The role of ice in N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis at high latitudes

Abstract

Abstract. We report evidence for ice catalyzing N 2 O 5 heterogeneous hydrolysis from a study conducted near Fairbanks, Alaska in November 2007. Mixing ratios of N 2 O 5 , NO, NO 2 , and ozone are reported and are used to determine steady state N 2 O 5 lifetimes. When air masses are subsaturated with respect to ice, the data show longer lifetimes (≈20 min) and elevated N 2 O 5 levels, while ice-saturated air masses show shorter lifetimes (≈6 min) and suppressed N 2 O 5 levels. We also report estimates of aerosol surface area densities that are on the order of 50 µm 2 /cm 3 , a surface area density that is insufficient to explain the rapid losses of N 2 O 5 observed in this study, reinforcing the importance of other reactive surfaces such as ice. Consideration of two possible responsible types of ice surfaces, the snowpack and suspended ice particles, indicates that both are reasonable as possible sinks for N 2 O 5 . Because ice-saturated conditions are ubiquitous in high latitudes, ice surfaces are likely to be a key loss of N 2 O 5 , leading to nitric acid production and loss of NO x in high latitude plumes.

Comparison of N<sub>2</sub>O<sub>5</sub> mixing ratios during NO3Comp 2007 in SAPHIR

“…Other CRDS-instruments typically use an interval for filter changes of a 1 to 4 h in field campaigns (e.g. Apodaca et al, 2008;Crowley et al, 2010). The inlet transmission efficiency needs to be characterised for an individual instrument for different conditions before it is deployed in the field.…”

Heterogeneous Atmospheric Chemistry, Ambient Measurements, and Model Calculations of N2O5: A Review

“…Under such conditions, in situ measurement techniques are critical to determining the N 2 O 5 mixing ratio. At a polluted Arctic site during winter, Apodaca et al (2008) observed N 2 O 5 levels as high as 50-100 ppt. This study and a previous study at similar conditions by Ayers and Simpson (2006) estimated N 2 O 5 lifetimes from below 1 min up to 4 h. These short lifetimes are indicative of a fast, direct loss of N 2 O 5 because NO 3 levels are so low at cold temperatures.…”

“…This parameter has been measured under controlled laboratory conditions on three major types of substrates: ice surfaces, water droplets, and aerosol surfaces. The studies on ice surfaces are of critical importance at high latitudes and in the stratosphere (Tolbert et al 1988;Horn et al 1994;Apodaca et al 2008), whereas the studies on water droplets are thought to be important under foggy conditions (Wood et al 2005;Sommariva et al 2009) and in clouds. Laboratory measurements on those substrates are summarized by Sander et al (2006) and are beyond the scope of this review.…”

“…Simpson and coworkers (Simpson 2003;Ayers et al 2005;Apodaca et al 2008) have undertaken a parallel development of CRDS, using continuous wave (cw) diode lasers rather than a pulsed laser source. These cw CRDS systems have the advantage of much smaller size, weight, and power consumption, making them extremely versatile for use in field campaigns, as illustrated in Figure 5.…”

The fate of NO<sub>x</sub> emissions due to nocturnal oxidation at high latitudes: 1-D simulations and sensitivity experiments

“…Measurements of N 2 O 5 near Fairbanks in winter by our group found that sinks of N 2 O 5 (presumably heterogeneous chemistry) were an efficient mechanism for NO x removal near ground level (Ayers and Simpson, 2006). Apodaca et al (2008) found that dry aerosol surface area was insufficient to explain the loss of N 2 O 5 observed, suggesting loss to other surfaces plays a key role. To characterize the loss to the snowpack, Huff et al (2011) found the deposition velocity of N 2 O 5 to be 0.59 ± 0.47 cm s −1 and that dry deposition represents at least 1/8 of the total chemical removal of N 2 O 5 near the ground.…”