Engineering topics

Hameed, S.

Publications and source records attributed to Hameed, S..

At least 19 records

NASA NTRS1985

A model investigation of the impact of increases in anthropogenic NOx emissions between 1967 and 1980 on tropospheric ozone

The impact of anthropogenic NOx emission on tropospheric ozone has been investigated. Two statistical models were used for estimating annual global emissions of NOx and for driving the trend in the emission for the years 1966-1980. Both models show a steady increase in the NOx emission, except for two brief periods of leveling off: after 1973 and after 1978. The impact was estimated by calculating the rates of emissions as functions of latitude, longitude, and year, with a one-dimensional (latitudinal) model, which included coupled tropospheric photochemistry and diffusive meridional transport. Steady-state photochemical calculations with prescribed NOx emissions appropriate for 1966 and 1980 indicate an ozone increase of 8-11 percent in the Northern Hemisphere, a result compatible with the rise in ozone suggested by the observations.

Dignon, J.↗

NASA NTRS1983

A model study of the effects of intermittent loss on odd nitrogen concentrations in the lower troposphere

A time-dependent box model of the lower troposphere which includes a description of photochemical and physical processes has been developed. This model has been applied to the calculation of nitric acid and NO(x)(NO + NO2) concentrations over a diurnal cycle which includes precipitation. Nitric acid concentrations and the HNO3/NO(x) ratio are found to be highly variable under the assumptions regarding the frequency, duration, and intensity of precipitation employed in this model. The chemistry of odd nitrogen compounds during the night is potentially important in establishing the level of nitric acid in the lower troposphere. These calculations also indicate that relatively large errors may occur when the continuity equation describing nitric acid variations is averaged over a diurnal cycle which includes precipitation. Interpretation of simultaneous measurements of HNO3 and NO(x) will require some knowledge of the history of the observed air mass and may require an improved understanding of nighttime odd nitrogen chemistry.

Stewart, R. W.↗

NASA NTRS1983

Latitudinal variation of tropospheric ozone in a photochemical model

A zonally, vertically, and annually averaged numerical model of trace gases in the troposphere is used to examine the variation of ozone as a function of latitude. Processes included in the ozone budget are a source due to downward transport of ozone from the stratosphere, deposition at earth's surface, north-south diffusive transport, and photochemical reactions. Sensitivity of calculated ozone concentrations to the latitude variation and magnitude of the stratospheric source is presented. The model indicates a net photochemical source of ozone in the Northern Hemisphere and a net chemical sink in the tropical latitudes. Calculated variation of ozone concentration with latitude is in qualitative agreement with observations.

Hameed, S.↗

NASA NTRS1983

An analysis of periodicities in the 1470 to 1974 Beijing precipitation record

An analyis of a time series consisting of an annual index of dryness/wetness for the years 1470 to 1974 in Beijing, China is presented. Its power spectrum shows that dominant cycles occur with long periods of the order of 80 years. Cycles with periods of 11 and 22 years are weak or non-existent, but a significant signal at 18.7 years (which is also the period of a component of the lunar tide generating force) is detected. The long term variations in Beijing precipitation appear to lag long term (Gleissberg) variations in solar activity by nearly 75 years. A pattern which spans nearly 150 years in the Beijing record is found to be repeated with notable similarity.

Hameed, S.↗

NASA NTRS1983

Phase coherence of solar cycle minima over two 178-year periods

The phases of solar cycle minima are compared with an 'ideal' sunspot cycle of the mean period of 11.4 years. The observed departures from the ideal model form a pattern over 16 cycles (approximately 178 years) which appears to be repeated over the next 16 cycles. Both in mathematic sign and amplitude the two 178-year cycles are coherent to a statistically significant level of 98 percent. If true, this furnishes a basis for predicting sunspot cycle minima.

Fairbridge, R. W.↗

NASA NTRS1983

A general circulation model study of atmospheric carbon monoxide

The carbon monoxide cycle is studied by incorporating the known and hypothetical sources and sinks in a tracer model that uses the winds generated by a general circulation model. Photochemical production and loss terms, which depend on OH radical concentrations, are calculated in an interactive fashion. The computed global distribution and seasonal variations of CO are compared with observations to obtain constraints on the distribution and magnitude of the sources and sinks of CO, and on the tropospheric abundance of OH. The simplest model that accounts for available observations requires a low latitude plant source of about 1.3 x 10 to the 15th g/yr, in addition to sources from incomplete combustion of fossil fuels and oxidation of methane. The globally averaged OH concentration calculated in the model is 750,000/cu cm. Models that calculate globally averaged OH concentrations much lower than this nominal value are not consistent with the observed variability of CO. Such models are also inconsistent with measurements of CO isotopic abundances, which imply the existence of plant sources.

Pinto, J. P.↗

NASA NTRS1982

Twenty three year cycle in surface temperatures during the Maunder minimum

Power spectra of Manley's record of central England temperatures for the Maunder minimum have been compared with later periods. It is found that the power in the approximately 23 year cycle is statistically significant in the Maunder minimum portion of this temperature time series. This gives indirect support to the recent suggestion that the solar cycle persisted in the Maunder minimum even though normal sunspot activity was not observed. The results also indicate that the approximately 23 year cycle was stronger during the Maunder minimum than later times in this record.

Hameed, S.↗

NASA NTRS1981

Implications of natural sources for the latitudinal gradients of NO/y/ in the unpolluted troposphere

The latitudinal distributions of tropospheric odd nitrogen (NO/y/) due to lightning discharges and stratospheric injection are studied by estimating latitude dependences of the sources and the rainout sink from data obtained in August-September, 1977, and May-June, 1978, during project GAMETAG. A one-dimensional (latitude dependent) model is developed for the annually, zonally, and vertically averaged concentration of trace species, NO(y) being treated as a single species, which decouples the NO(y) calculation from the rest of the model since NO(y) has no chemical sources or sinks in the troposphere. The equation governing the NO(y) distribution is solved using finite differences with 33 uniformly spaced grid points in the micron range of -1 to 1. The distribution due to the stratospheric source has a minimum in the tropics, and there are broad maxima centered in the 25-30 degree region in both hemispheres. The calculated NO(y) due to lightning has a maximum near 15 degrees S, and it decreases to nearly a fourth of the maximum value near the poles. The drop off from the maximum is sharper in the Southern Hemisphere in comparison with the Northern Hemisphere.

Hameed, S.↗

NASA NTRS1980

Response of the global climate to changes in atmospheric chemical composition due to fossil fuel burning

Recent modeling of atmospheric chemical processes (Logan et al, 1978; Hameed et al, 1979) suggests that tropospheric ozone and methane might significantly increase in the future as the result of increasing anthropogenic emissions of CO, NO(x), and CH4 due to fossil fuel burning. Since O3 and CH4 are both greenhouse gases, increases in their concentrations could augment global warming due to larger future amounts of atmospheric CO2. To test the possible climatic impact of changes in tropospheric chemical composition, a zonal energy-balance climate model has been combined with a vertically averaged tropospheric chemical model. The latter model includes all relevant chemical reactions which affect species derived from H2O, O2, CH4, and NO(x). The climate model correspondingly incorporates changes in the infrared heating of the surface-troposphere system resulting from chemically induced changes in tropospheric ozone and methane. This coupled climate-chemical model indicates that global climate is sensitive to changes in emissions of CO, NO(x) and CH4, and that future increases in these emissions could augment global warming due to increasing atmospheric CO2.

Hameed, S.↗

NASA NTRS1980

Impact of a global warming on biospheric sources of methane and its climatic consequences

Most of atmospheric methane originates by bacterial processes in anaerobic environments within the soil which are found to become more productive with increases in ambient temperature. A warming of climate, due to increasing levels of industrial gases resulting from fossil fuel burning, is thus likely to increase methane abundance within the atmosphere. This may lead to further heating of the atmosphere, since both methane and ozone (which is generated in the troposphere from reactions of methane) have greenhouse effects. This feedback mechanism has been explored with the use of a coupled climate-chemical model of the troposphere, by the calculation of the impact of the predicted global warming due to increased emissions of carbon dioxide and other industrial gases on the biospheric sources of methane.

Hameed, S.↗

NASA NTRS1980

Response of the global climate to changes in atmospheric chemical composition due to fossil fuel burning

Tropospheric ozone and methane might increase in the future as the result of increasing anthropogenic emissions of CO, NOx and CH4 due to fossil fuel burning. Since O3 and CH4 are both greenhouse gases, increases in their concentrations could augment global warming due to larger future amounts of atmospheric CO2. To test this possible climatic impact, a zonal energy-balance climate model has been combined with a vertically-averaged tropospheric chemical model. The latter model includes all relevant chemical reactions which affect species derived from H2O, O2, CH4 and NOx. The climate model correspondingly incorporates changes in the infrared heating of the surface-troposphere system resulting from chemically induced changes in tropospheric ozone and methane. This coupled climate-chemical model indicates that global climate is sensitive to changes in emissions of CO, NOx and CH4, and that future increases in these emissions could enhance global warming due to increasing atmospheric CO2.

Cess, R. D.↗

NASA NTRS1979

Latitudinal distribution of the sources of carbon monoxide in the troposphere

A vertically and zonally averaged model of the troposphere has been constructed which calculates photochemical interactions and diffusive North-South transport of trace species. The model can be used to calculate the latitudinal distribution of the source function of a species if its concentration distribution is known. This procedure has been applied to carbon monoxide and large sources have been found outside the industrialized belt in the Northern Hemisphere.

Hameed, S.↗

NASA NTRS1979

Sensitivity of the predicted CO-OH-CH4 perturbation to tropospheric NOx concentrations

Measurements indicate that ambient NOx(NO + NO2) concentrations vary over at least an order of magnitude in the troposphere. Thus it is of interest to study atmospheric chemistry with NOx concentrations covering this range. In this paper we present steady state calculations which show that as NOx concentrations are increased from very low values, the hydroxyl radical concentration increases at first and then decreases. This change of behavior occurs at a concentration of NO2 of about 0.23 ppb in the model. Also, the response of the atmosphere to increased CO fluxes undergoes a qualitative change as a function of the concentration of NOx. At low levels of NOx concentration, an increase in CO fluxes into the atmosphere depletes the OH concentration and increases the concentrations of CH4 and H2, as reported in the literature. However, at high values of NOx concentration, increased CO fluxes give rise to an increase in the OH concentration and, consequently, a decrease in the concentrations of CH4 and H2.

Hameed, S.↗

NASA NTRS1978

The natural and perturbed troposphere

A quantitative assessment of the chemical and climatic effects of industrial emissions into the atmosphere requires an understanding of the complex interactions of species within the atmosphere and of the atmosphere with other physical systems such as the oceans, lithosphere, and biosphere. The concentration of a particular species is determined by competition between various production and loss processes. The abundances of tropospheric gases are examined. The reactions of the members of the oxygen group are considered along with the models which have been developed to describe the involved relationships. Attention is also given to the natural carbon cycle, perturbations to the carbon cycle, the natural nitrogen cycle, perturbations to the nitrogen cycle, the hydrogen group, the sulfur group, and the halogen group.

Stewart, R. W.↗

NASA NTRS1978

Tropospheric ozone

Photochemical equilibrium models have been used to study the effect of recent revisions in important chemical reaction rates on the calculated tropospheric ozone concentration. Reasonable agreement with observed values is obtained if the NO(x) background is approximately 0.02 to 0.03 ppb, about an order of magnitude less than used in many previous model studies, but consistent with present nitrogen budget considerations and with observations of NO2. Chemical production and loss of ozone may dominate transport terms depending on values of key chemical rate constants and of the NO(x) background. This is consistent with the structure observed in the mean annual latitudinal distribution of ozone since ozone is its own chemical precursor and regions of enhanced stratosphere-troposphere exchange are also regions of enhanced photochemical activity.

Stewart, R. W.↗

NASA NTRS1977

Photochemistry of tropospheric ozone

A photochemical equilibrium model of minor constituent chemistry in the troposphere was constructed to investigate the photochemistry of tropospheric ozone. We find that photochemical production must be supplemented by additional sources to account for observed ozone levels in clean air, while photochemical loss is more important than surface destruction as an ozone loss mechanism. Photochemically produced ozone is sensitive to the NO(x) background in the model, exhibiting a maximum of about 0.5 ppb of NO(x).

Stewart, R. W.↗

NASA NTRS1976

Laws of effluent dispersion in the steady-state atmospheric surface layer in stable and unstable conditions

The two-dimensional diffusion equation has been solved by an integral method to obtain the distribution of ground-level concentration of an inert effluent emitted from a semi-infinite area source in a steady-state and horizontally homogeneous atmospheric surface layer. Mean wind velocity and eddy diffusivity profiles derived from empirically determined flux-profile relations of Businger et al. (1971) for stable and unstable surface layers were used. It is found that concentration as a function of downwind distance can be described by a simple formula over distances of practical interest in surface layer dispersion. Corresponding results for a cross-wind infinite line source are obtained by simple differentiation. The concentration distribution is completely determined by the friction velocity, the Monin-Obukhov length, the roughness length, and the effluent source strength. The generalization of the integral method needed to obtain accurate solutions of the diffusion equation with the given wind velocity and diffusivity profiles is discussed in an appendix.

Lebedeff, S. A.↗

NASA NTRS1976

A model study of the impact of emission control strategies on Los Angeles air quality

A generalized cell model is developed for the calculation of city-wide averages of photochemical smog components in Los Angeles. This model takes into account the effects of variations with time and within the city of the source strengths, the wind field, and the mixing depth. The effect of the influx of background pollution from outside the modeled volume is also included. Several control strategies for reducing automobile emissions are then introduced into the model, and their impact on predicted pollutant levels, particularly those of O3, are investigated.

Hameed, S.↗