Heterogeneous reaction of peroxyacetic acid and hydrogen peroxide on ambient aerosol particles under dry and humid conditions: kinetics, mechanism and implications

Abstract

Abstract.Hydrogen peroxide (H 2 O 2 ) and organic peroxides play important roles in the cycle of oxidants and the formation of secondary aerosols in the atmosphere. Recent field observations have suggested that the budget of peroxyacetic acid (PAA, CH 3 C(O)OOH) is potentially related to the aerosol phase processes, especially to secondary aerosol formation. Here, we present the first laboratory measurements of the uptake coefficient of gaseous PAA and H 2 O 2 onto ambient fine particulate matter (PM 2.5 ) as a function of relative humidity (RH) at 298 K. The results show that the PM 2.5 , which was collected in an urban area, can take up PAA and H 2 O 2 at the uptake coefficient (γ ) of 10 −4 , and both γ PAA and γ H 2 O 2 increase with increasing RH. The value of γ PAA at 90 % RH is 5.4 ± 1.9 times that at 3 % RH, whereas γ H 2 O 2 at 90 % RH is 2.4 ± 0.5 times that at 3 % RH, which suggests that PAA is more sensitive to the RH variation than H 2 O 2 is. Considering the larger Henry's law constant of H 2 O 2 than that of PAA, the smaller RH sensitivity of the H 2 O 2 uptake coefficient suggests that the enhanced uptake of peroxide compounds on PM 2.5 under humid conditions is dominated by chemical processes rather than dissolution. Considering that mineral dust is one of the main components of PM 2.5 in Beijing, we also determined the uptake coefficients of gaseous PAA and H 2 O 2 on authentic Asian Dust storm (ADS) and Arizona Test Dust (ATD) particles. Compared to ambient PM 2.5 , ADS shows a similar γ value and RH dependence in its uptake coefficient for PAA and H 2 O 2 , while ATD gives a negative dependence on RH. The present study indicates that, in addition to the mineral dust in PM 2.5 , other components (e.g., soluble inorganic salts) are also important to the uptake of peroxide compounds. When the heterogeneous reaction of PAA on PM 2.5 is considered, its atmospheric lifetime is estimated to be 3.0 h on haze days and 7.1 h on non-haze days, values that are in good agreement with the field observations.

Observation of atmospheric peroxides during Wangdu Campaign 2014 at a rural site in the North China Plain

“…Using the box model, the daily-averaged lifetime of atmospheric H 2 O 2 , MHP and PAA during the whole of Phase I and Phase III were calculated to be about 2.1, 2.3 and 3.0 h, respectively. This is comparable to the literature results with the inclusion of heterogeneous reaction (Liang et al, 2013b;Wu et al, 2015), but notably shorter than the recent studies conducted by Khan et al (2015) and Nguyen et al (2015) without the coupling of the heterogeneous process. Although dry deposition is thought to dominate the atmospheric lifetime of peroxides in previous studies (Reeves and Penkett, 2003), its role in the lifetime of atmospheric peroxides is insignificant during Wangdu Campaign 2014.…”

“…During these case study phases, 75 % of the wind speed data were ≤ 2.2 m s −1 and the mean value was 1.6 m s −1 . It has been shown that the atmospheric lifetimes of peroxides are on the order of several hours as reported previously Wu et al, 2015), implying that the effect of regional transport or dilution on the concentrations of atmospheric peroxides was of little significance over Wangdu. Hence, the regionalscale transport can be excluded in our box model and the budgets of peroxides are, to a large extent, dependent on local chemical processes during the observation.…”

“…The uptake coefficient of 1×10 −3 approached the upper limit of the laboratory measured value for H 2 O 2 on mineral dust (9×10 −4 ) reported by Pradhan et al (2010), but a little higher than the previous measured values on ambient PM 2.5 of (1-5) ×10 −4 during the summertime over urban Beijing . It is reasonable as Wu et al (2015) pointed out that the uptake coefficients for H 2 O 2 and organic peroxides on ambient PM 2.5 are in the same range and show no obvious differences between daytime and nighttime or between non-hazy and hazy conditions.…”

“…Heterogeneous uptake by atmospheric aerosols is recognized as another significant sink for peroxides in the troposphere, especially in dusty and polluted urban areas (Y. Wu et al, 2015).…”

Insights into HO<sub><i>x</i></sub> and RO<sub><i>x</i></sub> chemistry in the boreal forest via measurement of peroxyacetic acid, peroxyacetic nitric anhydride (PAN) and hydrogen peroxide

“…The first-order rate constants representing dry deposition are d PAN and d PAA . Experimental work (Wu et al, 2015) on the uptake of PAA to ambient aerosol indicates an uptake coefficient (γ ) of ≈ 3 × 10 −4 . Using the simplified expression (1) for the heterogeneous loss-rate constant (k het ) of a trace gas to an aerosol particle:…”