Effect of Ozone, Clothing, Temperature, and Humidity on the Total OH Reactivity Emitted from Humans

Abstract

People influence indoor air chemistry through their chemical emissions via breath and skin. Previous studies showed that direct measurement of total OH reactivity of human emissions matched that calculated from parallel measurements of volatile organic compounds (VOCs) from breath, skin, and the whole body. In this study, we determined, with direct measurements from two independent groups of four adult volunteers, the effect of indoor temperature and humidity, clothing coverage (amount of exposed skin), and indoor ozone concentration on the total OH reactivity of gaseous human emissions. The results show that the measured concentrations of VOCs and ammonia adequately account for the measured total OH reactivity. The total OH reactivity of human emissions was primarily affected by ozone reactions with organic skin-oil constituents and increased with exposed skin surface, higher temperature, and higher humidity. Humans emitted a comparable total mixing ratio of VOCs and ammonia at elevated temperature-low humidity and elevated temperature-high humidity, with relatively low diversity in chemical classes. In contrast, the total OH reactivity increased with higher temperature and higher humidity, with a larger diversity in chemical classes compared to the total mixing ratio. Ozone present, carbonyl compounds were the dominant reactive compounds in all of the reported conditions.

Keywords: human skin emissions; indoor chemistry; indoor ozone; ozone deposition velocity; volatile organic compounds.

Figure 1

(a) Measured OH reactivity from occupant emissions at steady state. Experiments involved the same four adult volunteers occupying a chamber wearing long clothing or short clothing, under the same conditions on different days. Two replicates were done for the same condition with the same volunteers on different days (n = 2). Ozone was absent (red), introduced to the chamber when VOC reached SS (blue), or introduced to the chamber from the start of the experiment (black). (b) Measured (filled bars) and calculated (empty bars) OH reactivity from occupant emissions at steady state. Each bar corresponds to the mean among SS values between the two replicates conducted for each condition. Error bars indicate the method uncertainties (∼48% for measured reactivity, ∼30% for calculated reactivity). Steady-state values were determined during the last 15 min before occupants left the chamber.

Figure 2

Concentrations of 6-MHO, 4-OPA, and geranyl acetone measured in the chamber occupied from 9:30 by four adults wearing long/short clothing. For each condition, two replicate experiments (N = 2) were conducted (long clothing conditions (6), (21), short clothing conditions (8), (23); see Table S1). The dashed line indicates when ozone was mixed into the chamber air. The dips correspond to measurements of the chamber supply air.

Figure 3

Measured and calculated OH reactivity from four adults occupying the chamber from 9:30, wearing long clothing, exposed to moderate or high temperature (T), and low or high humidity (RH). Ozone was added to the chamber air when occupant emissions reached steady state (dashed vertical line). Total measured and calculated OH reactivities are reported with their associated method uncertainties, 48 and 30%, respectively. 6-MHO, 4-OPA, and geranyl acetone (GA) OH reactivities are reported with the gray area and colored lines, respectively. Missing data points for the first 1.5 h in the bottom panel are due to instrument failure. The dip in the experiment at a high T and a low RH corresponds to the measurement of the chamber supply air.

Figure 4

Speciated total OH reactivity (top row) and speciated total mixing ratios (bottom row) measured at the steady state with O₃ present; four adults wearing long clothing occupied the climate chamber at various temperatures (T) and relative humidities (RH). Total OH reactivities represented in the pie charts in the top row are 32 ± 10, 41 ± 12, and 40 ± 12 s^–1, for the three cases, moderate T and low RH, high T and low RH, and high T and high RH, respectively. Total mixing ratios represented in the pie charts in the bottom row are 190 ± 13, 405 ± 33, and 393 ± 32 ppb, for the three cases, moderate T and low RH, high T and low RH, and high T and high RH, respectively. The size of the pie charts is scaled to the total values, different scales are used between pies representing OH reactivity and pies representing the mixing ratios. Steady-state values were determined during the last 15 min before occupants left the chamber.