for a 20-min break.…”

“…[13][14][15][16] They have pointed out the paramount importance of reactions on the human occupant interface, as well as the significant contribution from occupants to the composition of indoor air. [17][18][19][20] Human emissions can undergo chemical transformations and generate a suite of new compounds. 12,21,22 A prime example of such transformations is the ozonolysis of skin lipid constituents, especially squalene.…”

“…13,14,[23][24][25][26][27] These reactions also occur on clothing, which acquire skin oils during wear. 20,[28][29][30][31] The products partition between the gas phase and surfaces. Some of them stay on the skin, while others can deposit on other indoor surfaces and become precursors for subsequent secondary reactive chemistry.…”