Atmospheric Environment (v.36, #38)

Molecular composition of organic fine particulate matter in Houston, TX by M.P. Fraser; Z.W. Yue; R.J. Tropp; S.D. Kohl; J.C. Chow (5751-5758).
Organic fine particulate matter collected in Houston, TX between March 1997 and March 1998 was analyzed to determine the concentration of individual organic compounds. Samples from four sites were analyzed including two industrial locations (Houston Regional Monitoring Corporation (HRM-3) site in Channelview and Clinton Drive site near the Ship Channel Turning Basin), one suburban location (Bingle Drive site in Northwest Houston) and one background site (Galveston Island). At the three urban locations, samples were divided into three seasonal sample aggregates (spring, summer and winter), while at the background site a single annual average sample pool was used. Between 10 and 16 individual samples were pooled to get aggregate samples with enough organic carbon mass for analysis. Overall, 82 individual organic compounds were quantified. These include molecular markers which are compounds unique to specific fine particle sources and can be used to track the relative contribution of source emissions to ambient fine particle levels. The differences both spatially and temporally in these tracers can be used to evaluate the variability in emission source strengths.
Keywords: PM2.5 composition; Organic speciation; Molecular markers;

As the fundamental building block of the emissions estimation process, a driving cycle needs to be representative of real-world driving behavior. The driving cycle construction method becomes crucial for generating a representative driving cycle. In this paper, we revisit the Unified Cycle's (i.e., the LA92 driving cycle) construction method. The California Air Resources Board's Unified Cycle used a “microtrips” approach, a speed–acceleration frequency distribution plot, and a quasi-random selection mechanism to build the driving cycle. There is concern that the Unified Cycle does not reflect the true driving patterns due to the identified flaws in the construction methodology. Treating a driving trace as a stochastic process, we construct a new driving cycle (LA01) with the same driving data originally used to build the Unified Cycle. We then compare the two driving cycles with the sample data set with respect to the durations and intensities of the modal events. The new driving cycle is found to better replicate the modal events observed in the sample data. A comparison of average road power values between the sample data, LA01, and the Unified Cycle also confirms the effect of fine-scale driving on emissions. These differences result from the different construction approaches and can be expected to affect emissions inventory estimation.
Keywords: Driving cycle; Microtrips; Modal events; Transition probability; Emissions inventory;

The relationship between near-surface ozone concentration and the structure of the nocturnal boundary layer was investigated during a field campaign conducted in 1998 in the Lower Fraser Valley (LFV), British Columbia Canada. Despite the spatial and temporal variation in frequency and morphology, secondary nocturnal ozone maxima were shown to be an important feature of the diurnal ozone cycle throughout the LFV, and localised increases in ozone occasionally exceeded more than half the previous day's maximum concentration.Turbulence in the nocturnal boundary layer was shown to be weak and intermittent. Vertical profiles of Richardson number and ozone concentration indicated that the temporary turbulent coupling of the residual layer to the surface layer facilitated the transport of ozone stored aloft to the surface. Despite the overall complexity of the system, results show that seven out of the 19 ozone spikes observed at the Aldergrove site coincided with turbulence associated with the development of the down-valley wind system. A further nine spikes occurred during periods when a low-level jet was identified aloft. Significantly, ozone concentrations were shown to be highly variable in the residual layer and played an important role in determining the morphology of secondary ozone maxima at the surface. Largest increases in surface ozone concentration occurred when turbulence coincided with periods when ozone concentrations in excess of 80 ppb were observed aloft.
Keywords: Low-level jet; Residual layer; Vertical mixing; Turbulence; Mesoscale flows;

To characterize atmospheric nitrogen deposition to Barnegat Bay, measurements of nitrate and ammonium were made, both in precipitation and in aerosol particulate matter, at coastal Tuckerton in southern New Jersey from February 1999 to February 2001. Results show that the concentrations of nitrate and ammonium in the ambient air exhibit strong temporal variation. The concentrations in precipitation ranged from 2.26 to 84.6 μmol l−1 (mean: 29.1 μmol l−1) for nitrate and from 0.625 to 107 μmol l−1 (mean: 18.3 μmol l−1) for ammonium. Most of the pH values in precipitation fall below 4.5, suggesting an acidic nature for precipitation. The low spring-time mean δ 15N values in rain for both ammonium (−4.6‰) and nitrate (−6.03‰) indicate that increased agricultural and soil emissions as well as anthropogenic emissions contribute to atmospheric nitrate and ammonium. The average concentrations in the aerosol phase were 2.04 μg m−3 for nitrate and 0.497 μg m−3 for ammonium. High concentrations of aerosol nitrate were associated with both submicrometer and supermicrometer particles, while aerosol ammonium was primarily concentrated on particles of ∼0.5 μm in diameter. High wet deposition rates of nitrate and ammonium were observed during the summer in both 1999 and 2000, with average summer-time rates of ∼4.12 mmol m−2  month−1 for nitrate and 3.18 mmol m−2  month−1 for ammonium. On an annual basis, the total atmospheric deposition rates were 32.9 mmol m−2  yr−1 for nitrate and 20.3 mmol m−2  yr−1 for ammonium, and wet deposition accounted for >88% of the total deposition. The annual atmospheric input to the Barnegat Bay ecosystem is estimated to be 9.2×106  mol yr−1 for nitrate and 5.7×106  mol yr−1 for ammonium.
Keywords: Deposition fluxes; Atmospheric nitrate and ammonium; Coastal marine atmosphere; Precipitation; Aerosol particles;

Continuous measurements were taken during a 22-day campaign held in the summer of 2000 at a site close to the Great Smoky Mountains National Park in eastern Tennessee. The campaign was conducted to investigate the relationships between ultrafine/fine particles and gaseous species observed. A varimax-rotation factor analysis was performed to explore the relationship of the fine and ultrafine particle number concentrations, the gaseous species concentration, the mean wind speed, and the solar radiation. A 6-factor model was found to best resolve 79.7% of the variability embedded in the data. The model suggests that 31.4% of the data variability could be explained by ultrafine particles (the diameters smaller than or equal to 100 nm). It was difficult to label this factor without chemistry information of the ultrafine particles. However, no gas species were loaded on Factor 1 indicating the ultrafine particles observed in this study were not associated with primary source emissions. The decoupling of the ultrafine particles from the fine particles also implies that the former ones might have been produced and transported to the site by separated mechanisms from those of fine particles. The second factor included the PM2.5 mass concentration and the number concentrations of particles in the diameter range of 101–400 nm. The loading pattern on Factor 2 led to the conclusion that this factor was contributed by regional transport. The third factor includes CO, NO2, reactive odd nitrogen (NO y ), and SO2 that were contributed by primary source emissions. The mean wind speed and ozone were loaded in Factor 4 that was labeled as ozone transport. Identification of this factor led to an observation that ozone transport to the site was essentially decoupled from the regional transport factor of fine particles (i.e., Factor 2). Solar radiation was singly included in the fifth factor indicating this is a unique factor. The quality of NO data was marginal and the variable was distilled by the model into Factor 6. A multiple regression analysis further indicated that PM2.5 mass concentration was best explained by CO, O3, and number concentrations of particles in the diameter range between 0.1 and 0.4 μm. We also identified two unique events during the campaign in which the number concentrations of 31–51 nm particles dramatically increased by a factor of 10 in 30 min, reaching 40,000 cm−3 and lasting for a couple of hours. Particles in the size range just below and above those in the 31–51 nm diameter range also exhibited increases during these events, but the changes were much less dramatic.
Keywords: The Great Smoky Mountains National Park; Factor analysis; Ultrafine and fine particles; Source–receptor relationships;

Characterization of organic aerosol in Big Bend National Park, Texas by Steven G Brown; Pierre Herckes; Lowell Ashbaugh; Michael P Hannigan; Sonia M Kreidenweis; Jeffrey L Collett Jr (5807-5818).
The Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study was conducted in Big Bend National Park, Texas, July through October 1999. Daily PM2.5 organic aerosol samples were collected on pre-fired quartz fiber filters. Daily concentrations were too low for detailed organic analysis by gas chromatography-mass spectrometry (GC-MS) and were grouped based on their air mass trajectories. A total of 12 composites, each containing 3–10 daily samples, were analyzed. Alkane carbon preference indices suggest primary biogenic emissions were small contributors to primary PM2.5 organic matter (OM) during the first 3 months, while in October air masses advecting from the north and south were more strongly influenced by biogenic sources. A series of trace organic compounds previously shown to serve as particle phase tracers for various carbonaceous aerosol source types were examined. Molecular tracer species were generally at or below detection limits, except for the wood smoke tracer levoglucosan in one composite, so maximum possible source influences were calculated using the detection limit as an upper bound to the tracer concentration. Wood smoke was found not to contribute significantly to PM2.5 OM, with contributions for most samples at <1% of the total organic particulate matter. Vehicular exhaust also appeared to make only minor contributions, with maximum possible influences calculated to be 1–4% of PM2.5 OM. Several factors indicate that secondary organic aerosol formation was important throughout the study, and may have significantly altered the molecular composition of the aerosol during transport.
Keywords: Organic aerosol; BRAVO; Source apportionment; Visibility;

A biogenic emissions model for isoprene, monoterpenes, and nitric oxide has been developed with algorithms that rely on normalized difference vegetative index values derived from satellite remote sensing data to infer leaf area index. The model obtains emission factors from the Biogenic Emission Inventory System (BEIS). This biogenic emissions model, combined with a dry deposition model, was applied with environmental variable values supplied by MM5 (the fifth-generation Mesoscale Model). The modeled temporal variations and spatial distributions of the surface emissions rates of isoprene, monoterpenes, and nitric oxide the eastern US agreed well with reported simulations, measurements, and inferences. Use of the satellite data generates considerable detail in the spatial patterns, high temporal resolution, and a smooth seasonal variation in the emission rates. The new biogenic emissions model was used with a photochemistry modeling system to infer ozone (O3) concentrations in the lower troposphere above the eastern United States for a two-day case in July 1995, which had O3 episodes studied previously by the Ozone Transport Assessment Group. Compared to the results from the OTAG application of BEIS2, the satellite-data-derived isoprene emissions were slightly lower in the northeastern United States, which resulted in smaller values of O3 concentration and were 3–4 times higher in southeastern mixed forests, which had little impact on O3 except near strong NO x emission sources.
Keywords: Biogenic emissions; Remote sensing; Isoprene; Ozone; Modeling;

This study examined commuter exposure to respirable suspended particulate (PM10 and PM2.5) and carbon monoxide (CO) in public transportation modes in Guangzhou, China. During the sampling period, a total of 80 CO, 80 PM10 and 56 PM2.5 samples were conducted in four popular commuting modes (subway, air-conditioned bus, non-air-conditioned bus and taxi) while running in typical urban routes. The results show that the PM10 as well as CO level is greatly influenced by the mode of transport. The highest mean PM10 and CO level was obtained in a non-air-conditioned bus (203  μg m −3) and in an air-conditioned taxi (28.7  ppm), respectively. Noticeably, the exposure levels in subway are lower than those in the roadway transports. The ventilation condition of the transport is also a crucial factor affecting the in-vehicle level. There was statistically significant difference of PM 10  (p<0.01) and CO (p<0.01) level in taxi and PM 10  (p<0.01) level in bus between natural and mechanical ventilation. In this study, the effect of driving time has minor impact on the in-vehicle level. The exposure levels were only slightly lower in afternoon non-peak hour than in evening peak hour. This is related to the fact that the road traffic in the selected urban routes is dominated by the extensive use of public transports, which provide service at regular intervals regardless of the time of day. The PM2.5 inter-microenvironment variation is similar to the pattern of PM10. The PM2.5 to PM10 ratio in the transports was high, ranging from 76% to 83%. The poor vehicle emission controls, poor vehicle maintenance, plus the slow moving traffic condition with frequent stops are believed to be the major causes of high in-vehicle levels in some public commuting trips.
Keywords: Public transportation modes; PM10; PM2.5; CO; Commuter exposure;

Ambient concentrations and dry deposition fluxes of trace elements in Izmir, Turkey by Mustafa Odabasi; Aysen Muezzinoglu; Ayse Bozlaker (5841-5851).
Dry deposition samples were collected using a smooth surrogate surface at the Kaynaklar Campus of the Dokuz Eylul University in Izmir, Turkey. Concurrently ambient aerosol samples were collected. All samples were analyzed for anthropogenic and crustal trace elements. The average trace element concentrations and fluxes measured in this study were generally higher than those reported previously for urban and rural areas. The contribution of local terrestrial and anthropogenic sources were also investigated using enrichment factors (EFs) calculated relative to the local soil. Relatively lower EFs for ambient samples and high ambient concentrations indicated that the local soil was polluted and contributed significantly to ambient trace element concentrations. Deposition samples had higher EFs than the air samples. The EF sequences of trace elements were also different for deposition and ambient samples, probably due to the fact they have different mass median diameters and deposition velocities. The overall dry deposition velocities for trace elements calculated by dividing the particulate fluxes measured with the surrogate surfaces by ambient concentrations ranged from 0.6 (Al) to 6.2 cm s−1 (Fe). The agreement between the experimental dry deposition velocities determined in this study and the previously reported ones using similar techniques for trace elements was good.
Keywords: Dry deposition; Trace elements; Airborne heavy metals; Enrichment factors; Deposition velocity; Air pollution in Izmir;

Seasonal variation of ionic species in fine particles at Qingdao, China by Min Hu; Ling-Yan He; Yuan-Hang Zhang; Min Wang; Yong Pyo Kim; K.C. Moon (5853-5859).
Totally nine measurement campaigns for ambient particles and SO2 have been conducted during the period of 1997–2000 in Qingdao in order to understand the characteristics of the particulate matter in coastal areas of China. The mass fractions of PM2.5, PM2.5−10 and PM>10 in TSP are 49%, 25% and 26%, respectively. The size distribution of particles mass concentrations in Qingdao shows bi-modal distribution. Mass fraction percentages of water-soluble ions in PM2.5, PM2.5−10 and PM>10 decreased from 62% to 35% and 21%. In fine particles, sulfate, nitrate and ammonium, secondary formed compounds, are major components, totally accounting for 50% of PM2.5 mass concentration.The ratios of sulfate, chloride, ammonium and potassium in PM2.5 for heating versus non-heating periods are 1.34, 1.80, 1.56 and 1.44, respectively. The ratio of nitrate is 3.02 and this high ratio could be caused by reduced volatilization at lower temperature. Sulfate concentrations are higher than nitrate in PM2.5. The chemical forms of sulfate and nitrate are probably (NH4)2SO4 and NH4NO3 and chloride depletion was observed.Backward trajectory analysis reflected possible influence of air pollutant transport to Qingdao local aerosol pollution.
Keywords: Fine particles; Water-soluble ions; Sulfur dioxide; Mass size distribution; Seasonal variation;

Influence of African dust on the levels of atmospheric particulates in the Canary Islands air quality network by M Viana; X Querol; A Alastuey; E Cuevas; S Rodrı́guez (5861-5875).
Time series of levels of atmospheric particulate matter (TSP and PM10) were studied at 19 air quality monitoring stations in the islands of Tenerife and Gran Canaria (Canary Islands) during the period 1998–2000. After analysing seasonal variations, attention was focused on the detection of high TSP and PM10 events and on the identification of their natural or anthropogenic origins. Back-trajectory analysis and TOMS-NASA aerosol index as well as satellite imagery (SeaWIFS-NASA) were used to identify three types of African dust outbreaks differing in seasonal occurrence, source origin and impact on TSP/PM10 levels. Mean annual and daily TSP and PM10 levels were compared with the forthcoming limit values of the EU Air Quality Directive EC/30/1999, and the results showed that the annual and daily limit values established for 2010 would only be met at rural stations. PM levels at urban background, urban and industrial sites would exceed the 2010 objectives. Only the levels at the urban-background stations would meet the requirements for 2005 despite the fact that the trade winds result in lower levels of atmospheric pollutants in the Canary Islands than in continental environments. The results highlight the role of African dust contributions when implementing the limit values of the EU directive.
Keywords: PM10; TSP; Saharan dust; Air quality monitoring; Canary Islands;