Impact of temperature-driven cycling of hydrogen peroxide (H 2 O 2 ) between air and snow on the planetary boundary layer (original) (raw)
Related papers
Atmospheric Environment, 2002
Tower-based measurements of hydrogen peroxide (H 2 O 2 ) and formaldehyde (HCHO) exchange were performed above the snowpack of the Greenland ice sheet. H 2 O 2 and HCHO fluxes were measured continuously between 16 June and 7 July 2000, at the Summit Environmental Observatory. The fluxes were determined using coil scrubber-aqueous phase fluorometry systems together with micrometeorological techniques. Both compounds exhibit strong diel cycles in the observed concentrations as well as in the fluxes with emission from the snow during the day and the evening and deposition during the night. The averaged diel variations of the observed fluxes were in the range of +1.3 Â 10 13 molecules m À2 s À1 (deposition) and À1.6 Â 10 13 molecules m À2 s À1 (emission) for H 2 O 2 and +1.1 Â 10 12 and À4.2 Â 10 12 molecules m À2 s À1 for HCHO, while the net exchange per day for both compounds were much smaller. During the study period of 22 days on average ð0:8 þ4:6 À4:3 Þ Â 10 17 molecules m À2 of H 2 O 2 were deposited and ð7:0 þ12:6 À12:2 Þ Â 10 16 molecules m À2 of HCHO were emitted from the snow per day. A comparison with the inventory in the gas phase demonstrates that the exchange influences the diel variations in the boundary layer above snow covered areas. Flux measurements during and after the precipitation of new snow shows that o16% of the H 2 O 2 and more than 25% of the HCHO originally present in the new snow were available for fast release to the atmospheric boundary layer within hours after precipitation. This release can effectively disturb the normally observed diel variations of the exchange between the surface snow and the atmosphere, thus perturbing also the diel variations of corresponding gas-phase concentrations. r
Impacts of snowpack emissions on deduced levels of OH and peroxy radicals at Summit, Greenland
Atmospheric Environment, 2002
Levels of OH and peroxy radicals in the atmospheric boundary layer at Summit, Greenland, a location surrounded by snow from which HO x radical precursors are known to be emitted, were deduced using steady-state analyses applied to ðOH þ HO 2 þ CH 3 O 2 Þ; ðOH þ HO 2 Þ; and OH-HO 2 cycling. The results indicate that HO x levels at Summit are significantly increased over those that would result from O 3 photolysis alone, as a result of elevated concentrations of HONO, HCHO, H 2 O 2 ; and other compounds. Estimated midday levels of ðHO 2 þ CH 3 O 2 Þ reached 30-40 pptv during two summer seasons. Calculated OH concentrations averaged between 05:00 and 20:00 (or 21:00) exceeded 4 Â 10 6 molecules cm À3 ; comparable to (or higher than) levels expected in the tropical marine boundary layer. These findings imply rapid photochemical cycling within the boundary layer at Summit, as well as in the upper pore spaces of the surface snowpack. The photolysis rate constants and OH levels calculated here imply that gas-phase photochemistry plays a significant role in the budgets of NO x ; HCHO, H 2 O 2 ; HONO, and O 3 ; compounds that are also directly affected by processes within the snowpack. r
Formaldehyde and hydrogen peroxide in air, snow and interstitial air at South Pole
Atmospheric Environment, 2004
Average H 2 O 2 (HCHO) mixing ratios measured above the snowpack at South Pole were 278 pptv (103 pptv) in December 2000 and between 4 to 43 times (1.4 to 2.6) the expected value based on gas-phase photostationary state model calculations. The larger difference is realized if dry deposition of both species is included in the model. H 2 O 2 and HCHO fluxes from the snowpack were independently determined from gradient measurements in the air above the snow surface, from firn air measurements and from the temporal concentration changes in near-surface snow. On average, the snowpack at South Pole was releasing on the order of 1 x 10 13 and 2 x 10 12 molecules m -2 s -1 of H 2 O 2 and HCHO, respectively, in December 2000. This is consistent with the volumetric fluxes needed for the photostationary state model to reproduce the observed atmospheric mixing ratios of both H 2 O 2 and HCHO. The highly elevated levels of both species found in firn air further support the above estimates.
Atmosphere-to-snow-to-firn transfer studies of HCHO at Summit, Greenland
Geophysical Research Letters, 1999
Formaldehyde (HCHO) measurements in snow, firn, atmosphere, and air in the open pore space of the firn (firn air) at Summit, Greenland, in June 1996 show that the top snow layers are a HCHO source. HCHO concentrations in fresh snow are higher than those in equilibrium with atmospheric concentrations, resulting in HCHO degassing in the days to weeks following snowfall. Maximum HCHO concentrations in firn air were 1.5-2.2 ppbv, while the mean atmospheric HCHO concentration 1 m above the surface was 0.23 ppbv. Apparent HCHO fluxes out of the snow are a plausible explanation for the discrepancy between the 0.1 ppbv atmospheric concentration predicted by photochemical modeling and the measurements. HCHO in deeper firn is near equilibrium with the lower tropospheric HCHO concentration at the annual average temperature. Thus HCHO in ice may in fact be linearly related to multiyear average atmospheric concentrations through a temperature dependent partition coefficient.
Journal of Geophysical Research, 2003
1] Sensitivity studies with physically based numerical air-snow-firn transfer models for formaldehyde (HCHO) and hydrogen peroxide (H 2 O 2 ) show that even though nonlinear processes determine the preservation of HCHO and H 2 O 2 in snow and firn, changes in atmospheric mixing ratios are linearly recorded in ice cores under otherwise constant environmental conditions. However, temperature, snowpack ventilation, and rate and timing of snow accumulation also affect the ice core records of reversibly deposited species and must be considered when inferring past atmospheric mixing ratios. The results of the sensitivity studies allow quantitative separation of these factors in ice core records. Past temperatures and accumulation rates are generally determined in ice cores and the preservation of HCHO and H 2 O 2 is not highly sensitive to snowpack ventilation, leaving changes in seasonality of snow accumulation as the main source of uncertainty in a reconstruction of past atmospheric mixing ratios.
Diel variations of H 2 O 2 in Greenland: A discussion of the cause and effect relationship
Journal of Geophysical Research, 1995
Atmospheric hydrogen peroxide (H202) measurements at Summit, Greenland, in May-June, 1993 exhibited adiel variation, with afternoon highs typically 1-2 parts per billion by volume (ppbv) and nighttime lows about 0.5 ppbv lower. This variation closely followed that for temperature; specific humidity exhibited the same general trend. During a 17-day snowfall-free period, surface snow was accumulating H202, apparently from nighttime cocondensation of H20 and H202. Previous photochemical modeling (Neftel et al., 1995) suggests that daytime H202 should be about 1 ppbv, significantly lower than our measured values.
Atmosphere - to - snow - to - firn transfer studies of HCHO at Summit
2000
Formaldehyde (HCHO) measurements in snow, firn, atmosphere, and air in the open pore space of the firn (firn air) at Summit, Greenland, in June 1996 show that the top snow layers are a HCHO source. HCHO concentrations in fresh snow are higher than those in equilibrium with atmospheric concentrations, resulting in HCHO degassing in the days to weeks following snowfall. Maximum HCHO concentrations in firn air were 1.5-2.2 ppbv, while the mean atmospheric HCHO concentration 1 m above the surface was 0.23 ppbv. Apparent HCHO fluxes out of the snow are a plausible explanation for the discrepancy between the 0.1 ppbv atmospheric concentration predicted by photochemical modeling and the measurements. HCHO in deeper firn is near equilibrium with the lower tropospheric HCHO concentration at the annual average temperature. Thus HCHO in ice may in fact be linearly related to multiyear average atmospheric concentrations through a temperature dependent partition coefficient.
Atmospheric Environment, 2002
Measurements at Summit, Greenland, performed from June-August 1999, showed significant enhancement in concentrations of several trace gases in the snowpack (firn) pore air relative to the atmosphere. We report here measurements of alkenes, halocarbons, and alkyl nitrates that are typically a factor of 2-10 higher in concentration within the firn air than in the ambient air 1-10 m above the snow. Profiles of concentration to a depth of 2 m into the firn show that maximum values of these trace gases occur between the surface and 60 cm depth. The alkenes show highest pore mixing ratios very close to the surface, with mixing ratios in the order ethene > propene > 1-butene: Mixing ratios of the alkyl iodides and alkyl nitrates peak slightly deeper in the firn, with mixing ratios in order of methyl > ethyl > propyl: These variations are likely consistent with different near-surface photochemical production mechanisms. Diurnal mixing ratio variations within the firn correlate well with actinic flux for all these gases, with a temporal offset between the solar maximum and peak concentrations, lengthening with depth. Using a snow-filled chamber under constant flow conditions, we calculated production rates for the halocarbons and alkenes that ranged between 10 3 -10 5 and 10 6 molecules cm À3 s À1 , respectively. Taken together, these results suggest that photochemistry associated with the surface snowpack environment plays an important role in the oxidative capacity of the local atmospheric boundary layer, and influences post-depositional chemistry, which in turn may affect the interpretation of certain aspects of the ice core records collected previously at Summit. r
Reactive trace gases measured in the interstitial air of surface snow at Summit, Greenland
Atmospheric Environment, 2004
Concentration measurements of nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrous acid (HONO), nitric acid (HNO 3 ), formaldehyde (HCHO), hydrogen peroxide (H 2 O 2 ), formic acid (HCOOH) and acetic acid (CH 3 COOH) were performed in air filtered through the pore spaces of the surface snowpack (firn air) at Summit, Greenland, in summer 2000. In general, firn air concentrations of NO, NO 2 , HONO, HCHO, HCOOH, and CH 3 COOH were enhanced compared to concentrations in the atmospheric boundary layer above the snow. Only HNO 3 and H 2 O 2 normally exhibited lower concentrations in the firn air. In most cases differences were highest during the day and lowest during nighttime hours. Shading experiments showed a good agreement with a photochemical NO x source in the surface snow. Patterns of H 2 O 2 , CH 3 COOH, and HNO 3 observed within the surface snow-firn air system imply that the number of molecules in the snow greatly exceeded that in the firn air. Deduced partitioning indicates that the largest fractions of the acids were present at the ice grain-air interface. In all cases, the number of molecules located at the interface was significantly higher than the amount in the firn air. Therefore, snow surface area and surface coverage are important parameters, which must be considered for the interpretation of firn air concentrations. r