Millimeter wave spectroscopic measurements over the South Pole: 3. The behavior of stratospheric nitric acid through polar fall, winter, and spring

Abstract

Abstract. We present data from a 9-month series of ground-based measurements of stratospheric nitric acid, made over the South Pole from mid-April 1993 to mid-January 1994. Observations were typically made at 3-to 6-day intervals. Both profiles and column densities have been retrieved from pressure-broadened millimeter-wave emission spectra. These measurements provide the first quasi-continuous series of vertical mixing ratio profiles for this species in the heart of the south polar votex. Conversion of NOz to nitric acid by heterogeneous reactions, and its incorporation into polar stratospheric cloud (PSC) particles, along with subsequent gravitational settling, is considered to be the main denitrifying mechanism in the Antarctic stratosphere, setting up conditions for ozone destruction at the end of winter. In our observations, a small increase in HNO3 was seen between April and the end of May, after which a rapid loss took place below 25 km. Column density above ~15 km decreased to _<1/4 its maximum within 30 days, and depletion continued until middle to late July, by which time the nitric acid column above 15 km had diminished by more than a factor of 10. The initial depletion was coincident with the onset of a rapid increase in lidar backscatter from polar stratospheric cloud formation at the same altitude range. Gas-phase depletion was tracked as a function of altitude and temperature and found to be consistent with the temperature and partial pressure relationship for formation of ternary mixtures of HNOa, H2SO4, and H20. Depletion occurred •3 weeks earlier in 1993 than was seen in 1992 column density measurements by Van Allen et al. [1995]. In late June a new layer of HNO3 was generated in the vicinity of 40-km altitude and, subsequently, appeared to be carried downward with general vertical transport of air within the vortex. In spring, as temperatures increased, no rapid increase of gas-phase HNO3 was seen, indicating that gravitational settling had carried PSC-accreted nitric acid to low altitudes. By the end of observations in January 1994, mixing ratios and column densities above •15 km had not yet reached more than about half the values seen the previous April, indicating that a rather large increase in stratospheric HNO3 occurs in the early austral fall over the south polar region.

The Stratospheric and Mesospheric NOy in the 2002–2004 Polar Winters as measured by MIPAS/ENVISAT

“…Reproduced by permission of American Geophysical Union. found to be produced by chemical reactions involving water ion clusters and N 2 O 5 formed from NO x (de Zafra et al, 1997): N 2 O 5 + H 2 O (ion clusters) → 2 HNO 3 . Stiller et al (2005) have shown the consistency between the measured NO x , N 2 O 5 , and HNO 3 fields, and have demonstrated that the large HNO 3 enhancement is caused by the strong downward transport of NO x in this winter (see Figure 1, middle panel).…”

Evolution of the NOy‐N2O correlation in the Antarctic stratosphere during 1993 and 1995

“…The NO y estimates presented here cover the period from October to December (i.e., austral spring‐summer), 1993, and the entire year 1995. They are derived from measurements of HNO 3 , by a ground‐based millimeter‐wave spectrometer (GBMS) [ de Zafra et al , 1997; McDonald et al , 2000; Muscari et al , 2002] operating during 1993 and 1995 from the Amundsen‐Scott base located at the South Pole (90°S); NO and NO 2 by the Halogen Occultation Experiment (HALOE; data version 19) aboard UARS [ Russell et al , 1993]; NO 2 by the Polar Ozone and Aerosol Measurement II instrument (POAM II; data version 6) aboard the French SPOT‐3 polar‐orbiting satellite [ Glaccum et al , 1996]; and calculations of minor NO y constituents such as N 2 O 5 , ClONO 2 , and HO 2 NO 2 from a photochemical box model derived from the SUNY‐SPb 2‐D model [ Smyshlyaev et al , 1998].…”

“…The overall uncertainty in retrieved GBMS HNO 3 measurements (including both systematic and random errors) varies with altitude and time and is bounded approximately between 16% and 22% [ de Zafra et al , 1997]. Total relative errors for HALOE NO and NO 2 in the altitude range 18–30 km are dominated by systematic uncertainties and decrease monotonically with altitude, ranging 15–50% for NO and 7–45% for NO 2 [ Gordley et al , 1996].…”

Ground-based stratospheric O&lt;sub&gt;3&lt;/sub&gt; and HNO&lt;sub&gt;3&lt;/sub&gt; measurements at Thule, Greenland: an intercomparison with Aura MLS observations

“…Starting in 1993, observations of stratospheric O 3 and HNO 3 have been carried out by means of a Ground-Based Millimeter-wave Spectrometer (GBMS) at different sites in both hemispheres, at polar and mid-latitudes (e.g., de Zafra et al, 1997;Muscari et al, 2007;Santee et al, 2007). GBMS data have contributed to shed light on processes related to the global ozone decline and to the dramatic ozone loss occurring over the Antarctic continent every spring.…”

“…GBMS data have contributed to shed light on processes related to the global ozone decline and to the dramatic ozone loss occurring over the Antarctic continent every spring. In particular, in 1993 the GBMS provided the first quasi-continuous yearlong data record of HNO 3 and O 3 vertical profiles in the heart of the south polar vortex showing the direct link between the appearance of PSCs and the rapid removal of HNO 3 from the lower stratosphere (de Zafra et al, 1997). Since then, a continuous monitoring of the stratospheric composition changes in response to the anthropogenic forcing (including ozone depleting substances release) has been carried out by the Network for the Detection of Stratospheric Change (NDSC), now Network for the Detection of Atmospheric Composition Change (NDACC).…”