Tropospheric Environment Research Articles

Photochemistry of Imidazole-2-carbaldehyde in Droplets as a Potential Source of H2O2 and Its Oxidation of SO2.

Hydrogen peroxide (H2O2) plays a crucial role as an oxidizing agent within the tropospheric environment, making a substantial contribution to sulfate formation in hydrated aerosols and cloud and fog droplets. Field observations show that high levels of H2O2 are often observed in heavy haze events and polluted air. However, the source of H2O2 remains unclear. Here, using the droplets formed in situ by the deliquescence of hygroscopic compounds under a high relative humidity (RH), the formation of H2O2 by the photochemistry of imidazole-2-carbaldehyde (2-IC) under ultraviolet irradiation was explored. The results indicate that 2-IC produces IM-C•-OH and IM-C•═O radicals via H transfer itself to its excited triplet state and generates H2O2 and organic peroxides in the presence of O2, which has an evident oxidizing effect on SO2, suggesting the potential involvement of this pathway in the formation of atmospheric sulfate. H2O2 formation is limited in acidic droplets or droplets containing ammonium ions, and no H2O2 is detected in droplets containing nitrate, whereas droplets containing citric acid have an obvious promotion effect on H2O2 formation. These findings provide valuable insights into the behaviors of atmospheric photosensitizers, the source of H2O2, and the formation of sulfate in atmospheric droplets.

Effects of tropospheric ozone on groundnut (Arachis hypogea L.) cultivars: Role of plant age and antioxidative potential

Ozone (O3) is a secondary atmospheric pollutant present in the tropospheric environment. Ozone enters in internal tissue of leaf through stomata and produces reactive oxygen species (ROS) which damages cellular membrane, alter gene expression and metabolic activities and ultimately caused death of the plant tissues. Certain defensive mechanism occurs in the internal part of leaves to eliminate generated ROS. However, there is significant change in the levels and kind of defence traits as plants develop from the seedling to juvenile to mature and senescent stages. A field study was conducted for two consecutive seasons with five cultivars of groundnut (Arachis hypogea L cv. TG-37A, TPG-41, TAG-24, GG-20, and Dh-86) to assess the intra-specific variation in defensive response against ozone at various plant developmental stage. Results of the study showed that ozone significantly affected biomass and primary metabolites, generate ROS and increases membrane permeability in all the groundnut cultivars. In response to ROS, groundnut cultivars produced non-enzymatic and enzymatic antioxidants. Study found that the severity of the effect varied among the cultivars and by developmental stages. Cultivar Dh-86 showed higher antioxidative activity and least biomass sensitivity to ozone. Although accumulation of non-enzymatic antioxidants was present to provided defence against ozone, activity of enzymatic antioxidants varied at different growth stages and corresponds to the biomass sensitivity. Study concluded that the ozone phytotoxicity is dependent on the antioxidative potential of the cultivars and the growth stage of the plant. Further, the activity of APX played a measure role for age dependent plant sensitivity in groundnut.

A Feasibility Analysis of Collaborative Mission Using Mars Airplane and Mars Balloon - Mars Aerial-Exploration for Terrestrial and Tropospheric Environment Observation -

A Feasibility Analysis of Collaborative Mission Using Mars Airplane and Mars Balloon - Mars Aerial-Exploration for Terrestrial and Tropospheric Environment Observation -

Forced gravity waves and the tropospheric response to convection

We present theoretical work directed toward improving our understanding of the mesoscale influence of deep convection on its tropospheric environment through forced gravity waves. From the linear, hydrostatic, non‐rotating, incompressible equations, we find a two‐dimensional analytical solution to prescribed heating in a stratified atmosphere, which is upwardly radiating from the troposphere when the domain lid is sufficiently high. We interrogate the spatial and temporal sensitivity of both the vertical velocity and potential temperature to different heating functions, considering both the near‐field and remote responses to steady and pulsed heating. We find that the mesoscale tropospheric response to convection is significantly dependent on the upward radiation characteristics of the gravity waves, which are in turn dependent upon the temporal and spatial structure of the source, and the assumed stratification. We find a 50% reduction in tropospherically averaged vertical velocity when moving from a trapped (i.e. low lid) to upwardly radiating (i.e. high lid) solution but, even with maximal upward radiation, we still observe significant tropospheric vertical velocities in the far‐field 4 h after heating ends. We quantify the errors associated with coarsening a 10 km‐wide heating to a 100 km grid (in the way a general circulation model (GCM) would), observing a 20% reduction in vertical velocity. The implications of these results for the parametrization of convection in low‐resolution numerical models are quantified, and it is shown that the smoothing of heating over a grid box leads to significant in‐grid‐box tendencies, due to the erroneous rate of transfer of compensating subsidence to neighbouring regions. Further, we explore a simple time‐dependent heating parametrization that minimizes error in a parent GCM grid box, albeit at the expense of increased error in the neighbourhood.

Anthracene and phenanthrene tropospheric oxidation promoted by the nitrate radical in the gas-phase. Theoretical modelistic study

Polycyclic aromatic hydrocarbons and their oxidized derivatives are ubiquitous environmental pollutants that are toxic to different degrees. The NO3 radical is known to be an important actor in fostering nighttime atmospheric chemistry; hence it could elicit some nocturnal PAH-loss processes. In this study the gas phase pathways open to the initial anthracene and phenanthrene NO3 π−radical adducts in the presence of O2, NO and NO2 are examined by Density Functional Theory to ascertain the mechanistic features of their NO3-initiated oxidative degradation. Unimolecular steps involving the initial adducts (ring closures or fragmentation) present rather high free energy barriers and seem unlikely. Regarding bimolecular reactions, any radical present in the tropospheric environment can give an intrinsically fast radical coupling with the initial adducts, thus producing bifunctional closed shell species. The addition of ground state dioxygen is a relatively fast step that is reversible in some cases, less so in others. It entails subsequent reaction steps, which involve the peroxyl radical intermediate and addition and loss of small species as NO, NO3, NO2 and O2. These steps can either trigger a β−fragmentation with formation of a closed shell dialdehyde or formation of a closed shell nitroxy ketone, bifunctional species that appear to be the most likely products when typical tropospheric concentrations are taken into account.

A Simple Two-Dimensional Ray-Tracing Visual Tool in the Complex Tropospheric Environment

This paper introduces a simple two-dimensional ray-tracing visual tool, Ray-VT, for simulating propagations in the tropospheric environment. It is capable of tracing ray paths through range-dependent refractive conditions as well as arbitrary terrain cases. The fundamental computations are based on the piece-wise application of Snell’s law including a small angle approximation. The Ray-VT can be used to investigate the effects of ducting propagations and to assess the performances of radar systems. It can also be used as an educational aid for understanding the propagation characteristics in complex environments.

An Examination of the Thermodynamic Impacts of Western North Pacific Tropical Cyclones on Their Tropical Tropospheric Environment

Abstract The present study examines the tropospheric thermodynamic anomalies induced by western North Pacific tropical cyclone (TC) passage using storm-relative composites. Negative moist static energy (MSE) anomalies containing embedded westward-propagating anomalies generally occur only following larger TCs for two months following TC passage in a region extending from the domain center to ~3000 km to its west. Larger TCs force negative MSE anomalies likely because of feedbacks from stronger, broader TC-induced negative sea surface temperature (SST) anomalies and the excitation of TC-induced Rossby waves to the southeast of the TC. The negative MSE anomalies are composed of lower- and midtropospheric negative latent energy anomalies with smaller contributions from boundary layer and upper-tropospheric negative sensible heat anomalies. The lower- and midtropospheric negative MSE anomalies are forced by the TC, whereas the upper-tropospheric negative MSE anomalies are forced by the Madden–Julian oscillation. Vertically integrated MSE budgets at the domain center reveal negative MSE tendencies that are primarily forced by surface latent heat flux anomalies resulting from the TC-induced negative SST anomalies. Smaller negative MSE tendencies are due to 1) zonal and meridional advection of MSE anomalies by the Rossby waves and 2) enhanced top-of-the-atmosphere longwave radiative flux anomalies potentially associated with a reduction in the greenhouse gas effect of water vapor. The budget analysis in the west region is generally similar except that all terms are comparable in magnitude and relatively weaker. These results conservatively suggest that larger TCs can anomalously cool and dry their synoptic-scale environment for ~40 days following TC passage.

Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities

The present paper describes background, mission, research topics, and preliminary results of the research project “Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)”. TOMACS is one of the research projects of “Social System Reformation Program for Adaption to Climate Change” which has been started since July 2010 under the “Special Coordination Funds for Promoting Science and Technology” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). TOMACS aims to understand the processes and mechanisms of extreme weather, using dense meteorological observation networks designed in the Tokyo metropolitan district, to develop a monitoring and predicting system of extreme phenomena (MPSEP), and to implement social experiments on extreme weather resilient cities in collaboration with related government institutions, local governments, private companies, and residents. More than 25 organizations and over 100 people participate in the present research projects. One of unique features of TOMACS is utilization of dense meteorological instruments in the Tokyo Metropolitan area which is one of the most urbanized areas in the world. The field campaign in the Tokyo metropolitan area, using research instruments and operational meteorological networks is planned by MRI and thirteen groups in the summers of 2011-2013 to target the tropospheric environment, boundary layer, initiation of convections and lifecycle of thunderstorms. Observation on environmental conditions of convections are carried out using radio sonde, wind profiler, GPS network, unmanned air viecle, and network of automated weather stations. Generation and development of convective precipitations are investigated by observations using Doppler lidar, rapid scan geostationary satellite, Kuband polarimetric radar, X-band polarimetric radar network (X-NET) and C-band research polarimetric radar and C-band operational Doppler radars. Several thunderstorms were captured by the dense meteorological network during 2011 campaign observations. The present paper shows preliminary results of the analysis. Social experiments on extreme weather resilient city using radar networks are also presented.

Physical and optical properties of aerosols in a free tropospheric environment: Results from long-term observations over western trans-Himalayas

Simultaneous and collocated estimates of near-surface mass concentration of black carbon (BC), number size distribution (NSD) and total number concentration (NT) of composite aerosols, columnar spectral aerosol optical depth (AOD) and local meteorological parameters were made from Aug 2009 to July 2012 at the high altitude (4520 m amsl), remote location Hanle in western trans-Himalayas. Even though all the aerosol parameters remain quite low, large annual variations are seen in the monthly mean values of BC (25 ng m−3–181 ng m−3), total number concentrations of composite aerosols (628 cm−3–1500 cm−3) and AOD (0.05–0.16). Size segregated correlation analysis reveals that the BC mass contributes significantly to the size range of 200–400 nm of the submicron aerosol size spectra. The diurnal variation of BC mostly has been dampened; yet seems to be prominent during spring, showing the presence of weak boundary layer dynamics. In contrast, the diurnal fluctuations in total number concentration have been mostly controlled by the new particle formation events, leading to bursts of large concentrations of ultrafine particles, which subsequently undergo coagulation. Spectral dependence of AOD also shows large monthly variations, with the Angstrom exponent varying from ∼0.52 to 1.3, with a mean value of ∼0.95 ± 0.21. The vertical distribution of extinction coefficients, obtained from CALIPSO data, indicates the presence of elevated aerosol layers, attributed mainly to the influence of long range transport of aerosols from the west Asian and Indian desert region.

Fine and ultrafine particles at a near–free tropospheric environment over the high-altitude station Hanle in the Trans-Himalaya: New particle formation and size distribution

[1] Number-size distributions of ultrafine, fine, and accumulation mode aerosols in the size range 5–1300 nm have been measured regularly from the pristine, high-altitude (for 4520 m above mean sea level) station Hanle in the Trans-Himalaya during the summer and autumn (August–November) 2009. The total number concentration ranged from 80 to 8000 cm−3 with a mean value of 1150 cm−3. Examination of the temporal variations of the size distributions indicated that formation of new ultrafine particles from the precursor gases (probably transported from the valley regions) was highly probable during the forenoon hours of the day, especially during the summer when the insolation was abundant, the process becoming increasingly less efficient as the season progressed toward winter. The time of occurrence of maximum concentration was generally during the forenoon, a few hours after sunrise, and this time shifted to later parts of the day as the season progressed toward winter, probably associated with later sunrise and low solar elevations. The number-size distributions revealed two prominent modes: a nucleation mode with mode diameter at ∼16 nm and a consistent accumulation mode with the mode diameter ranging between 115 and 150 nm. Examining the temporal features with the air mass types, it was noticed that the number concentration increased, and the accumulation mode broadened when west Asian air mass prevailed. In summer (during August) the number concentrations tended to higher values associated with air mass from the Indian origin. The ratio of the Aitken to accumulation mode concentration indicated that the aerosol particles existing over the site are aged.

Monitoring of sulfur dioxide in the guinea savanna zone of Nigeria: implications of the atmospheric photochemistry

The level of sulfur(IV) oxide (SO2) in the tropospheric environment of Ilorin is presented using three urban classes and a control site from 2003-2006 wet and dry seasons. The mean concentrations over the years during wet and dry seasons were 1.29 ± 0.17 and 7.17 ± 0.87 (ppb), respectively. The wet season concentration was 15.25% lower than the dry season due to rain attenuation. The mean values at the control site for two seasons were one order of magnitude lower than those in the urban sites. The overall average concentration over Ilorin city was 4.23 ± 0.52 ppb. The value is comparable with other cities of the world and is within the limit of the United State Environmental Protection Agency (USEPA) Guidelines for Air Quality Standards. SO2 levels were found to varied significantly with vehicular intensity, other anthropogenic activities also decreased drastically during wet season. There was a significant difference (p = 0.05) between SO2 concentration with high and low traffic flow count; however, there was no difference (p = 0.05) between high traffic/medium population and medium traffic/high population density areas. The regression analysis indicated a correlation between SO2 and the hourly traffic volume in almost all the sites.

Rainfall Types in the West African Sudanian Zone during the Summer Monsoon 2002

Abstract Enhanced surface and upper-air observations from the field campaign of the Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa (IMPETUS) project are used to partition rainfall amounts over the West African Sudanian zone during the 2002 summer monsoon season into several characteristic types and subtypes of precipitating systems. The most prominent rainfall subtype was fast-moving, long-lived, and extensive cloud clusters that often developed far upstream over the central Nigerian highlands in the afternoon hours and arrived at the Upper Ouémé Valley (UOV) after midnight. These organized convective systems (advective OCSs, subtype Ia) accounted for 50% of the total rain amount in the UOV catchment in Benin. Subtypes Ia and IIa (i.e., locally developing OCSs) were found to pass by or organize when a highly sheared environment with deep and dry midtropospheric layers was present over the UOV. These systems were most frequent outside the peak of the monsoon season. The second major type of organized convection, termed mesoscale convective systems (subtypes Ib, IIb, and IIIb) in the present study, contributed 26% to the annual UOV precipitation. They occurred in a less-sheared and moister tropospheric environment mainly around the height of the rainy season. A third distinct class of rainfall events occurred during an unusual synoptic situation in which a cyclonic vortex to the north of the UOV led to deep westerly flow. During these periods, the African easterly jet was lacking. The so-called vortex-type rainfalls (subtypes IIIa, IIIb, and IIIc) contributed about 9% to the annual rainfall totals.

Contrail Formation and Propulsion Efficiency

The contrail factor is the ratio of water vapor to enthalpy added by combustion to the exhaust plume from an aircraft engine. It is the key parameter determining the highest temperature at which contrails will form behind a particular engine on a particular aircraft. Cycle calculations are used to estimate contrail factors for a range of e ight environments at a range of power settings, for generic low-bypass and high-bypass turbofan gas-turbine engines. It is found that, contrary to assumptions made in current methods of contrail forecasting, the contrail factor is not constant for a given engine type. The contrail factor varies even forthe same engine at different power settings and e ight conditions. Results are shown for a range of conditions, including e ight levels between 25,000 and 50,000 ft in a standard atmosphere, e ight Mach numbers ranging from 0.4 to 0.9, and powersettings from idle (low) to military (high). The computed contrail factors range from 0.030 to 0.053 g¢ kg i 1±± C i 1 for the low-bypass engine and from 0.038 to 0.090 g¢ kg i 1± C i 1 for the high-bypass engine. Changes in contrail factor can be roughly related to changes in the threshold environmental temperature for contrail formation by the relationship that a 10% increase in contrail factor results in a 1 ± C higher threshold temperature in a typical upper tropospheric environment for threshold temperatures near i 50 ±± C. These calculations do not yield precise estimates of contrail factors for specie c engines, but demonstrate that contrail factors for a given engine are generally higher at lower power settings at a given Mach number, higher at higher Mach numbers at a given power setting, and higher at higher altitudes in general.

Extratropical Transformation of Typhoon Vicki (9807): Structural Change and the Role of Upper-tropospheric Disturbances.

Extratropical transformation of Typhoon Vicki (9807) is diagnosed in relation to its environment, particularly with respect to interactions with upper tropospheric disturbances, using the gridded dataset of global analysis (GANAL) produced by the Japan Meteorological Agency. TY Vicki made landfall on Japan with its maximum intensity on 22 September 1998, causing damage with strong winds. Vicki lost the diabatically generated potential vorticity (PV) anomaly at 00UTC 23 September 1998, when it was supposed to complete the extratropical transformation. It still had a considerable diabatic PV anomaly during passage over Japan, which is consistent with the cyclone intensity. At 06UTC 22 September, Vicki was located in the lower-baroclinic zone, and strong horizontal divergence directly above the cyclone center was dissipated in the upper troposphere, which suggest that was already beginning extratropical transformation. Regarding the upper tropospheric environment, Vicki was moving northward to the right entrance of the jet streak, and a trough, i.e., mesoscale PV anomaly, approached to the west of Vicki. To the north of the cyclone, mid-tropospheric warm frontogenesis and the associated northward out-flow were induced. To the west of the cyclone, the upper-tropospheric frontogenesis associated with the jet entrance and the trough contributed to upper-tropospheric outflow from the cyclone and midtropospheric dry-air inflow. These contributed to organizing a wide rainfall region in the northern semicircle of the cyclone and to limiting the rainfall region in the southwest of the cyclone center. It is also suggested that interactions between upper- and mid-tropospheric outflow, and the midlatitude jet streak to the north of the cyclone contributed to a deepened layer of horizontal divergence that delayed the weakening of the cyclone during the start of the extratropical transformation.

Radiative Sensitivity to Water Vapor under All-Sky Conditions

Using the National Center for Atmospheric Research Community Climate Model, version 3, radiation transfer model and a realistic tropospheric environment including the International Satellite Cloud Climatology Project cloud fields, all-sky radiative sensitivity to water vapor is assessed. The analysis improves upon previous clear-sky and model-based studies by using observed clouds, assessing realistic vertically varying perturbations, and considering spatial gradients in sensitivity through the Tropics and subtropics. The linearity of sensitivity is also explored. The dry zones of the subtropics and the eastern Pacific Ocean are found to be particularly sensitive to the water vapor distribution, especially for variations in the upper troposphere. The cloud field is instrumental in determining spatial gradients in sensitivity both at the top of the atmosphere and the surface. Throughout the Tropics, outgoing longwave radiation is most sensitive to water vapor in the upper troposphere, especially when perturbations characteristic of either natural variations or measurement uncertainties are considered. In contrast, surface radiative fluxes are everywhere most sensitive to specific humidity variations in the lower troposphere.

Estimating Chemical Errors in Large-scale Simulations of Aircraft Emissions

Calculations of a relatively comprehensive chemical reaction mechanism applied to individual parcels of aircraft emissions under upper tropospheric conditions show that over a typical residence time of air in the up. per troposphere, each aircraft-emitted NOx molecule produces about 2-3 molecules of O3 per day as long as the reactive NOy remains in the upper troposphere. In the upper tropospheric environment characterized by low ambient turbulence and appreciable vertical wind shear, aircraft plumes grow slowly during initial stages, and take several days to diffuse to a size comparable to the grid volume used by global-scale Eulerian models. By assuming aircraft emissions are immediately diluted into a larger grid cell volume, larger-scale models will overestimate the calculated O3 production by 20 to 30 %. This overestimate depends on the vertical diffusion efficiency, vertical wind shear, and NOx concentrations in the ambient environment. This overestimate can be compensated for in larger scale models by reducing the reaction coefficient of the NO + HO2 reaction by less than 3% under typical upper tropospheric conditions.

Isotopic measurements of stratospheric ozone

Isotope ratios of stratospheric ozone samples collected during four balloon flights are reported. In an altitude range between 22 and 33 km all ratios show enrichments between 7 and 11%, somewhat lower for 49O3 than for 50O3. Those enrichments are in very good agreement with results from laboratory isotope studies when stratospheric pressure and temperatures are included. The new data presented do raise questions about past stratospheric ozone isotope measurements which sometimes showed high values never observed in the laboratory or tropospheric environment.

Ozone: a tool for probing programmed cell death in plants.

Rapid increases in industrialization and other human activities during the twentieth century have contributed significant amounts of toxic gaseous pollutants to the tropospheric environment that pose a significant threat for the survival and productivity of native and cultivated ecosystems (Krupa and Kickert, 1989). Among various pollutants studied to date, the gaseous air pollutant ozone (O3) has caused more damage to both natural and cultivated crop plants in industrialized nations than any other pollutant (Heagle, 1989; Krupa and Kickert, 1989). O3 is produced both in the troposphere and in the stratosphere. Stratospheric O3 is generated through photolysis of molecular oxygen by ultraviolet solar radiation (Chameides et al, 1994). In the troposphere, O3 is produced by oxygen/ozone equilibrium reactions involving NO2/NO and light (Figure 1, reaction 1). In addition, reactions involving the photo-oxidation of carbon monoxide (Figure 1, reaction 2), unburned hydrocarbons such as methane (Figure 1, reaction 3), formaldehyde and other non-methane organic compounds (Figure 1, reaction 4; Fishman et al, 1985) also contribute to tropospheric O3.

OH Field Measurements: A Critical Input into Model Calculations on Atmospheric Chemistry

Abstract As part of a European program, a field campaign was carried out in May 1994 at the Izana Station, Tenerife, Canary Islands, to study the influence of European emissions on the oxidizing capacity of a clean tropospheric environment. This paper contains daytime measurements covering the OH chemistry. The OH measurements are taken with the Multipass Optical Absorption Spectroscopy (MOAS) instrument, which is based on the differential absorption technique. The main parameters controlling the OH concentration were monitored. Calculations from a box model are used to compare its results with the measurements. The comparison shows good agreement in the OH daily variations. The measured OH in absolute terms, however, always has lower values than the calculated ones, indicating that an overall OH sink is missing. This sink term is composed of a continuous background, most probably caused by biogenic emissions and temporal variations from pollutional events superimposed. The photolysis of formaldehyde cont...

Testing the daytime oxidizing capacity of the troposphere: 1994 OH field campaign at the Izaña observatory, Tenerife

A field campaign was carried out during May 1994 at the Izaña station, Tenerife. This campaign was part of the program Environment and Climate sponsored by the European Commission to study the influence of European emissions on the oxidizing capacity of a clean tropospheric environment. Daytime and also nighttime measurements were made, covering the OH as well as the NO3 chemistry. This paper presents the OH measurements taken with a multipass optical absorption spectrometer (MOAS) and discusses the daytime chemistry in a statistical and therefore more preliminary way. All relevant parameters influencing the OH concentration were monitored. From the data the two main contributions to the OH production can clearly be discerned and are given by the primary production following the ozone photolysis and the O(1D)‐H2O reaction and by the catalytic reactions of NOx in the recycling process. The latter processes prove to contribute a dominant part to the OH concentration. The measurements of the nonmethane hydrocarbons (NMHC) especially of the biogenics, indicate a considerable influence of the NMHC on the absolute values of the OH concentration at Tenerife.