Detection of reactive nitrogen containing particles in the tropopause region – evidence for a tropical nitric acid trihydrate (NAT) belt (original) (raw)
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The observation of nitric acid-containing particles in the tropical lower stratosphere
Atmospheric Chemistry and Physics, 2006
Airborne in situ measurements over the eastern Pacific Ocean in January 2004 have revealed a new category of nitric acid (HNO 3 )-containing particles in the tropical lower stratosphere. These particles are most likely composed of nitric acid trihydrate (NAT). They were intermittently observed in a narrow layer above the tropopause (18±0.1 km) and over a broad geographic extent (>1100 km). In contrast to the background liquid sulfate aerosol, these particles are solid, much larger (1.7-4.7 µm vs. 0.1 µm in diameter), and significantly less abundant (<10 −4 cm −3 vs. 10 cm −3 ). Microphysical trajectory models suggest that the NAT particles grow over a 6-14 day period in supersaturated air that remains close to the tropical tropopause and might be a common feature in the tropics. The small number density of these particles implies a highly selective or slow nucleation process. Understanding the formation of solid NAT particles in the tropics could improve our understanding of stratospheric nucleation processes and, therefore, dehydration and denitrification.
Atmospheric Chemistry and Physics, 2005
A PSC was detected on 6 February 2003 in the Arctic stratosphere by in-situ measurements onboard the high-altitude research aircraft Geophysica. Low number densities (∼10 −4 cm −3 ) of small nitric acid (HNO 3 ) containing particles (d<6 µm) were observed at altitudes between 18 and 20 km. Provided the temperatures remain below the NAT equilibrium temperature T NAT , these NAT particles have the potential to grow further and to remove HNO 3 from the stratosphere, thereby enhancing polar ozone loss. Interestingly, the NAT particles formed in less than a day at temperatures just slightly below T NAT (T >T NAT −3.1 K). This unique measurement of PSC formation at extremely low NAT saturation ratios (S NAT 10) constrains current NAT nucleation theories. We suggest, that the NAT particles have formed heterogeneously, but for certain not on ice. Conversely, meteoritic particles may be favorable candidates for triggering NAT nucleation at the observed low number densities.
Nitric Acid Trihydrate (NAT) in Polar Stratospheric Clouds
Science, 2000
A comprehensive investigation of polar stratospheric clouds was performed on 25 January 2000 with instruments onboard a balloon gondola flown from Kiruna, Sweden. Cloud layers were repeatedly encountered at altitudes between 20 and 24 kilometers over a wide range of atmospheric temperatures (185 t o 197 kelvin). Particle composition analysis showed that a large fraction of the cloud layers was composed of nitric acid trihydrate (NAT) particles, containing water and nitric acid at a molar ratio of 3 : l ;this confirmed that these longsought solid crystals exist well above ice formation temperatures. The presence of NAT particles enhances the potential for chlorine activation with subsequent ozone destruction in polar regions, particularly in early and late winter.
Atmospheric Chemistry and Physics, 2011
New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different d p50 (50 % lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 Geophysica in the altitude range of 12.0-20.5 km and on board the DLR Falcon-20 at up to 11.5 km altitude. On board the NASA WB-57F size distributions were measured over Central America in the 4 to 1000 nm diameter range with a system of nucleation mode aerosol spec-Correspondence to: R. Weigel (weigelr@uni-mainz.de) R. Weigel et al.: The role of clouds and the nucleation mechanism 2006, at 12.5 km altitude) in cloud free air, above thin cirrus, particularly high N NM were observed. Recent lifting had influenced the probed air masses, and N NM reached up to 16 000 particles cm −3 (ambient concentration). A sensitivity study using an aerosol model, which includes neutral and ion induced nucleation processes, simulates N NM in reasonable agreement with the in situ observations of clear-air NPF. Based on new, stringent multi-CPC criteria, our measurements corroborate the hypothesis that the tropical UT and the TTL are regions supplying freshly nucleated particles. Our findings narrow the altitude of the main source region to the bottom TTL, i.e. to the level of main tropical convection outflow, and, by means of measurements of carbon monoxide, they indicate the importance of anthropogenic emissions in NPF. After growth and/or coalescence the nucleation mode particles may act as cloud condensation nuclei in the tropical UT, or, upon ascent into the stratosphere, contribute to maintain the stratospheric background aerosol.
Journal of Geophysical Research, 1998
Extensive measurements of gaseous nitric acid (HNO3) have been performed in the upper troposphere and lower stratosphere using aircraft-based ion-molecule reaction mass spectrometry (IMRMS). The measurements, which took place in summer and winter between November 1994 and July 1996, cover latitudes between 29øN and 57øN and altitudes between 5.5 and 13 km. According to meteorological analyses, potential vorticity values up to 9.5 PVU (1 PVU = 10 -6 m 2 s -• K kg -•) were reached. Stratospheric HNO3 mixing ratios ranged between 300 and 2200 parts per trillion by volume (pptv). In the upper troposphere, nitric acid mixing ratios ranged between 100 and 2000 pptv, with the largest values influenced by fast vertical transport from the planetary boundary layer. These values exceed previous measurements and model calculations. The relatively high upper tropospheric nitric acid mixing ratio indicates a large rate for NOx recycling from gaseous nitric acid, and possibly also an increased efficiency of aerosol activation, which may lead to an increased albedo of cirrus clouds.
Journal of Geophysical Research, 1997
This paper presents an analysis of odd nitrogen partitioning determined from instruments aboard the Upper Atmosphere Research Satellite (UARS). The UARS data set provides the first global maps and the best temporal coverage to date of NO•/NO•. Our analysis spans latitudes from 60øS to 60øN and altitudes between 22 and 35 km for three separate, month-long periods between August 1992 and March 1993. These periods are characterized by substantial stratospheric aerosol loading as a result of the eruption of Mount Pinatubo in June 1991. Active odd nitrogen (NOr) is estimated from sunset measurements of NO and NO2 made by the halogen occultation experiment (HALOE). Total odd nitrogen (NON) is the sum of NO• and correlated nighttime measurements of C1ONO2 and HN03 made by the cryogenic limb array etaion spectrometer (CLAES). Typical values of UAP•S NO•/NO v during our study periods are 0.85 at 1000 K (35 km), 0.60 at 800 K (31 km), 0.25 at 650 K (26 km), and 0.10 at 550 K (22 km). Significant latitudinal gradients in nitrogen partitioning are observed in the winter hemisphere at altitudes below 1000 K, with the highest values of NO•/NOy found at midlatitudes. Comparison of the UARS NO•/NOy with predictions from a constrained version of the Goddard two-dimensional fixed circulation model of stratospheric photochemistry demonstrates generally good agreement at the altitudes and latitudes studied. The model estimates have a slightly low bias that diminishes •s the aerosol loading decreases between August 1992 and March 1993. At lower altitudes under high aerosol loading, the model does not predict the winter hemispheric, subtropical gradients of NO•/NOy seen in the UARS d•t•. This discrepancy may be due to the lack of similar gradients in the ozone and surface area density fields which constrain the model. and destroys ozone through the catalytic cycle NO+O3 -. NO2+O2 (2) NO2 + O --* NO + 02 NET ß Oa + O -. 202 In the middle to upper stratosphere, these NOs reactions account for a substantial fraction of total ozone , r a•-/"•1 _ _ I AAA1 r-D_._l A.-I.-I •'4-..... ;,. fined as NO u -NO•+NOa+HNOa+C1ONO2+2xN20, (3) and includes both active (NOs) and reservoir (I-INOa and C1ONO2) species (other species not included in (3), such as HO2NO2, make up only ,,,1-2% of NO u and are ignored in this paper). The reservoir species do not destroy ozone. Data from the Upper Atmosphere Research Satellite (UARS), launched September 1991, allow an unprecedented examination of nitrogen partitioning as a function of latitude, altitude, and aerosol loading. Of the previous measurements, only the limb infrared monitor of the stratosphere (LIMS) provided a global picture of stratospheric nitrogen. The LIMS NO v mea-8955 8956 MORRIS ET AL.: NITROGEN PARTITIONING AS OBSERVED BY UARS surements, however, were limited to NO2 and HNOa ET AL.' NITROGEN PARTITIONING AS OBSERVED BY UARS 8959 PARTITIONING AS OBSERVED BY UARS 8965
Nitric acid trihydrate nucleation and denitrification in the Arctic stratosphere
Atmospheric Chemistry and Physics, 2014
Nitric acid trihydrate (NAT) particles in the polar stratosphere have been shown to be responsible for vertical redistribution of reactive nitrogen (NO y ). Recent observations by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the CALIPSO satellite have been explained in terms of heterogeneous nucleation of NAT on foreign nuclei, revealing this to be an important formation pathway for the NAT particles. In state of the art global-or regional-scale models, heterogeneous NAT nucleation is currently simulated in a very coarse manner using a constant, saturation-independent nucleation rate. Here we present first simulations for the Arctic winter 2009/2010 applying a new saturation-dependent parametrisation of heterogeneous NAT nucleation rates within the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulation shows good agreement of chemical trace species with in situ and remote sensing observations. The simulated polar stratospheric cloud (PSC) optical properties agree much better with CALIOP observations than those simulated with a constant nucleation rate model. A comparison of the simulated particle size distributions with observations made using the Forward Scattering Spectrometer Probe (FSSP) aboard the high altitude research aircraft Geophysica, shows that the model reproduces the observed size distribution, except for the very largest particles above 15 µm diameter. The vertical NO y redistribution caused by the sedimentation of the NAT particles, in particular the denitrification and nitrification signals observed by the ACE-FTS satellite instrument and the in situ SIOUX instrument aboard the Geophysica, are reproduced by the improved model, and a small improvement with respect to the constant nucleation rate model is found.
Journal of Geophysical Research, 1997
Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + C1ONO2 + 2N20 5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO 2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NOy reservoir are well understood in the lower stratosphere. Introduction Stratospheric ozone (03) is destroyed in catalytic cycles involving oxides of hydrogen (HO x = OH + HO2), nitrogen (NO x = NO + NO2), chlorine (C10 x = C1 + C10 + 2C1OOC1), and bromine (BrO x = Br + BrO). Our understanding of 03 destruction cycles changed significantly with the recognition of the role of heterogeneous reactions in the stratosphere
Geophysical Research Letters, 1990
Total reactive nitrogen (NOv) between 15 and 29 km was measured for the first time on board a balloon within the Arctic cold vortex. Observations of HN03, aerosol, and ozone were made by instruments on the same balloon gondola which was launched from Esrange, Sweden (68øN, 20øE) on January 23, 1989. The blO• mixing ratio was observed to increase very rapidly from 6 ppbv at 18 km altitude to a maximum of 21 ppbv at 21 km, forming a sharp layer with a thickness of about 2 kin. A minimum in the NO v mixing ratio of 5 ppbv was found at 27 km. The measured HNO3 profile shows broad similarities to that of NO v . This observation, together with the observed very low column amount of NO2, shows that NOs had been almost totally converted to HNO3, and that NO v was composed mainly of HNO3. The enhanced aerosol concentration between 19 and 22 km suggests that the maximum abundance of HNO3 trapped in the form of nitric acid trihydrate (NAT) was about 6 ppbv at 21 km. The sampled air parcels were highly supersaturated with respect to NAT. Although extensive denitrification throughout the stratosphere did not prevail, an indication of denitrification was found at altitudes of 27 and 22 kin, and between 18 and 15 km. + aerosol nitrate, plays an important role in the chemistry of the winter polar stratosphere. HNO3, in combination with H20, forms aerosols composed of nitric acid trihydrate (NAT) at temperatures higher than that required for water ice particle formation. These aerosols can provide sites for heterogeneous reactions, one of which converts HC1 and chlorine nitrate (C1ONO2, a temporaw reservoir of CIO) into reactive chlorine molecules and HNO.• [e.g. Solomon et ai., 1986; McElroy eta!., 19861. In 437