Formation Of Sulfate Particles Research Articles

Simulation of formation and growth of atmospheric sulfate particles

This paper investigates the formation and growth of aerosol sulfate particles in the atmosphere. The evolution of the aerosol size distribution with time was modeled using the aerosol general dynamic equation. This equation was solved numerically using a discrete-nodal point method to describe the particle size distribution. For the initial size distribution we have used an average urban accumulation mode. The first step in our model considers the oxidation of SO 2 by OH radicals, producing H 2SO 4 (g). The next step considers the binary nucleation and condensation of the H 2SO 4H 2O system and its evolution due to coagulation and deposition mechanisms. A detailed description of the model is presented. The mass size distribution at different distances during the transport of the initial aerosol size distribution is also presented. The importance of different mechanisms on the evolution of the aerosol size distribution is discussed. Sensitivity analysis was performed for many model parameters where simulations were made at varying temperature, relative humidity and photo-oxidation rate conditions. Model calculations suggest that condensation growth is the dominant mechanism for the evolution of the size distribution of sulfate particles during moderate relative humidity conditions.

Observations of Near-Zero Ozone Concentrations Over the Convective Pacific: Effects on Air Chemistry

A series of measurements over the equatorial Pacific in March 1993 showed that the volume mixing ratios of ozone were frequently well below 10 nanomoles per mole both in the marine boundary layer (MBL) and between 10 kilometers and the tropopause. These latter unexpected results emphasize the enormous variability of tropical tropospheric ozone and hydroxyl concentrations, which determine the oxidizing efficiency of the troposphere. They also imply a convective short circuit of marine gaseous emissions, such as dimethyl sulfide, between the MBL and the uppermost troposphere, leading, for instance, to sulfate particle formation.

Enhanced formation and development of sulfate particles due to marine boundary layer circulation

Production and the subsequent development of sulfur‐derived particles in the marine boundary layer have been of great interest due to their potential role in modifying the radiative properties of marine stratiform clouds. In this work these phenomena were studied using a dynamic air parcel model, with the emphasis placed on examining how the boundary layer dynamics affects the system. Our simulations suggest that a homogeneous or steady boundary layer assumption may lead to a considerable underestimation of the number of nuclei formed. Further, we showed that if the observed particle size distributions and nonsea‐salt fraction of cloud condensation nuclei (CCN) production are to be explained by in situ particle production and growth, the sulfuric acid accommodation coefficient onto nuclei must be greater than 0.1 under conditions typical for clean marine areas. These high values require either a sulfuric acid vapor source in addition to SO2(g) oxidation or a H2SO4(g) accommodation coefficient onto more aged particles which is less than that onto nuclei. Both these options were tested and can be considered viable based on our present understanding of the marine environment. Finally, we showed that a nighttime interaction of the boundary layer air with clouds does not significantly affect nuclei formation or growth, but may lead to significant scavenging of fresh nuclei if their sulfuric acid accommodation coefficient is small. Cloud interactions during photochemically active periods may completely inhibit new particle production, and the growth of preexisting nuclei is likely to be significantly decelerated.

Temporal Variations of Particulate Air Pollution: A Marker for Free Radical Dosage and Adverse Health Effects?

AbstractStatistical associations have been observed between human mortality and fine and sulfate particles. However, significant gaps in our knowledge exist in explaining the observed health effects based on results from controlled exposure studies. It is possible that the causative agent is a species that is correlated with particulate matter, but not measured by routine sampling of atmospheric aerosols. Free radicals, such as hydroxyl radicals, are responsible for the formation of fine and sulfate particles. They are also known to be damaging to lung tissue, as well as playing a role in the pathogenesis of a wide variety of disease states, including inflammation and cancer. These observations suggest that radicals may be at least partly responsible for adverse health effects, and that fine particle mass could serve as a marker for free radical dosage. Applying receptor models to time-series aerosol data to determine the temporal variations of source contributions may provide additional insight regarding...

Aerosol nucleation in the winter Arctic and Antarctic stratospheres

We calculate the formation rate of sulfuric acid ‐ water aerosol particles as a function of altitude for the conditions of the winter Arctic and Antarctic stratospheres. The theoretical results indicate that sulfate particle formation can occur in the polar winter stratosphere. Conditions for new particle formation are increasingly favorable as the altitude increases between 20 and 30 km because of the decrease in surface area of pre‐existing particles and increasing sulfuric acid vapor supply. The theoretical predictions are consistent with observations of a high altitude CN layer over Antarctica in the spring. Available vapor pressure data indicate that ternary system particles composed of sulfuric acid, nitric acid and water are not thermodynamically stable under winter stratospheric conditions.

Backscatter laser depolarization studies of simulated stratospheric aerosols: crystallized sulfuric acid droplets

The optical depolarizing properties of simulated stratospheric aerosols were studied in laboratory laser (0.633 microm) backscattering experiments for application to polarization lidar observations. Clouds composed of sulfuric acid solution droplets, some treated with ammonia gas, were observed during evaporation. The results indicate that the formation of minute ammonium sulfate particles from the evaporation of acid droplets produces linear depolarization ratios of delta approximately 0.02, but delta approximately 0.10-0.15 are generated from acid droplet crystallization effects associated with recycled aerosols and the introduction of ammonia gas into the chamber. It is concluded that partially crystallized sulfuric acid droplets are a likely candidate for explaining the lidar delta approximately 0.10 values that have been observed in the lower stratosphere in the absence of the relatively strong backscattering from homogeneous sulfuric acid droplet (delta approximately 0) or ice crystal (delta approximately 0.5) clouds.

The Rate of SO2to Sulfate Particle Formation in an Air Parcel from an Oil Sands Extraction Plant Plume

A field program was conducted to determine the transformation of sulfur dioxide to particulate sulfate in the emissions from oil sands extraction plants near Fort McMurray, Alberta. Measurements were made under cold winter conditions during March and December 1983 and warm summer conditions during June 1984. The transformation rates of SO2 to SO4 were determined by tracking a single parcel of air emitted from the stack using an instrumented aircraft. Two methods were employed: the aerosol excess volume production and chemical analysis of particles collected on filters. The conversion rate varied from 0 to 2.81 percent per hour in the winter and 0 to 6.01 percent per hour in the summer. The significant oxidation of SO2 to SO4 observed during wintertime and early morning periods in the summer, and the considerable amounts of excess aerosol volume production of particles larger than 1.0 μm suggest that heterogeneous conversion may be appreciable close to the emission source, when the SO2 and aerosol concentr...

On the chemistry of stratospheric SO2 from volcanic eruptions

The April 4, 1982, eruption of El Chichón in southern Mexico introduced several megatons of gaseous sulfur into the stratosphere, mostly as SO2 or H2S. Available kinetic information indicates that H2S is converted to SO2 much faster than SO2 is oxidized to sulfate by homogeneous gas phase reactions. The process by which SO2 is chemically converted to sulfate is not precisely known, and various reaction mechanisms have been proposed. The rate‐limiting step of SO2 oxidation is believed to be reaction with the OH radical to form the HOSO2 radical. Depending on the fate of HOSO2, odd hydrogen may or may not be regenerated in the overall oxidation sequence. A decrease in OH due to volcanic SO2 should be observable through the gaseous species that depend on OH, and in particular SO2 itself. One‐ and two‐dimensional model results are presented that estimate the photochemical effects of the SO2 from the El Chichón volcano under various assumptions of HOSO2 to sulfate conversion. It is found that the chemical lifetime for the volcanic SO2 would be greater than 100 days for a large portion of the cloud if HOSO2 does not regenerate odd hydrogen during conversion to sulfate and if heterogeneous losses of SO2 are not competitive. However, observations of sulfate particle formation and SO2 imply a chemical lifetime of 30–40 days, which is consistent with HOSO2 conversion regenerating odd hydrogen. The implications of this finding for the problem of sulfate formation in the polluted troposphere is briefly reviewed.

Chemical Analysis of Size-Segregated Samples of Denver’s Ambient Particulate

Size-segregated impactor samples of Denver's wintertime airborne particulate were analyzed for the major chemical species. These species are responsible for most of the pollution-related visibility reduction in Denver. Samples were collected three times a day during a 40-day field program in November-December, 1978. Each of the measured chemical species (sulfate, nitrate, ammonium, bromide, organic and elemental carbon) had a log-normally distributed accumulation mode with a mass median aerodynamic diameter near 0.3 ..mu..m. For all species, particle size increased with increasing relative humidity. These results are supported by electrical aerosol analyzer (EAA) measurements. The impactor results for this time period are consistent with a photochemical mechanism for particulate nitrate formation and a heterogeneous mechanism for the formation of sulfate particles. 23 references, 5 figures, 5 tables.

On the sulfate, chloride and sodium concentration in maritime air around the Asian continent

On the basis of chemical analysis of aerosol samples collected over the seas around the Asian continent, the sulfate, chloride and sodium concentrations in maritime air are presented. By using the sodium content of the air and the average composition of the sea water, the magnitude of the chloride loss from sea-salt as well as the excess sulfate concentration are calculated. The results are discussed from the point of view of the HCl cycle and sulfate particle formation. DOI: 10.1111/j.2153-3490.1981.tb01760.x

Formation of Sulfate Particles in the Plume of the Four Corners Power Plant

Abstract On 6 June 1978, the Four Corners coal-fired power plant plume near Farmington, New Mexico, was sampled with an instrumented twin-engine Aero-commander 680E, up to 90 km downwind from the source. Measurements consisted of aerosol size distribution, condensation nuclei, various gases, individual particle chemistry using electron microscopy techniques and meteorological parameters. A substantial formation of condensation nuclei took place downwind of the plant at a rate of 1.3 × 1016 s−1 in the first 0.3 h, 3.3 × 1017 s−1 up to 2.5 h, and 8 × 1017 s−1 in the 2.5–12.5 h plume travel time. The corresponding conversion rates were 0.15, 0.5 and 0.3% h−1, respectively. The conversion rate due to oxidation of SO2 on surfaces of fly ash particles was negligible. Dry removal of particles was very high and reached an estimated maximum of 36% during the first 2.5 h probably due to partial impingements of the plume to the ground. Analysis of individual particles collected on nuclepore filters using a scanning ...

Sulfate particle formation by heteromolecular nucleation and condesation in cavities : By P. Hamill, Systems and Applied Sciences Corporation, NASA Langley Research Center, Hampton, VA 23665, U.S.A.

Sulfate particle formation by heteromolecular nucleation and condesation in cavities : By P. Hamill, Systems and Applied Sciences Corporation, NASA Langley Research Center, Hampton, VA 23665, U.S.A.

Sulfate particle formation by heteromolecular nucleation and condensation in cavities

The theory of heteromolecular nucleation of water—sulfuric acid solutions in cavities is developed. The time required to form sulfuric acid droplets by cavity nucleation followed by heteromolecular condensation is evaluated. Application to liquid phase SO 2 oxidation is discussed.

A chemical model for urban plumes: Test for ozone and particulate sulfur formation in St. Louis urban plume

A chemical model with anthropogenic sources of nitrogen oxides and hydrocarbons is applied to simulate the chemical behaviour of pollutants in the St. Louis urban plume. It is suggested that a substantial increase in peroxy radical concentrations (HO 2,RO 2) in the polluted air mass outside its source region leads to an effective formation of secondary pollutants like ozone and sulfate particles. The model indicates characteristic time for ozone generation in the plume of a few hours. Maximum ozone mixing ratio of 115 ppb is predicted after 4 h transport time outside the source region. Conversion rates of SO 2 to H 2SO 4 through gas phase reactions with hydroxyl and peroxy radicals are estimated to be 1–5%h −1. This leads to an approx 25% conversion of SO 2 to paniculate sulfur in the plume during the day. Agreement with measured ozone concentrations and flow rates of ozone and participate sulfur in the St. Louis plume on 18 July 1975 can be taken as strong indications that ozone and sulfate particle formation in the plume proceeds through the suggested mechanisms.

Seasonal and diurnal variations of the size distribution of atmospheric sulfate particles

Measurements were carried out to determine the seasonal and diurnal variations of the size distribution of sulfate particles. The results of these measurements show that there is an unambiguous seasonal variation which is caused by the changes of the relative humidity of the air. On the other hand no diurnal variation was found because during the sampling time the relative humidity was smaller than the value necessary for the phase transition of the particles. The measured growth with increasing relative humidity of the mass median radius of sulfate particles is practically comparable with the theoretical growth of a pure ammonium sulfate particle having a 0.14 ? dry radius. On the basis of these findings the mechanism of the sulfate particle formation is briefly discussed. DOI: 10.1111/j.2153-3490.1970.tb01525.x