Heterogeneous glyoxal oxidation: a potential source of secondary organic aerosol.

Laboratory studies are described that suggest reactive uptake of glyoxal on particulate containing HNO(3) could contribute to the formation of secondary organic aerosol (SOA) in the upper troposphere (UT). Using a Knudsen cell flow reactor, glyoxal is observed to react on supercooled H(2)O/HNO(3) surfaces to form condensed-phase glyoxylic acid. This product was verified by derivatization and GC-MS analysis. The reactive uptake coefficient, γ, of glyoxal varies only slightly with the pressure of nitric acid, from γ = 0.5 to 3.0 × 10(-3) for nitric acid pressures between 10(-8) and 10(-6) Torr. The data do not show any dependence on temperature (181-201 K) or pressure of glyoxal (10(-7) to 10(-5) Torr). Using the determined reactive uptake kinetics in a simple model shows that glyoxal uptake to supercooled H(2)O/HNO(3) may account for 4-53% of the total organic mass fraction of aerosol in the UT.

Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds.

In situ measurements of the relative humidity with respect to ice (RHi) and of nitric acid (HNO3) were made in both natural and contrail cirrus clouds in the upper troposphere. At temperatures lower than 202 kelvin, RHi values show a sharp increase to average values of over 130% in both cloud types. These enhanced RHi values are attributed to the presence of a new class of HNO3-containing ice particles (Delta-ice). We propose that surface HNO3 molecules prevent the ice/vapor system from reaching equilibrium by a mechanism similar to that of freezing point depression by antifreeze proteins. Delta-ice represents a new link between global climate and natural and anthropogenic nitrogen oxide emissions. Including Delta-ice in climate models will alter simulated cirrus properties and the distribution of upper tropospheric water vapor.

Studies of polar stratospheric cloud formation.

Stratospheric ozone depletion was first reported in 1985. Early on, researchers identified polar stratospheric clouds (PSCs) as being important in chemistry related to ozone depletion. PSCs exist as crystalline water-ice particles (type II), and as crystalline (type Ia) or liquid (type Ib) particles stable above the water-ice frost point. Uncertainty remains concerning the composition and formation mechanism of the most common PSC, type Ia. Here, we consider likely formation mechanisms for type Ia PSCs.

Temperature-dependent optical constants of water ice in the near infrared: new results and critical review of the available measurements.

The optical constants of water ice have been determined in the near infrared from 4000 to 7000 cm(-1). Polycrystalline ice films with thickness as great as ~1164 mum were formed by condensation of water vapor on a cold silicon substrate at temperatures of 166, 176, 186, and 196 K. The transmission of light through the ice films was measured during their growth from 0 to 1164 mum over the frequency range of approximately 500-7000 cm(-1). The optical constants were extracted by means of simultaneously fitting the calculated transmission spectra of films of varying thickness to their respective measured transmission spectra with an iterative Kramers-Kronig technique. Equations are presented to account for reflection losses at the interfaces when the sample is held in a cell. These equations are used to reanalyze the transmission spectrum of water ice (358-mum sample at 247 K) recorded by Ockman in 1957 [Philos. Mag. Suppl. 7, 199 (1958)]. Our imaginary indices for water ice are compared with those of Gosse et al. [Appl. Opt. 34, 6582 (1995)], Kou et al. [Appl. Opt. 32, 3531 (1993)], Grundy and Schmitt [J. Geophys. Res. 103, 25809 (1998)], and Warren [Appl. Opt. 23, 1206 (1984)], and with the new indices from Ockman's spectrum. The temperature dependence in the imaginary index of refraction observed by us between 166 and 196 K and that between our data at 196 K and the data of Gosse et al. at 250 K are compared with that predicted by the model of Grundy and Schmitt. On the basis of this comparison a linear interpolation of the imaginary indices of refraction between 196 and 250 K is proposed. We believe that the accuracy of this interpolation is better than 20%.

Chemistry and microphysics of polar stratospheric clouds and cirrus clouds.

Ice particles found within polar stratospheric clouds (PSCs) and upper tropospheric cirrus clouds can dramatically impact the chemistry and climate of the Earth's atmosphere. The formation of PSCs and the subsequent chemical reactions that occur on their surfaces are key components of the massive ozone hole observed each spring over Antarctica. Cirrus clouds also provide surfaces for heterogeneous reactions and significantly modify the Earth's climate by changing the visible and infrared radiation fluxes. Although the role of ice particles in climate and chemistry is well recognized, the exact mechanisms of cloud formation are still unknown, and thus it is difficult to predict how anthropogenic activities will change cloud abundances in the future. This article focuses on the nucleation, chemistry, and microphysical properties of ice particles composing PSCs and cirrus clouds. A general overview of the current state of research is presented along with some unresolved issues facing scientists in the future.

Antarctic Ozone Depletion Chemistry: Reactions of N2O5 with H2O and HCl on Ice Surfaces.

The reactions of dinitrogen pentoxide (N(2)O(5)) with H(2)O and hydrochloric acid (HCl) were studied on ice surfaces in a Knudsen cell flow reactor. The N(2)O(5) reacted on ice at 185 K to form condensed-phase nitric acid (HNO(3)). This reaction may provide a sink for odd nitrogen (NO(x)) during the polar winter, a requirement in nearly all models of Antarctic ozone depletion. A lower limit to the sticking coefficient, gamma, for N(2)O(5) on ice is 1 x 10(-3). Moreover, N(2)O(5) reacted on HCl-ice surfaces at 185 K, with gamma greater than 3 x 10(-3). This reaction, which produced gaseous nitryl chloride (ClNO(2)) and condensed-phase HNO(3), proceeded until all of the HCl within the ice was depleted. The ClNO(2), which did not react or condense on ice at 185 K, can be readily photolyzed in the Antarctic spring to form atomic chlorine for catalytic ozone destruction cycles. The other photolysis product, gaseous nitrogen dioxide (NO(2)), may be important in the partitioning of NO(x) between gaseous and condensed phases in the Antarctic winter.

Reaction of chlorine nitrate with hydrogen chloride and water at antarctic stratospheric temperatures.

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO(2)) with H(2)0 and hydrogen chloride (HCl) on surfaces that simulate polar stratospheric clouds [ice and nitric acid (HNO(3))-ice and sulfuric acid] are studied at temperatures relevant to the Antarctic stratosphere. The reaction of ClONO(2) on ice and certain mixtures of HNO(3) and ice proceeded readily. The sticking coefficient of ClONO(2) on ice of 0.009 +/- 0.002 was observed. A reaction produced gas-phase hypochlorous acid (HOCl) and condensed-phase HNO(3); HOC1 underwent a secondary reaction on ice producing dichlorine monoxide (Cl(2)O). In addition to the reaction with H(2)0, ClONO(2) reacted with HCl on ice to form gas-phase chlorine (Cl(2)) and condensed-phase HNO(3.) Essentially all of the HCl in the bulk of the ice can react with ClONO(2) on the ice surface. The gaseous products of the above reactions, HOCl, Cl(2)0, and Cl(2), could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the formation of condensed-phase HNO(3) could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.

An epidemiologic study of risk factors associated with pregnancy following female sterilization.

Data on 14,700 female sterilization patients were collected by the International Fertility Research Program (IFRP) from 1972 to 1978 and analyzed to determine risk factors associated with the incidence of pregnancy following sterilization. With a case-control approach, it was found that younger patients (less than or equal to 34 years old) and those who did not lactate after sterilization had a higher risk of becoming pregnant. Patients who were sterilized in the early phases of a service program had a higher risk of pregnancy than those sterilized later. In the laparoscopic series, the relative risk of pregnancy was four times greater in patients who had the prototype spring clip than in patients who had the Falope ring. The relative risk increased to 7.0 when patients who had the prototype spring clip were compared to those who had the Falope ring, electrocoagulation, or the Rocket clip. Patients sterilized by electrocoagulation had a low pregnancy risk, but the risk of an ectopic pregnancy was significantly higher than for those sterilized with mechanical devices. In the culdoscopic series, the tantalum clip had an unacceptable pregnancy risk.

PIP: The International Fertility Research Program (IFRP) collected and analyzed data on 14,700 female sterilization patients from 1972-1978 to determine risk factors associated with the incidence of pregnancy following sterilization. It was found that younger patients (less than 34 years old) and those who did not lactate after sterilization had a higher risk of becombing pregnant. Using a case-control approach it was learned that patients who were sterilized in the early phases of a service program had a higher risk of pregnancy than those sterilized later. The relative risk of pregnancy was 4 times greater in the patients who had the prototype spring clip than in patients who had the Falope ring in the laparoscopic series. When patients who had the prototype spring clip were compared to those who had the Falope ring, the Rocket clip, or electrocoagulation the relative risk increased to 7. Patients sterilized by electrocoagulation had a low pregnancy risk, but the risk of an ectopic pregnancy was significantly higher than for those sterilized with mechanical devices. The tantalum clip had an unacceptable pregnancy risk in the culdoscopic series.