Atmospheric Environment (v.37, #9-10)
Editorial board (i).
List for forthcoming papers (I-II).
James P. Lodge Jr. (February 4, 1926–December 14, 2001) by Purnendu K. Dasgupta (1155-1159).
James P. Lodge, Jr.: a tribute to a friend by Richard J Thompson (1160-1161).
James P. Lodge, Jr.: a tribute to an editor by Stephen E Schwart (1160).
Soil sample collection and analysis for the Fugitive Dust Characterization Study by Lowell L Ashbaugh; Omar F Carvacho; Michael S Brown; Judith C Chow; John G Watson; Karen C Magliano (1163-1173).
A unique set of soil samples was collected as part of the Fugitive Dust Characterization Study. The study was carried out to establish whether or not source profiles could be constructed using novel analytical methods that could distinguish soil dust sources from each other. The soil sources sampled included fields planted in cotton, almond, tomato, grape, and safflower, dairy and feedlot facilities, paved and unpaved roads (both urban and rural), an agricultural staging area, disturbed land with salt buildup, and construction areas where the topsoil had been removed. The samples were collected using a systematic procedure designed to reduce sampling bias, and were stored frozen to preserve possible organic signatures. For this paper the samples were characterized by particle size (percent sand, silt, and clay), dry silt content (used in EPA-recommended fugitive dust emission factors), carbon and nitrogen content, and potential to emit both PM10 and PM2.5. These are not the “novel analytical methods” referred to above; rather, it was the basic characterization of the samples to use in comparing analytical methods by other scientists contracted to the California Air Resources Board. The purpose of this paper is to document the methods used to collect the samples, the collection locations, the analysis of soil type and potential to emit PM10, and the sample variability, both within field and between fields of the same crop type.
Keywords: PM10; PM2.5; Source profiles; Soil dust; Dust emission;
Hourly concentrations and light scattering cross sections for fine particle sulfate at Big Bend National Park by Susanne V Hering; Mark R Stolzenburg; Jenny L Hand; Sonia M Kreidenweis; Taehyoung Lee; Jeffrey L Collett; David Dietrich; Mark Tigges (1175-1183).
Fine particle sulfate was measured continuously for 90 consecutive days, from August through October 1999, at Big Bend National Park. Measurements were made with a prototype integrated collection and vaporization cell, whereby particles are humidified and collected by impaction onto a metal strip and analyzed in place by flash-vaporization and pulsed fluorescence detection of the evolved sulfur dioxide. The time resolution was 12 min. Sulfate values are compared to 24-h integrated filter measurements. Time variation in observed concentrations are compared to hourly measurements of dry particle size distributions and to nephelometry at ambient humidity. For most of the study period the sulfate was the major constituent of the accumulation mode aerosol. The sulfate scattering cross section as a function of relative humidity is inferred by comparisons among these measurements using a two-component fine particle model wherein the nonsulfate accumulation mode volume is attributed to nonhygroscopic components.
Diagnostic evaluation of numerical air quality models with specialized ambient observations: testing the Community Multiscale Air Quality modeling system (CMAQ) at selected SOS 95 ground sites by J.R. Arnold; R.L. Dennis; G.S. Tonnesen (1185-1198).
Three probes for diagnosing photochemical dynamics are presented and applied to specialized ambient surface-level observations and to a numerical photochemical model to better understand rates of production and other process information in the atmosphere and in the model. However, care must be taken to ensure that rate and process information is not confounded by inappropriate averaging over these diurnally changing photochemical dynamics. One probe, the [O3] response surface probe [O3]/[NO X ], is used here as a chemical filter to select NO X -limited hours in the observations and the simulations. Other probes used here are the fraction NO Z /NO Y , a measure of chemical aging, and a measure of the production efficiency of O3 per NO X converted, [O3] to [NO Z ]. The key ambient measurements for all three probes are accurate [NO2] and a reliable estimate of total NO Y . Good agreement is shown between models and observations in cases where local photochemical production dominates and where model emissions inputs are thought to be mostly complete. We interpret this agreement to mean that the photochemical processing in CMAQ is substantially similar to that in the atmosphere. More importantly, we see that the three probes provide consistent information about photochemical processing, especially when used together.
Keywords: Photochemical modeling; Model evaluation; Ozone sensitivity indicators; Carbon Bond IV; Southern Oxidants Study;
On-line measurements of diesel nanoparticle composition and volatility by Hiromu Sakurai; Herbert J. Tobias; Kihong Park; Darrick Zarling; Kenneth S. Docherty; David B. Kittelson; Peter H. McMurry; Paul J. Ziemann (1199-1210).
A thermal desorption particle beam mass spectrometer (TDPBMS) and tandem differential mobility analyzers (TDMA) were used for on-line measurements of the chemical composition and volatility of nanoparticles and larger particles emitted from a modern, heavy-duty diesel engine operated at light and medium loads under laboratory conditions. Temperature-dependent TDPBMS mass spectra and mass spectra obtained using spectrally distinctive oil and synthetic Fischer–Tropsch fuel were analyzed using mass spectral matching methods to obtain quantitative information on the contributions of fuel, oil, oxidation products, and sulfuric acid to particle composition. TDMA measurements of volatility yielded information on nanoparticle vapor pressures and therefore on the composition of organic components. The results indicate that, for these operating conditions, the volatile component of both diesel nanoparticles and larger particles is comprised of at least 95% unburned lubricating oil. TDMA volatility measurements also detected residual species a few nanometers in diameter, which may be non-volatile cores (soot, metal oxide) or low-volatility organic compounds. These on-line analyses provide new insights into the mechanisms of diesel nanoparticle formation.
Keywords: Aerosol; Nucleation; Soot; Tandem differential mobility analyzer; Particle mass spectrometry;
Tracers of wood smoke by M.A.K Khalil; R.A Rasmussen (1211-1222).
Smoke from wood burning is a significant source of air pollution in many parts of the world. When several sources simultaneously cause air pollution, it is often difficult to determine how much comes from wood burning. Wood smoke has unique chemical characteristics that can be used as indicators, including elemental composition, particularly potassium and chlorine, the ratios of organic and elemental carbon, and gases such as methyl chloride. This paper deals with formulating and applying the chemical mass balance approach incorporating both gas- and aerosol-phase tracers to a study carried out at Olympia-Lacey in Washington. In this study, three types of tracers were measured simultaneously and used to estimate wood smoke pollution during Winter, namely elemental composition and organic carbon in the particle phase and methyl chloride in the gas phase. The results from the different tracers are found to be in agreement. The air pollution at the study site was dominated by wood smoke mostly from low-temperature combustion (about 80%), with additional but smaller contributions from oil furnaces (15%), automobiles (4%) and occasionally from other nearby sources.
Keywords: Methyl chloride; CH3Cl; Receptor model; CMB; Regional air pollution;
A closure study of aerosol mass concentration measurements: comparison of values obtained with filters and by direct measurements of mass distributions by Kihong Park; David B. Kittelson; Peter H. McMurry (1223-1230).
We compare measurements of aerosol mass concentrations obtained gravimetrically using Teflon coated glass fiber filters and by integrating mass distributions measured with the differential mobility analyzer–aerosol particle mass analyzer (DMA–APM) technique (Aerosol Sci. Technol. 36 (2002) 227). The DMA–APM technique measures the distribution of particle mass as a function of mobility size for particles of arbitrary shape and composition (Relationship between particle mass and mobility, and between aerodynamic and mobility size distributions for diesel exhaust particles, Environ. Sci. Technol., 2003). Because DMA–APM measurements are made on particles suspended in the air, data are not affected by volatilization or adsorption that can affect the accuracy of the filter measurements. We show that the average ratio of the filter to DMA–APM mass concentrations for laboratory-generated dioctyl sebacate (DOS) and sodium chloride (NaCl) aerosols is 1.14±0.28, and they are well correlated (R 2>0.97). For diesel exhaust aerosols from an engine operating at 75% load, the two techniques agreed well with the average ratio of 0.98±0.20. When the engine was operated at a low (10%) load, mass concentrations measured with the filter were 2.13±0.54 times higher than values measured with the DMA–APM. We believe that the higher filter loading may be due to the adsorption of condensable vapors, which are emitted at higher rates under low engine load conditions. Measurements in which the condensable organics were removed with a catalytic stripper show much better agreement between the filter and DMA–APM, which support the hypothesis that vapor adsorption leads to artificially high filter data for low-load measurements. We conclude that the DMA–APM technique can be used to evaluate the accuracy of filter samples that may be affected by sampling artifacts, and to measure mass distributions with high time resolution for sub-0.5 μm aerosols.
Snowpack and precipitation chemistry at high altitudes by George M Hidy (1231-1242).
As an observational scientist, James P. Lodge Jr. contributed to the knowledge of atmospheric chemistry significantly and in many ways. As far back as the 1960s, his achievements included organization and oversight of a national survey of precipitation chemistry. This paper recognizes his broad interest in precipitation, focusing on recent studies of snow chemistry in the high-elevation regimes. A brief overview of snow chemistry in the American Rocky Mountains is provided in the context of other snow chemistry studies in the United States, Europe, the Himalayas, and the polar ice-sheets. A comparison of major ion concentrations in snow and neighboring NADP wet deposition sites in the Rocky Mountains follows. These data are then put in perspective of the major ion concentrations observed in snow at different global locations. This comparison touches on the similarities and differences in ion concentrations in the mid-latitude sites and the Polar Regions. A case study is reviewed to identify specific sources of sulfur and nitrogen oxides affecting snow chemistry in the American Rockies. The survey closes with a brief discussion of potentially important recent observations of snowpack chemistry interactions with the troposphere, the hydrosphere and the lithosphere.
Keywords: Snow chemistry; Precipitation chemistry; High altitude geochemistry; Sulfur and nitrogen oxides;
Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition by Douglas A. Orsini; Yilin Ma; Amy Sullivan; Berko Sierau; Karsten Baumann; Rodney J. Weber (1243-1259).
An improved particle-into-liquid sampler (PILS) has proven successful in both ground-based and aircraft experiments for rapid measurements of soluble aerosol chemical composition. Major modifications made to the prototype PILS (Aerosol Sci. Technol. 35 (2001) 718) improve particle collection at higher sample flow (15–17 l min−1) while maintaining minimal sample dilution. Laboratory experiments using a fluorescent calibration aerosol aided in designing the present system and characterized the PILS collection efficiency as a function of particle size. Collection efficiency for particle diameters D p between 0.03 and 10 μm is greater than 97%. In addition, the instrument now samples at low pressures (0.3 atmosphere) necessary for airborne measurements up to approximately 8 km in altitude. An ion chromatograph (IC) is coupled to the PILS for direct on-line analysis of the collected sample (hence the name ‘PILS-IC’). Proper selection of columns and eluants allows for 3.5–4 min separation of 9 major inorganic species (Na+, NH4 +, K+, Ca2+, Mg2+, Cl−, NO3 −, NO2 −, SO4 2−), while acetate, formate, and oxalate, are also possible in 15 min. Any analytical technique capable of continuous online analysis of a liquid sample can be coupled to the PILS for quantitative semi-continuous measurements of aerosol composition. Changes made to the prototype are explained and data from a recent experiment are compared with standard integrated filter measurements.
Keywords: Particulate matter; PM2.5; Instrumentation; Ionic aerosol components; On-line analysis;
Organic anions in damage layers on monuments and buildings by Cristina Sabbioni; Nadia Ghedini; Alessandra Bonazza (1261-1269).
This article is focused on small (C1–C2) organic anions present in the damage layers on historic monuments and buildings. Formate, acetate and oxalate are consistently found in black crusts, where atmospheric deposition accumulates along with the products of the chemical transformation of stone and mortars. While sulphation processes affecting building materials have been extensively studied, the importance of carbon compounds in black crusts is only recently being realised. Recent data show carbon to be the second most important airborne element after sulphur in damage layers on building exteriors. Total carbon is composed of carbonate-, organic-, and elemental carbon. The organic fraction includes formate, acetate and oxalate; these are always detected in black crusts. Their origin, role and measurement in the atmosphere and in the museum environment have been the subject of many studies, but little has been reported concerning their presence in building exterior damage layers. This paper presents data on these anions in damage layers on stones and mortars sampled on monuments and buildings at different urban, suburban and rural European sites. Oxalate encountered in black crusts likely originates from the metabolism of micro-organisms and protective treatments on surfaces. Primary and secondary atmospheric pollutants are likely the main sources of formate and acetate anions.
Keywords: Damage; Black crusts; Formate; Acetate; Oxalate;
Measurements in support of air quality improvement—some historical insights by Roger L Tanner (1271-1276).
A brief historical summary of developments in a select few areas of atmospheric measurements is given to illustrate how they have led to an improvement in our ability to effect meaningful, effective control strategies by improving our knowledge of the atmospheric chemistry of trace gases and particles. Conversely, some examples will also be given of how measurement deficiencies led to misleading conclusions concerning the nature and extent of environmental pollution, and permitted the development of ineffective control strategies. Measurement artifacts for prominent particulate constituents—sulfate, nitrate and organic species—are discussed, focusing on key measurement principles that were developed to overcome those artifacts. The use of tracers and source apportionment techniques to quantify the contributions of sources of pollutants and their precursors is another example of measurement science enabling effective control strategies. The intent of this paper is to illustrate how better measurement science leads to more accurate assessment of pollutant formation and transport processes, and hence to the development of more effective pollutant control strategies.
Keywords: Measurement science; Control strategies; Measurement Artifact; Historical overview;
Semi-volatile secondary organic aerosol in urban atmospheres: meeting a measurement challenge by Delbert J. Eatough; Russell W. Long; William K. Modey; Norman L. Eatough (1277-1292).
Ammonium nitrate and semi-volatile organic compounds are significant components of fine particles in urban atmospheres. These components, however, are not properly determined with current US EPA accepted methods such as the PM2.5 FRM or other single filter samplers due to significant losses of semi-volatile material (SVM) from particles collected on the filter during sampling. Continuous PM2.5 mass measurements are attempted using methods such as the R&P TEOM monitor. This method, however, heats the sample to remove particle-bound water which also results in evaporation of SVM. Research at Brigham Young University has resulted in samplers for both the integrated and continuous measurement of total PM2.5, including the SVM. The PC-BOSS is a charcoal diffusion denuder based sampler for the determination of fine particulate chemical composition including the semi-volatile organic material. The RAMS is a modified TEOM monitor which includes diffusion denuders and Nafion dryers to remove gas phase material which can be absorbed by a charcoal sorbent filter. The RAMS then uses a “sandwich filter” consisting of a conventional particle collecting Teflon coated TX40 filter, followed by an activated charcoal sorbent filter which retains any semi-volatile ammonium nitrate or organic material lost from the particles collected on the TEOM monitor Teflon coated filter, thus allowing for determination of total PM2.5 mass including the SVM. Recent research conducted by Brigham Young University using these two samplers has indicated the following about semi-volatile organic aerosol:
Keywords: Organic aerosol; Semi-volatile organic material; Sampling artifacts; Denuder samplers; Urban fine particulate material;
Measurements of sulfur dioxide, ozone and ammonia concentrations in Asia, Africa, and South America using passive samplers by Gregory R Carmichael; Martin Ferm; Narisara Thongboonchoo; Jung-Hun Woo; L.Y Chan; Kentaro Murano; Pham Hung Viet; Carl Mossberg; Rajasekhlar Bala; Jariya Boonjawat; Pramote Upatum; Manju Mohan; Sharad P Adhikary; Arun B Shrestha; J.J Pienaar; Ernst B Brunke; Tai Chen; Tang Jie; Ding Guoan; Leong Chow Peng; Sri Dhiharto; Hery Harjanto; Aida M Jose; Wilson Kimani; Abdelmalek Kirouane; Jean-Pierre Lacaux; Sandrine Richard; Osvaldo Barturen; Jorge Carrasco Cerda; Augusto Athayde; Tania Tavares; Jose Silva Cotrina; Erdal Bilici (1293-1308).
Measurements of gaseous SO2, NH3, and O3 using IVL passive sampler technology were obtained during a pilot measurement program initiated as a key component of the newly established WMO/GAW Urban Research Meteorology and Environment (GURME) project. Monthly measurements were obtained at 50 stations in Asia, Africa, South America, and Europe. The median SO2 concentrations vary from a high of 13 ppb at Linan, China, to <0.03 ppb at four stations. At 30 of 50 regional stations, the observed median concentrations are <1 ppb. Median ammonia concentrations range from 20 ppb at Dhangadi, India, to <1 ppb at nine stations. At 27 of regional stations, the ambient ammonia levels exceed 1 ppb. The median ozone concentrations vary from a maximum of 45 ppb at Waliguan Mountain, China, to 8 ppb in Petit Saut, French Guiana. In general, the highest ozone values are found in the mid-latitudes, with the Northern hemisphere mid-latitude values exceeding the Southern hemisphere mid-latitude levels, and the lowest values are typically found in the tropical regions.
Keywords: Diffusive samplers; Sulfur dioxide; Ammonia; Ozone; Asia; Africa;
Evaluation of lower carbonyls and photochemical oxidants by HPLC-UV and HRGC-MS by Massimiliano Possanzini; Vincenzo Di Palo; Angelo Cecinato (1309-1316).
Formaldehyde, acetaldehyde, acetone, ozone and nitrogen dioxide were measured in ambient air after having simultaneously collected them on a pair of silica gel cartridges coated with 2,4-dinitro-phenylhydrazine (DNPH) and 1-methyl-1-(2,4-dinitro)-phenylhydrazine (MDNPH), respectively. By reaction with DNPH, the three carbonyls were derivatized to hydrazones and NO2 converted into 2,4-dinitrophenylazide (DNPA), whilst both NO2 and O3 produced N-methyl-2,4-dinitroaniline (MDNA) on MDNPH coating, which was also able to fast react with formaldehyde. The different derivatives were then separated, identified and quantified by HPLC-UV and HRGC-MS. The limits of detection (LOD) for O x (O3+NO2), NO2, HCHO, CH3CHO and CH3COCH3 were 1.5, 0.4, 0.7, 0.7 and 0.7 ppbv, respectively, for 30 l (1 h) air sampled. When compared with ozone photometric and nitrogen dioxide chemiluminescent analysers, the proposed chromatographic methods, especially HPLC, demonstrated good accuracy (14% for O x in the 20–100 ppbv range and 21% for NO2 in the 3–14 ppbv range) under field sampling conditions. The comparison between DNPH and MDNPH cartridges about lower carbonyls showed that only HCHO was efficiently collected on MDNPH cartridges, whilst CH3CHO and CH3COCH3 were partly and almost completely lost, respectively. However, significant differences in HCHO mixing ratios (39% on average) were observed with the two types of cartridges.
Keywords: Lower carbonyls; Oxidants; DNPH; MDNPH; Field measurements;
Similarities and differences in PM10 chemical source profiles for geological dust from the San Joaquin Valley, California by Judith C Chow; John G Watson; Lowell L Ashbaugh; Karen L Magliano (1317-1340).
A systematic sampling and analysis approach was followed to acquire chemical source profiles for six types of geological dust in California's San Joaquin Valley. Forty-seven samples from 37 locations included: (1) urban and rural paved roads, (2) residential and agricultural unpaved roads and parking areas, (3) almond, cotton, grape, safflower, and tomato fields, (4) dairy and feedlot surfaces, (5) salt-laden lake and irrigation canal drainage deposits, and (6) building and roadway construction/earthmoving soil. These samples were dried, sieved, resuspended, sampled through a PM10 inlet onto filters, and chemically analyzed to construct PM10 source profiles (fractional mass abundances and uncertainties) for 40 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Mo, Pd, Ag, Cd, In, Sn, Sb, Ba, La, Au, Hg, Tl, Pb, and U), 7 ions (Cl−, NO3 −, PO4 2−, SO4 2−, Na+, K+, and NH4 +), organic and elemental carbon (OC and EC), 8 carbon fractions (OC1, OC2, OC3, OC4, OP, EC1, EC2, and EC3), and carbonate carbon. Individual source profiles with analytical precisions were averaged and compared to quantify differences in chemical abundances for: (1) duplicate laboratory resuspension sampling, (2) multiple sampling within the same agricultural field, (3) sampling at different locations for the same land-use activity, (4) sampling of different activities regardless of location, and (5) grouping of different activities into generalized emission inventory source categories. Distinguishing features were found among composite source profiles of six source types. Elemental carbon and Pb marked paved road dust; Na+, Na, S, and SO4 2− marked salt deposits; OC, PO4 2−, P, K+, K, and Ca characterized animal husbandry; and several metals (Ti, V, Mn) marked construction soil, with abundances 2–10 times higher than those of other profiles. High-sensitivity X-ray fluorescence analysis resulted in detectable alkali and rare earth elements. Ga, Zr, Sn, and Ba were found in some of the paved road dust profiles; toxic species such as As, Mo, Cd, Sb, and U were found in salt deposits from canal drainage; and Pd, Rb, Sr, and Tl were found in construction dust. The profile-compositing methodology can be used for evaluating similarities and differences for other source characterization studies.
Keywords: Source profile; Geological dust; Paved and unpaved road dust; Agricultural soil;
Design and performance of a free-air exposure system to study long-term effects of ozone on grasslands by M Volk; M Geissmann; A Blatter; F Contat; J Fuhrer (1341-1350).
Studying long-term effects of ozone on perennial plant communities in situ is difficult because of the need for large observation plots and long exposure times, and because of confounding effects of altered microclimatic conditions in most systems. A novel free-air fumigation system was designed for multi-year exposures of semi-natural grassland plots to either ambient or elevated ozone concentrations at a Swiss sub-alpine site. The system operates by releasing ozone-enriched air from either one of two 120° sectors, placed in each of the two main wind directions. Ozone-enriched air is rapidly mixed with ambient air behind a small transparent windscreen mounted at canopy height around the 7-m diameter circular plots. Ozone generation and dispensing during daylight hours is PC controlled and depends upon wind speed, wind direction and ambient ozone. In 2001, from April to October fumigation was possible during 85% of the time. The ozone-enrichment factor (EF, [O3]enriched/[O3]control) in ozone plots relative to control plots averaged 1.48 (±0.24 SD), and EF was highest with winds of around 2 m s−1. The seasonal cumulative ozone exposure (AOT40) at canopy level was 5 ppm h in the control and 30 ppm h in the ozone-treated plots, with less than 10% variation between replicates, and 13 ppm h in ambient air at 2 m. Variation in ozone across the plot-diameter was <5% for 24-h mean concentrations, but differed by a maximum of 20% in terms of AOT40. There was no difference in microclimatic conditions between experimental plots and ambient conditions. It is concluded that the system is suitable for long-term ozone experiments at relatively low running costs, but that the variation in ozone distribution across the plots may lead to systematic differences in cumulative exposure over longer periods of time which need to be taken into account when relating exposure to biological effects.
Keywords: Ozone; Free-air ozone exposure system; Grassland;
Continuous wet denuder measurements of atmospheric nitric and nitrous acids during the 1999 Atlanta Supersite by Zhang Genfa; Sjaak Slanina; C Brad Boring; Piet A.C Jongejan; Purnendu K Dasgupta (1351-1364).
Two different measurement methods for atmospheric nitric and nitrous acid during the Atlanta Supersite study are described and compared. Both approaches combined wet denuder collection coupled to ion chromatographic analysis. One of these utilized a rotating wet annular denuder maintained indoor with a very dilute Na2CO3 solution as an absorber, operated by the Energieonderzoek Centrum Nederland (ECN), ion chromatography (IC) being conducted with a carbonate eluent system. Data from this instrument was available for a 15 min sample every hour. The other wet denuder was of the parallel plate design and was deployed on the roof of the measurement shelter. This device used dilute H2O2 solution as an absorber and was coupled to an IC operated with a hydroxide eluent. Operated by Texas Tech University (TTU), this instrument provided data with 10 min time resolution. When both instruments were seemingly operating properly, data from TTU and ECN instruments were well correlated, although the peak HNO3 values during high NO2/NO y periods were lower for the TTU instrument. Daily peaks in HNO3, typically ranging in magnitude between 3 and 6 ppbv (7.8 ppbv registered by the ECN instrument on the highest NO y day) were observed. HONO results from both TTU and ECN instruments exhibited strong diurnal variations with nighttime peaks up to ∼5 ppbv. Data from the middle of the study period for the two instruments were correlated with a r 2 value of 0.78. The relationship was not statistically distinguishable from a 1:1 correspondence. A similar correlation of r 2=0.76 was observed for the HNO3 data; in this case the peak concentrations occurring in day time.
The significance of secondary organic aerosol formation and growth in buildings: experimental and computational evidence by Golam Sarwar; Richard Corsi; David Allen; Charles Weschler (1365-1381).
Experiments were conducted in an 11 m3 environmental chamber to investigate secondary particles resulting from homogeneous reactions between ozone and α-pinene. Experimental results indicate that rapid fine particle growth occurs due to homogeneous reactions between ozone and α-pinene, and subsequent gas-to-particle partitioning of the products. A new indoor air quality model was used to predict dynamic particle mass concentrations based on detailed homogeneous chemical mechanisms and partitioning of semi-volatile products to particles. Chamber particle mass concentrations were estimated from measured particle size distributions and were in reasonable agreement with results predicted from the model. Both experimental and model results indicate that secondary particle mass concentrations increase substantially with lower air exchange rates. This is an interesting result, given a continuing trend toward more energy-efficient buildings. Secondary particle mass concentrations are also predicted to increase with lower indoor temperatures, higher outdoor ozone concentrations, higher outdoor particle concentrations, and higher indoor α-pinene emissions rates.
Keywords: Indoor chemistry; Ozone; Secondary particles; Terpenes; α-Pinene;
Integrating nephelometer measurements for the airborne fine particulate matter (PM2.5) mass concentrations by Arun D. Shendrikar; William K. Steinmetz (1383-1392).
This work describes the application of integrating nephelometer measurements for the determination of airborne fine particulate matter (PM2.5) mass concentrations.In response to over 150 complaints (spanning a period of 20 years) from local citizens of irritant fogs and pungent odors, the North Carolina Division of Air Quality conducted a monitoring program, in collaboration with the Washington Regional Air Quality Office and PCS Phosphate, Inc., to characterize air quality in the Pamlico River airshed of eastern North Carolina. The continuous monitoring from 1 May through 31 October 2000 at four sites, involved collection of air samples and subsequent quantification for reactive acidic and basic gases, aerosols and fine particulate matter (PM2.5) using a 7-day Annular Denuder System (ADS). Additionally, the airborne concentration of the fine particulate matter (PM2.5) was concurrently (to the ADS) monitored using a tapered element oscillating micro-balance (TEOM). Relevant meteorological data were obtained from conventional sensors installed at each sampling site. An integrating nephelometer was used for the regional visibility measurements.An integrating nephelometer was used to measure light scattering (a surrogate for visibility) continuously for 24-h per day over a 6-month period at the four sites. A linear relationship has been found for the nephelometer (Betascat) measurements and mass data (PM2.5) obtained both from the TEOM and ADS. The calculated correlation coefficient results between nephelometer and ADS and nephelometer and TEOM are satisfactory and close to one. This indicates that in this region, the nephelometer measurements have the potential to be a surrogate for the determination of regional airborne fine particle (PM2.5) mass concentrations. The ratios for each of the four sampling sites using 24-h averages of nephelometer data and PM2.5 concentrations from the ADS units and the TEOM gave an average ratio of 0.32±0.02. This value implies that the physical properties of the fine particulate (PM2.5) mass at each of the four sites were similar.The precision of nephelometer measurements (as Betascat) has been demonstrated by collocating three nepehlometers for continuous 24-h measurements for 10 days at one of the four sampling sites. Percent difference among the three instruments ranged from 0.42% to 4.41% and the inter-correlation produced R 2 values of 0.9833, 0.9874 and 0.9943, respectively.This study results demonstrates that the integrating nephelometer is a simple, inexpensive and a sensitive instrument that can be used in field studies. Furthermore, data on both light scattering (for visibility) and fine particulate (PM2.5) mass concentrations can be obtained reliably and importantly in a time effective manner for a rapid assessment of fine particle (PM2.5) air pollution.
Keywords: Integrating nephelometer; Light scattering; Weekly air pollution sampler; Tapered element oscillating micro-balance; Fine particulate matter;
Direct evidence for chlorine-enhanced urban ozone formation in Houston, Texas by Paul L Tanaka; Daniel D Riemer; Sunghye Chang; Greg Yarwood; Elena C McDonald-Buller; Eric C Apel; John J Orlando; Philip J Silva; Jose L Jimenez; Manjula R Canagaratna; James D Neece; C.Buddie Mullins; David T Allen (1393-1400).
Urban air pollution is characterized by high ozone levels, formed when volatile organic compounds (VOCs) are oxidized in the presence of nitrogen oxides (NO x ). VOC and NO x emissions controls have traditionally been implemented to reduce urban ozone formation, however, a separate chemical species implicated in ozone formation in Houston, TX and possibly other urban areas is the chlorine radical (Cl·). Cl· enhances tropospheric VOC oxidation, but is not included in models used to develop air quality attainment plans. We present results of a three-fold approach to elucidate the importance of Cl· in urban ozone formation: (1) the first direct evidence of chlorine chemistry in the urban troposphere, (2) enhanced ozone formation (>75 parts per 109 (ppb/h) observed when small amounts of chlorine (Cl2) are injected into captive ambient air, and (3) enhanced ozone formation (∼16 ppb) predicted by regional photochemical models employing Cl· chemistry. These results suggest that reducing chlorine emissions should be considered in urban ozone management strategies.
Keywords: Air quality; Captive air experiments; Regional photochemical modeling; Secondary aerosol chloride; Chloromethylbutenone;
Analysis of dust storms observed in Mongolia during 1937–1999 by L Natsagdorj; D Jugder; Y.S Chung (1401-1411).
Climatology of dust storms in Mongolia is compiled based on observational data of 49 meteorological stations from 1960 to 1999 and compared them with data between 1937 and 1989. Three different maps of the distribution of dust storms, drifting dust and the number of dusty days are presented. The results of the analysis show that the number of days with dust storms is <5 days over the Altai, the Khangai and the Khentei mountainous regions and more than 20–37 days in the Gobi Desert and semi-desert area. The greatest occurrence of drifting dust arises around the Mongol Els area of west Mongolia.The number of dusty days, which is derived from the sum of the number of days with dust storms and drifting dust, is <10 days in the mountainous area and 61–127 days in the Gobi Desert and the Great Lakes hollow of west Mongolia.It is found that 61% of dust storms occur in the spring in Mongolia and a dust storm lasts on average from 3.1 to 6.0 h. About 65.5–91.0% of dust storms occur in daytime and 9.0–34.5% at night. Dust storms occur more frequently in the city region and are accompanied by surface wind speeds usually from 6 to 20 ms−1. Dust storms usually occur when soil and air are dry, and 70% of dust storms occur in dry soil conditions. When dust storms occur, relative humidity averages 20–40% in Mongolia.An important outcome of this study is the trend of dusty days between 1960 and 1999. It shows that the number of dusty days has tripled from the 1960s to 1990s and has decreased since 1990.
Keywords: Dusty days in Mongolia; Dust storm climatology; Reddish brown sand; Sand storms; Source information of dust storms;