Particulate Sulfate Concentrations Research Articles

Short-Term Variations in Aerosol Components during the Same Asian Dust (Kosa) Event Observed in Nagasaki, Japan and Beijing, China

We carried out short-term continuous monitoring of Asian dust every 2 hours in Beijing, China and Nagasaki, Japan and performed chemical analyses during 2 events where there were large differences in the characteristics of the Asian dust blowing into Nagasaki. The first involved typical Asian dust that originated in the Mongolian Gobi Desert on March 30, 2007 (abbreviated to TAD 2007). The second involved a polluted air parcel that arrived in Japan along with Asian dust on May 8, 2007. By comparing temporal changes in PM10 and particulate sulfur (sulfate ions) concentrations with the timing of the Asian dust arrival, we found in the April event (TAD 2007) that the polluted air parcel covering Beijing did not mix with an air parcel containing TAD 2007 coming from the north. In the May event, we inferred that mixing of the polluted air parcel and an air parcel containing Asian dust had occurred. The composition of aerosol particles in the air parcel reaching Nagasaki in the April event reflected the chemical composition of TAD 2007 itself, whereas that of the May event had high concentrations of chemical components originating in anthropogenic pollution, such as sulfate ions, zinc, lead and other heavy metals.

Aerosol layers from the 2008 eruptions of Mount Okmok and Mount Kasatochi: In situ upper troposphere and lower stratosphere measurements of sulfate and organics over Europe

In 2008 Mount Okmok and Mount Kasatochi started erupting on 12 July and 7 August, respectively, in the Aleutians, depositing emissions of trace gases and aerosols as high as 15.2 km into the atmosphere. During an aircraft campaign, conducted over Europe in between 27 October and 2 November 2008, the volcanic aerosol was measured by an Aerodyne aerosol mass spectrometer, capable of particle chemical composition measurements covering a size diameter range between 40 nm and 1 μm. In the volcanic aerosol layer enhanced submicron particulate sulfate concentrations of up to 2.0 μg m−3 standard temperature and pressure (STP) were observed between 8 and 12 km altitude, while background values did not exceed 0.5 μg m−3 (STP). Twenty‐one percent of the volcanic aerosol consisted of carbonaceous material that increased by a factor of 1.9 in mass compared to the free troposphere. Enhanced gaseous sulfur dioxide concentrations measured by an ion trap chemical ionization mass spectrometer of up to 1.3 μg m−3 were encountered. An onboard radiation measurement system simultaneously detected an enhanced aerosol signal. Furthermore, two German lidar stations identified an aerosol layer before and after the campaign. Data analysis shows that the aerosol layer was observed mainly in the lowermost stratosphere. Correlation of particulate sulfate concentration and sulfur dioxide mixing ratios indicates that after a 3 month residence time in the stratosphere, not all sulfur dioxide has been converted into sulfate aerosol. The significant fraction of organic material might have implications on heterogeneous chemistry in the stratosphere, which need to be explored more thoroughly.

Influence of the 2008 Kasatochi volcanic eruption on sulfurous and carbonaceous aerosol constituents in the lower stratosphere

Influences on stratospheric aerosol during the first four months following the eruption of Kasatochi volcano (Alaska) were studied using observations at 10700 ± 600 m altitude from the CARIBIC platform. Collected aerosol samples were analyzed for elemental constituents. Particle number concentrations were recorded in three size intervals together with ozone mixing ratios and slant column densities of SO2. The eruption increased particulate sulfur concentrations by a factor of up to 10 compared to periods before the eruption (1999–2002 and 2005–August 2008). Three to four months later, the concentration was still elevated by a factor of 3 in the lowermost stratosphere at northern midlatitudes. Besides sulfur, the Kasatochi aerosol contained a significant carbonaceous component and ash that declined in time after the eruption. The carbon‐to‐sulfur mass concentration ratio of the volcanic aerosol was 2.6 seven days after the eruption and reached 1.2 after 3–4 months.

Development and application of a computationally efficient particulate matter apportionment algorithm in a three-dimensional chemical transport model

An on-line and an off-line version of a computationally efficient particulate matter source apportionment algorithm have been developed and compared using the three-dimensional chemical transport model PMCAMx. Both versions of the algorithm use source specific-species that track the contributions of source locations or source classes. The two versions showed a good agreement with each other and with more accurate, computationally demanding methods. The off-line algorithm (Particulate Source Apportionment Technology, PSAT) is simpler to implement, has a lower computational cost and is suitable for a range of source apportionment studies. As a first application, PSAT was used to investigate the contribution of power plant SO 2 emissions to particulate sulfate concentrations in the Eastern United States. The impact of the transport of SO 2 emissions from the Chicago, IL area and the impact of these emissions on particulate sulfate concentration in surrounding areas were also studied as a second application. The implementation of PSAT for the SO 2/particulate sulfate system only resulted in a 1% increase in computation time over the base simulation. The algorithm provides a computationally efficient platform for the study of pollutant transport and source contributions on regional scales.

Atmospheric concentrations of nitric acid, sulfur dioxide, particulate nitrate and particulate sulfate, and estimation of their dry deposition on the urban- and mountain-facing sides of Mt. Gokurakuji, Western Japan

Atmospheric concentrations of nitric acid (HNO3), sulfur dioxide (SO2), particulate nitrate (NO3-) and particulate sulfate (SO4(2-)) on the urban- and mountain-facing sides of Mt. Gokurakuji were measured from November 2002 to October 2003, in order to evaluate the effects of anthropogenic activity on air quality and dry deposited nitrate and sulfate on the surfaces of pine foliage. The results showed that HNO3, SO2 and NO3(-) concentrations were significantly higher (P < 0.05) on the urban-facing side (1.54, 2.48 and 0.65 microg m(-3), respectively) than the mountain-facing side (0.67, 1.19 and 0.37 microg m(-3), respectively), while SO4(2-) concentrations did not differ significantly between the two sides (urban-facing: 2.80 microg m(-3); mountain-facing: 2.05 microg m(-3)). Indirect estimates of dry deposition rates of nitrate and sulfate to the surfaces of pine foliage based on the measured concentrations approximately agreed with the measured values determined by the foliar rinsing technique in a previous study. It was found that HNO3 was the major source (approximately 80%) of dry deposited nitrate on pine foliage, while the contribution from SO4(2-) was about equal to that from SO2. In conclusion, HNO3 and SO2 appear to be dominant species reflecting higher dry deposition rates of nitrate and sulfate on the urban-facing side compared to the mountain-facing side of Mt. Gokurakuji.

Calibration techniques and sampling resolution requirements for groundtruthing multibeam acoustic backscatter (EM3000) and QTC VIEW™ classification technology

Both acoustic and sediment surveys were carried out in the Broughton Archipelago, British Columbia, in order to map a former aquaculture site and calibrate acoustic surveys with georeferenced sediment properties. The acoustic surveys included EM3000 Multibeam (including backscatter) and QTC VIEW™ (Series IV) technologies, while the geotechnical survey entailed Van Veen grab sampling of surface sediments and associated analyses. The two acoustic technologies were consistent in their ability to identify distinct regions of seafloor characterized by rock outcrops, consolidated substrates, or gel-mud depositional fields. Both multibeam backscatter data and QTC VIEW™ number-coded classifications were extracted across a range of circular areas located at each georeferenced sampling station (radii: 2, 3, 4, 5, 8, 12, 16, 20 m). Statistical correlations were observed between backscatter and certain geotechnical properties, such as sediment porosity, sediment grain size fractions (<2 μm, silt content), and particulate sulfur concentration. The areal resolution of backscatter extraction was explored in terms of determining a sensitive calibration technique between backscatter and sediment properties. In general the highest r 2 values between backscatter and sediment variables were observed across extraction radii between 8 and 20 m. Such groundtruthing techniques could be used to interpolate seafloor characteristics between sampling stations and provide a steering tool for sampling designs associated with benthic monitoring programs.

Association of airmass transport patterns and particulate sulfur concentrations at Big Bend National Park, Texas

The Big Bend Regional Aerosol and Visibility Observational (BRAVO) study was initiated to understand the causes of haze at Big Bend National Park. BRAVO included the measurement of aerosols throughout Texas from July to October 1999 and extensive modeling of these aerosols. In support of BRAVO, the potential contributions from source regions to particulate sulfur at Big Bend during the BRAVO period were examined via an airmass history analysis. This was done using residence time analysis and a new technique of decomposing the residence time probability density function into its basic components, an airmass transport directional frequency and inverse characteristic transport speed. Trajectory heights over potential source regions were also examined. The system was validated using inert perfluorocarbon tracers that were released from four Texas sites. Airmass transport to Big Bend was examined on days with high (>80th percentile), and days with low (<20th percentile), particulate sulfur. High particulate sulfur concentrations were associated with low-level and low-speed airmass transport from the eastern United States, eastern Texas, and northeastern Mexico. All three of these regions have high SO 2 emissions that could contribute to Big Bend's haze. Examination of individual trajectories showed that the highest particulate sulfur concentrations occurred when transport over several of these regions coincided. Low particulate sulfur concentrations coincided with low-level but high-speed airmass transport from the Gulf of Mexico and along the Mexico–Texas border. Precipitation often occurred along these trajectories. Low sulfur was also associated with transport from low SO 2 emission regions north and west of Big Bend. Days with high SO 2 or selenium concentrations were also examined. High SO 2 concentrations were associated with prior transport from nearby sources, particularly the Carbón power plants located in Mexico ∼230 km southeast of Big Bend. High selenium concentrations were associated with prior transport over Carbón and eastern Texas.

The regional influence of volcanic emissions from Popocatéptl, Mexico: Discussion of “Measurement of aerosol particles, gases and flux radiation in the Pico de Orizaba Nacional Park, and its relationship to air pollution transport”, Márquez et al., 2005, Atmospheric Environment, 39, 3877–3890

An understanding of the influence of anthropogenic and natural point sources of pollution on the compositions of distant airmasses requires the careful collection of atmospheric composition data over extended periods of time. Equally, a proper understanding of the influence of megacities, biomass burning plumes and persistent volcanic emissions on the oxidising capacity of the atmosphere requires analysis of the downstream fate of their associated gas and aerosol plumes. Marquez et al. (2005) recently presented some interesting data on the compositions of ambient atmospheric gases and particles at a sampling site in Mexico (Pico de Orizaba National Park, elevation 3300 m; Fig. 1) in late February and early March 2001. Two notable features of their data were the high concentrations of SO2 (mean value 14 ppb) and particulate sulphate (mean 5 μg m−3). The authors ascribed these features to the arrival of air from urban sources nearby, either Mexico City (200 km to the west, elevation 2240 m) or Puebla City (70 km to the west, elevation 2160 m). However, airmass parcels which arrive at the sampling location from either Mexico City, or Puebla, are likely to have passed close to the active volcano of Popocatepetl, 160 km from the sampling endpoint (Fig. 1). In their original paper, Marquez et al. (2005) dismissed any possible volcanic influence on their sampling on the basis of the absence of any volcanic (ash) plume visible in AVHRR weather satellite data. However, Popocatepetl, like many volcanoes, is a prodigious source of reactive gas and aerosol even in the absence of any visible ash plumes. ‘Passively’ degassing volcanoes are becoming increasingly well known as major contributors to the tropospheric gas and aerosol burden, and in particular that of SO2, sulphate and other particles

Characteristics and origin of lowermost stratospheric aerosol at northern midlatitudes under volcanically quiescent conditions based on CARIBIC observations

Characteristics and origin of the aerosol in the lowermost stratosphere at northern midlatitudes were studied using measurements from a passenger aircraft (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, or CARIBIC). Aerosol samples were collected during 60 intercontinental flights during 1999–2002 and analyzed for elemental composition with particle‐induced X‐ray emission (PIXE). Concurrent measurements of trace gases were used to interpret the aerosol measurements. It was found that particulate sulfur concentration increased steadily in the potential vorticity (PV) region of 2–7 PVU, whereas particulate potassium and iron showed no such dependence. The variability in concentration of the latter two elements was mainly connected with season, similar to their variation in the upper troposphere, whereas PV dominated the particulate sulfur variability. An ozone‐based model was developed to quantitatively determine the mixing of stratospheric and tropospheric air masses. A significant dependence on PV was found, and the stratospheric fraction of the air peaked during spring. It was found that the particulate sulfur concentration was strongly dependent on the origin of the air masses. The concentration increased by a factor of 3 over the lowermost stratosphere. A discontinuity in the concentration over the tropopause indicated particle formation from sulfur dioxide transported across the tropopause. The concentration at the top of the lowermost stratosphere was used to estimate that the particulate sulfur production in the stratosphere is 0.066 Tg S/yr with approximately half of the amount transported across the top of the lowermost stratosphere originating in carbonyl sulfide.

Characteristics in Concentration of Chemical Species in Ambient Air Based on Three-Year Monitoring by Filter Pack Method

Continuous monitoring of concentrations of particulate matter and gaseous compounds for three years by a four-stage filter-pack method clarified the characteristics in the concentrations of chemical species in particulate matter and gaseous compounds in ambient air in Kobe, Japan. The amount of materials in blank filters was low enough for this method to be used for the monitoring of ambient air. Little or none of the hydrogen chloride was derived anthropogenically. The concentrations of both particulate sulfate and sulfur dioxide in spring and summer were significantly higher than those in autumn and winter. The concentration of gaseous nitric acid was high in summer, which suggests that active photochemical reactions in the atmosphere provided more nitrogen species in summer. The measured concentration products [HNO3][NH3] showed good agreement with the theoretical predictions with some exceptions. The total concentration of ammonium species showed no significant seasonal variation except that the concentration in winter was low. The concentration of nss-Ca2+ in spring was significantly higher than that in the other seasons, which is most likely associated with the so-called yellow-sand events. The concentrations of nss-K+ and nss-Ca2+ accounted for most of K+ and Ca2+, respectively, whereas that of nss-Mg2+ accounted for only 5% of Mg2+

An evaluation of TRACE‐P emission inventories from China using a regional model and chemical measurements

We evaluate the TRACE‐P emission inventories for gaseous and particulate pollutants from East Asia using chemical measurements made at a rural site in China during the China‐MAP Field Intensive in conjunction with a coupled regional climate/chemical transport modeling system. Time‐dependent, three‐dimensional fields for trace gas and particulate matter concentrations over East Asia are simulated by an updated version of the Regional Acid Deposition Model (RADM) driven by the TRACE‐P emission inventories along with meteorology fields calculated by the NCAR Regional Climate Model (RegCM) for the month of November 1999. Model‐calculated SO2 is in good agreement with measurements, while CO and particulate carbon (PC) are significantly smaller, and particulate sulfate (SO42−) is somewhat smaller. Our calculations suggest that increases in the TRACE‐P emission inventory of CO by ∼50% and PC by 60–90% would bring the model‐calculated CO, PC, and particulate sulfate concentration into agreement with the China‐MAP observations. If these increases were spread uniformly throughout China and the year, it would require that there be additional emissions in China of CO and PC of 60 Tg yr−1 and 2.5–4 Tg yr−1, respectively. Further analysis of high resolution gas species measurements suggests that the missing CO emissions are likely to be associated with SO2 emissions from coal burning. This in turn suggests that coal‐burning facilities in China are operating at significantly lower efficiencies than currently assumed.

Regional trends in rural sulfur concentrations

This paper presents an analysis of trends in atmospheric concentrations of sulfur dioxide (SO 2 ) and particulate sulfate (SO 4 2− ) at rural monitoring sites in the Clean Air Act Status and Trends Monitoring Network (CASTNet) from 1990 to 1999. A two-stage approach is used to estimate regional trends and standard errors in the Midwest and Mid-Atlantic regions of the US. In the first stage, a linear regression model is used to estimate site-specific trends in data adjusted for the effects of season and meteorology. In the second stage, kriging methodology based on maximum likelihood estimation is used to estimate regional trends and standard errors. The method is extended to include a Bayesian analysis to account for the uncertainty in estimating the spatial covariance parameters. For both pollutants, significant improvement in air quality was detected that appears similar to the large drop in SO 2 power plant emissions. Spatial patterns of trends in SO 2 and SO 4 2− concentrations vary by location over the eastern US. For SO 2 , trends at monitoring sites in the Midwest and Mid-Atlantic were in the −30% to −42% range with smaller changes in the South. Across most of the US, trends in SO 4 2− were smaller than for SO 2 . Both spatial prediction techniques produced similar results in terms of regional trends and standard errors.

New particle formation in anthropogenic plumes advecting from Asia observed during TRACE‐P

The characteristics and sources of what are believed to be newly formed 3 to 4 nm particles in anthropogenic plumes advecting from Asian are reported. Airborne measurements were made from March to April 2001 as part of the NASA TRACE‐P experiment at latitudes ranging from North of the Philippines to Northern Japan (20 to 45°N). In the more polluted plumes, high concentrations of 3 to 4 nm diameter particles (&gt;100cm−3) were observed both within and along the upper outer edges of plumes that were identified by enhanced carbon monoxide and fine particulate sulfate concentrations. The results from two research flights are investigated in detail. Three to four‐nm particle concentrations are generally correlated with gas phase sulfuric acid and found in regions of low surface areas relative to the immediate surroundings or where there are steep transitions to lower surface areas. Sulfuric acid and surface area concentrations in the most polluted plume reached 6 × 107 cm−3 and 750 μm2 cm−3, respectively, in regions of particle formation. In contrast to these anthropogenic plumes, few 3 to 4 nm particles were observed in the clean background and few were detected within a volcanic plume where the studies highest H2SO4 concentrations (&gt;108 cm−3) were recorded. Enhanced SO2 concentrations in the range of approximately 2 to 7 ppb, in conjunction with other unidentified, possibly coemitted species, appear to be the driving factor for nucleation.

Differences between corrosion products formed on copper exposed in Tokyo in summer and winter

We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu 2O and posnjakite Cu 4SO 4(OH) 6 · H 2O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate.

Trends in sulphate and nitrate wet deposition over the United Kingdom: 1986–1999

Since 1986 annual wet deposition of non-sea-salt sulphur has decreased over all regions of the United Kingdom, with the largest decrease in eastern areas. Nationally wet deposited sulphur has decreased by about one-third compared with an approximately two-thirds decrease in sulphur dioxide emissions. Over the same period daily measurements of sulphur dioxide and particulate sulphate concentrations at a small number of sites showed a statistically significant decrease at all but the most remote locations. The comparative magnitude of the changes in UK emissions and wet deposition suggests some change in the partitioning between wet and dry sulphur deposition. Trajectory analyses of precipitation events show that background sulphate deposition has not changed significantly in northwestern coastal regions, where it accounts for approximately half of the total. Wet nitrate deposition has decreased at a slower rate and increased slightly in some remote western areas. Sector analyses suggest that this increase is linked with increased deposition during easterly airflow while particulate sulphate concentrations in these airmasses have decreased. Nitrate now accounts for at least one-third of the acidifying effect of the combined wet deposition of non-sea-salt sulphate and nitrate over all parts of the United Kingdom.

Back-trajectory analyses of fine particulate matter measured at Big Bend National Park in the historical database and the 1996 scoping study

Analyses of the sources of fine particles associated with visibility reduction at Big Bend National Park during a 10-year period from 1989–1998 and from a regional visibility scoping study conducted during September and October 1996 at 19 sites in Texas and Mexico are summarized and compared. Fine sulfate particles are the largest fraction of the fine mass, and scattering by sulfates is estimated to be nearly half of the non-Rayleigh light extinction at Big Bend. Fine particulate sulfur concentrations are seasonal, with the highest values occurring during the summer and fall when back trajectory analyses show that air masses are most likely to arrive at Big Bend from the southeast after passing over Mexico or from areas to the northeast including east Texas. Episodically, high concentrations of fine mass and high light extinction values can be due to other species such as fine organic carbon or blowing soil dust. Organic carbon concentrations are often extremely high during the spring, especially during May. A combination of back trajectory analyses and the coincidence of high organic carbon and high non-soil potassium concentrations leads to the hypothesis that these concentrations are due to fires, primarily seasonal agricultural burning in Mexico and Central America. Fine soil concentrations often reach values that are twice the annual mean during July. These concentrations also frequently have high Al/Ca ratios, indicative of Saharan dust. Back trajectories associated with these events show air masses arriving from the southeast and are consistent with the hypothesis of transport of air masses from Africa during July. There is a high frequency of transport of air masses from Mexico to Big Bend, especially during the summer when fine mass concentrations and light extinction are highest. Therefore, sources and potential sources of sulfates and other fine particles in Mexico, particularly in areas southeast of the park have a high likelihood of contributing to visibility degradation at the park. Source areas to the northeast of the park, in east Texas and farther upwind also contribute to high fine sulfate concentrations.

Receptor modelling of PM 10 concentrations at a United Kingdom national network monitoring site in central London

A receptor model for predicting future PM 10 concentrations has been developed within the framework of the UK Airborne Particles Expert Group and applied during the recently completed review of the UK National Air Quality Strategy. The model uses a combination of measured PM 10, oxides of nitrogen and particulate sulphate concentrations to provide daily estimates of the contributions to total particle concentrations from primary combustion, secondary and other (generally coarse) particle sources. Projections of past and future concentrations of PM 10 are estimated by applying appropriate reductions to the current concentrations of the three components based on an understanding of the likely impact of current policies on future levels. Projections have been derived from 1996, 1997 and 1998 monitoring data and compared with UK national air quality objectives and European Union limit values. One of the key uncertainties within the receptor modelling method is the assignment of the residual PM 10, remaining after the assignment of primary combustion and secondary particle contributions, to the ‘other’ particle fraction. An examination of the difference between measured PM 10 and PM 2.5 concentrations confirms our assignment of the bulk of this residual to coarse particles. Projections based on 1996 monitoring data are the highest and those based on 1998 monitoring data are the lowest. Whilst there is considerable difference between these projections they are consistent with measured concentrations for previous years. All three projections suggest that with current agreed policies the EU annual mean limit value will be achieved. The 24-h mean limit value is projected to be achievable when projections are derived from 1997 and 1998 data, but not from 1996 data. All three projections suggest that with current agreed policies the central London site will not achieve the provisional 1997 UK National Air Quality Strategy objective.

Attribution of Particulate Sulfur in the Grand Canyon to Specific Point Sources Using Tracer-Aerosol Gradient Interpretive Technique (TAGIT)

ABSTRACT Since aerosol particulate sulfur is generally a secondary airborne pollutant, most source attribution techniques require many assumptions about the transport and chemistry of sulfur dioxide (SO2) emissions. Uncertainties in our understanding of these processes impair our ability to generate reliable attribution information that is necessary for designing cost-effective pollution control policies. A new attribution technique using artificial tracer is presented in hopes of reducing the uncertainty of secondary aerosol source attribution. The Tracer-Aerosol Gradient Interpretive Technique (TAGIT) uses tracer data from a monitoring network to distinguish sites impacted by a source tagged with tracer from nonimpacted sites. Sites determined not to be influenced by the plume are considered to represent background particulate sulfur concentrations. The particulate sulfur attributable to the source at sites within the plume is calculated as the difference between observed and background particulate sulfur. TAGIT is applied to measurements made in the vicinity of the east and west ends of the Grand Canyon in order to attribute particulate sulfur to the sources within the Eastern Colorado River Valley (ECRV) and the Mohave Power Project (MPP), respectively. TAGIT results indicate that during the winter intensive field sampling experiment (January 15–February 13, 1992), an average of 59 + 12% of the particulate sulfur at Marble Canyon, AZ, was attributable to ECRV sources. Similarly, during the summer field sampling experiment (July 13–August 30, 1992), MPP is estimated to have contributed an average of 7 + 3% of the particulate sulfur at Meadview, AZ. Uncertainties associated with the assumptions of TAGIT are discussed and quantified. The attribution results suggest that SO2-to-sulfate conversion rates are highly variable from day to day in this region.

Chemical characteristics of free tropospheric aerosols over the Japan Sea coast: aircraft-borne measurements

Atmospheric aerosol particulate matter was directly collected in the free troposphere over the Japan Sea coast between 1992 and 1994 using an aircraft-borne nine-stage cascade impactor (particle size range: 0.1–8 μm). The water-soluble components in the aerosol particulate matter were analyzed by ion chromatography. Particulate sulfate and ammonium were detected in most of the samples and their size distributions showed noticeable peaks below the 1 μm particle size range. Water-soluble calcium (Ca 2+) was detected in half of the samples; the size distribution showed that the maximum particle size was larger than 1 μm. Highly concentrated Ca 2+ in larger particles was possibly due to transport of Kosa aerosols from the Asian continent in the free troposphere. The concentration of fine particulate sulfate and ammonium tended to increase whenever Ca 2+ was detected, which suggests possible mixing of Kosa aerosols and non-Kosa aerosols during long-range transport of air masses containing Kosa particles.

Precision and Accuracy in the Determination of Sulfur Oxides, Fluoride, and Spherical Aluminosilicate Fly Ash Particles in Project MOHAVE

The precision and accuracy of the determination of particulate sulfate and fluoride, and gas phase S02 and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for highland low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m3 and ±2.5 nmol/m3 for the determination of S02 and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m3 and ±2.0 nmol/m3 for the determination of the same species with a high-volume or low-volume filter pack. The precision for the determination of the sum of HF(g) and fine particulate fluoride is +0.3 nmol/m3. The precision for the determination of aluminosilicate fly ash particles is ±100 particles/m3. At high concentrations of the various species, reproducibility of the various measurements is ±10% to ±14% of the measured concentration. The concentrations of sulfate determined using filter pack samplers are frequently higher than those determined using diffusion denuder sampling systems. The magnitude of the difference (e.g., 2-10 nmol sulfate/m3) is small, but important relative to the precision of the data and the concentrations of particulate sulfate present (typically 5-20 nmol sulfate/m3). The concentrations of S02(g) determined using a high-volume cascade impactor filter pack sampler are correspondingly lower than those obtained with diffusion denuder samplers. The concentrations of SOx (SOz(g) plus particulate sulfate) determined using the two samplers during Project MOHAVE at the Spirit Mountain, NV, and Hopi Point, AZ, sampling sites were in agreement. However, for samples collected at Painted Desert, AZ, and Meadview, AZ, the concentrations of SOx and S02(g) determined with a high-volume cascade impactor filter pack sampler were frequently lower than those determined using a diffusion denuder sampling system. These two sites had very low ambient relative humidity, an average of 25%. Possible causes of observed differences in the S02(g) and sulfate results obtained from different types of samplers are given.