Particulate Matter Loading Research Articles

Monitoring Ambient Nitrate Radical by Open-Path Cavity-Enhanced Absorption Spectroscopy.

We describe an open-path cavity-enhanced absorption spectroscopy (OP-CEAS) technique for the ambient measurement of nitrate radicals (NO3) near 662 nm. Compared with the closed type of CEAS system with a sampling line, the OP-CEAS features high accuracy due to the lack of NO3 loss in the sampling line and cavity. On the basis of a 0.84 m long open-path cavity, the effective absorption length of ∼5 km is achieved by mirrors with a reflectivity of 0.99985 at 662 nm. The detection limit of OP-CEAS for the measurement of NO3 is 3.0 pptv (2σ) in 30 s, and the uncertainty is 11-15%. The instrument was successfully applied in a field measurement under low particulate matter (PM) loading conditions. As the sensitivity would be decreased due to strong PM extinction under heavy PM pollution conditions, we highlight the feasibility of this OP-CEAS configuration for field application in clean and moderate PM condition, such as forested regions affected by anthropogenic emissions. This technique is also appropriate for the field detection of other reactive trace gases in future studies.

Urban airborne particle exposure impairs human lung and blood Mycobacterium tuberculosis immunity

RationaleAssociations between urban (outdoor) airborne particulate matter (PM) exposure and TB and potential biological mechanisms are poorly explored.ObjectivesTo examine whether in vivo exposure to urban outdoor PM in Mexico City...

The use of hollow fiber dialysis filters operated in axial flow mode for recovery of microorganisms in large volume water samples with high loadings of particulate matter

Ultrafiltration concentration of microorganisms in large volume water samples containing high levels of particulate matter was evaluated in a proof of concept study. The organisms tested were Bacillus atrophaeus subspecies globigii spores and MS2 bacteriophage. To produce the large volume samples, fresh water sediment of a known particle size was added to 51 l of tap water. Five different concentrations of particulate matter were studied: 0, 50, 100, 150 and 750 mg solids/l. The concentration procedure used a dialysis filter as the ultrafilter configured for axial flow, either with or without recirculation. The target number of organisms spiked was 1 × 105 of either spores or bacteriophage per 51 l. After concentration, the filters were dissected to retrieve the fibers which were then washed using surfactant solution which was then analyzed for the target organisms. Two washes of the filter fibers were carried out sequentially. For axial flow with recirculation, the first wash produced statistically greater recovery of B. globigii spores (26–40% of spike) compared to the second wash (8–13% of spike). Total recovery (the sum of the recoveries for the first and second washes) ranged from 35 to 53%. Recovery increased as the solids level increased from 0 to 150 mg solids/l. Recovery at the 100 and 150 mg solids/L loadings was statistically higher at the P < .05 level than recovery at 0 mg/L solids. At 150 mg solids/L, axial flow without recirculation (dead end) yielded lower recovery than axial flow with recirculation, however the difference was not significant at the P < .05 level. Recovery of B. globigii at 750 mg solids/L averaged 38% using dead end axial flow. The average recovery of MS2 bacteriophage was 45% at a solids concentration of 150 mg/L using axial flow with recirculation. PhiX174 and Phi8 were also studied, however these bacteriophage appeared to be inactivated in the matrix of concentrated wash water. One hundred liters of water containing 750 mg solids/L was concentrated using dead end axial flow, and only minimal problems with filter clogging were observed. Results described herein suggest axial flow ultrafiltration is an effective concentration method for microorganisms in water containing high levels of particulate matter.

Assessment of source profiles for suspended particulate pollutants in Ibadan, Nigeria using positive matrix factorization

Positive Matrix Factorization receptor model developed by the United States Environmental Protection Agency known as EPA PMF receptor model and reconstructed mass model were applied to air pollution data collected over Ibadan south west Nigeria. The essence was to determine the source profiles responsible for the high pollution level of Ibadan and to compare the sources resolved by these two methods. Particulate matter load was sampled over Ibadan, southwest Nigeria with the aid of low volume Gent air sampler, equipped with the Norwegian Institute for Air Research (NILU) Stacked Filter Unit (SFU). Two separate 47-mm nuclepore filters were mounted on the SFU to collect both fine and coarse particulates separately. Trace elements were determined using instrumental neutron activation analysis (INAA) and energy dispersive x-ray fluorescence (EDXRF) spectrometry. Five factors were resolved each for both fine and coarse fractions using EPA PMF. For the fine fraction, soil dust, vehicular emission, oil combustion, open burning and copper-rich source were the major sources of fine particulates over Ibadan city contributing 42, 16, 10, 22 and 10% respectively to the total aerosol loading over Ibadan. Vehicular emission, continental soil, sea salt, locally generated dust and copper-rich source were the sources identified for the coarse particulates. These contributed 7, 49, 13, 23 and 8% respectively. It was observed that emission from open burning was very high (22%), being the second largest contributor to the fine particulates. Reconstructed mass model showed good agreement with PMF in implicating soil dust as the major contributor of airborne pollutants over Ibadan. There was good correlation between the reconstructed mass and the measured mass with r 2 values of 0.87 and 0.98 for fine and coarse particulates respectively. The result of this work showed that re-suspended soil particulates were the major constituents of airborne particulate matter over Ibadan, with over 70 % contribution to the coarse mass and over 40 % contribution to the fine mass. Keywords: Particulate Matter, Reconstructed mass, Refuse burning, PMF, Receptor model, Composite Variables

An inclusive view of Saharan dust advections to Italy and the Central Mediterranean

We address observations of physical and chemical properties of Saharan dust advections (SDA) as observed in the Central Mediterranean basin, within the framework of the LIFE+10, DIAPASON project (www.diapason-life.eu). DIAPASON aimed at the definition of best practices and tools to detect and evaluate the contribution of Saharan dust to ground particulate matter (PM) loads. Polarization-sensitive, automated lidar-ceilometers (PLC) are one of the tools prototyped and used in the Rome area to reach this goal. The results presented in this study focus on: 1) the effectiveness of various observational tools at detecting and characterizing atmospheric dust plumes, and 2) processes and properties of Saharan dust advections reaching the central Mediterranean region. In this respect, the combination of numerical model forecasts and time-resolved (at least hourly) PLC or chemical observations was found to constitute an efficient way to predict and confirm the presence of Saharan dust. In the period 2011–2014, Saharan dust advections were observed to reach over Rome on about 32% of the days. In some 70% of these days the dust reached the ground in dry conditions, while 30% of advection days involved wet deposition. Dry (wet) deposition was found to maximize (minimize) in summer. The northern Sahara between Algeria and Tunisia (Grand Erg Oriental), was confirmed as the most frequent region of origin of the dust mobilized towards central Italy. Secondary source regions include northern Morocco and Libya. On a statistical basis, Saharan advections to Rome were preceded by increasing atmospheric pressure and stability. These conditions were found to favor the accumulation of aerosols related to local emission sources before the SDA reached the ground. Meteorology (precipitation and turbulence in primis) resulted to be an important modulator of PM concentrations during SDAs. Magnitude and timing of these factors should be well considered to correctly evaluate the dust share in PM loads or the related health effects. Saharan advections observed during DIAPASON affected particle concentrations down to diameters of about 0.6–1 μm, with number concentrations peaking at the 2.5 μm diameter range. These advections were associated with a significant increase in Si-rich particles containing a non-negligible fraction of water. Rainfall was observed to preferentially remove dust particles larger than 2 μm, causing a significant depletion in the Ca-rich fraction with respect to the Si-rich one. The increase in PLC depolarization ratios above 5%, as well as the hourly PIXE records of the Si/Ca ratio increasing above 1 were found to represent good markers for the actual presence of Saharan dust particulate matter, when Saharan advection conditions are occurring.

Source Identification of Episodic Rain Pollutants by New Approach: Combining Satellite Observations and Backward Air Mass Trajectories

ABSTRACT In this study, various source apportionment methods, viz., enrichment factor, relative source contribution, and factor analysis in addition to cluster analysis coupled with satellite observations, were used to investigate the origin of rainwater pollutants in an arid urban area of Saudi Arabia. The rainwater samples were collected by an automatic wet-only sequential rain sampler and analyzed for their pH, electrical conductivity (EC), and major ions (Cl–, NO3–, SO42–, HCO3–, Na+, K+, NH4+, Ca2+, and Mg2+). The results revealed that the chemical composition was dominated by Ca2+, SO42–, Cl–, HCO3–, and Na+, which represented 80% of the total ionic equivalent concentration. Ca2+, the most abundant ion, exhibited a mean concentration of 480 µeq L–1 and accounted for 30% of the total ionic equivalent concentration. The study area received a total ionic wet deposition flux (FWD) of 4.07 tons km–2 y–1, and SO42– and NO3– contributed 76% and 24%, respectively, of the rainwater acidity. Ca2+ was responsible for 80% of the rainwater’s neutralization. The source apportionment indicated that intense local human activity and medium- to long-range transport from Kuwait, Iraq, Qatar, Riyadh, and the Western Province produced the majority of the anthropogenic components (SO42–, NO3–, and NH4+), which represented 47% of the total ionic FWD. However, moderate to high particulate matter loads over the southern part of Saudi Arabia and long-range transport from Iraq and Kuwait contributed the crustal components (Ca2+, HCO3–, K+, and Mg2+), which accounted for 36% of the total ionic FWD, whereas the Arabian Gulf was the primary source of the marine components (Na+ and Cl–). We found combining satellite observations and cluster analysis of backward air mass trajectories to be an effective new approach for assessing the source-receptor relationships for atmospheric air pollutants.

Analysis of abrupt changes in the PM2.5 concentration in Beijing during the conversion period from the summer to winter half-year in 2006–2015

Beijing has experienced increasingly frequent heavy air pollution caused by high loadings of fine particulate matter (PM2.5) in recent decades, especially in autumn and winter. In this study, the formation mechanisms of air pollution episodes between late September and early October were investigated on the basis of observations and reanalysis data from 2006 to 2015. During the transitional period from the East Asian summer monsoon (EASM) to the East Asian winter monsoon (EAWM), an abrupt change in meteorological conditions resulting in heavy PM2.5 pollution episodes was regularly observed in autumn (around October 4–5). Thereafter, pollution episodes with higher PM2.5 concentrations and more frequent and longer duration occurred after October 4–5. In particular, another marked increase in the PM2.5 concentration occurred around mid-November when city heat supply began. We applied the moving t-test (MTT) and Mann–Kendall (MK) methods to investigate the role of meteorological factors affected by the Asian monsoon. The abrupt change in the PM2.5 concentration in autumn (around October 5) was closely related to the monsoon transition, during which the atmospheric circulation and diffusion conditions were undergoing a transition from summer to winter type. This could be favorable for the transport, accumulation and secondary formation of PM2.5. The PM2.5 concentration increased obviously around November 15, and it could be caused by the combination of more emissions from city heat supply and the more stable winter atmosphere. This study revealed significant differences between the two mechanisms that produced increases in the PM2.5 concentration in autumn and winter, and indicated close connections between the variation of monsoon type and air pollution characteristics to some extent. When considering emission reductions, attention could also be given to the monsoon transition period when the atmospheric circulation pattern and diffusion conditions begin to change.

Study on Oxidation Activity of CuCeZrOx Doped with K for Diesel Engine Particles in NO/O2

CuCeZrOx and KCuCeZrOx catalysts were synthesized and coated on the blank diesel particulate filter (DPF) substrate and a particulate matter (PM) loading apparatus was used for soot loading. The catalytic performances of soot oxidation were evaluated by temperature programmed combustion (TPC) test and characterization tests were conducted to investigate the physicochemical properties of the catalysts. The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy. The results demonstrated that CuCeZrOx catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu0.9Ce0.05Zr0.05Ox over which the maximum soot oxidation rate decreased to 410 °C. Characterization tests have shown that catalysts containing 90% Cu have uniformly distributed grains and small particle sizes, which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot. The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K. The maximum particle oxidation rate can be easily realized at such a low temperature as 347°C.

Airborne particulate matter monitoring in Kenya using calibrated low-cost sensors

Abstract. East African countries face an increasing threat from poor air quality stemming from rapid urbanization, population growth, and a steep rise in fuel use and motorization rates. With few air quality monitoring systems available, this study provides much needed high temporal resolution data to investigate the concentrations of particulate matter (PM) air pollution in Kenya. Calibrated low-cost optical particle counters (OPCs) were deployed in Kenya in three locations: two in the capital Nairobi and one in a rural location in the outskirts of Nanyuki, which is upwind of Nairobi. The two Nairobi sites consist of an urban background site and a roadside site. The instruments were composed of an AlphaSense OPC-N2 ran with a Raspberry Pi low-cost microcomputer, packaged in a weather-proof box. Measurements were conducted over a 2-month period (February–March 2017) with an intensive study period when all measurements were active at all sites lasting 2 weeks. When collocated, the three OPC-N2 instruments demonstrated good inter-instrument precision with a coefficient of variance of 8.8±2.0 % in the fine particle fraction (PM2.5). The low-cost sensors had an absolute PM mass concentration calibration using a collocated gravimetric measurement at the urban background site in Nairobi.The mean daily PM1 mass concentration measured at the urban roadside, urban background and rural background sites were 23.9, 16.1 and 8.8 µg m−3, respectively. The mean daily PM2.5 mass concentration measured at the urban roadside, urban background and rural background sites were 36.6, 24.8 and 13.0 µg m−3, respectively. The mean daily PM10 mass concentration measured at the urban roadside, urban background and rural background sites were 93.7, 53.0 and 19.5 µg m−3, respectively. The urban measurements in Nairobi showed that PM concentrations regularly exceed WHO guidelines in both the PM10 and PM2.5 size ranges. Following a Lenschow-type approach we can estimate the urban and roadside increments that are applicable to Nairobi (Lenschow et al., 2001). The median urban increment is 33.1 µg m−3 and the median roadside increment is 43.3 µg m−3 for PM2.5. For PM1, the median urban increment is 4.7 µg m−3 and the median roadside increment is 12.6 µg m−3. These increments highlight the importance of both the urban and roadside increments to urban air pollution in Nairobi.A clear diurnal behaviour in PM mass concentration was observed at both urban sites, which peaks during the morning and evening Nairobi rush hours; this was consistent with the high roadside increment indicating that vehicular traffic is a dominant source of PM in the city, accounting for approximately 48.1 %, 47.5 % and 57.2 % of the total PM loading in the PM10, PM2.5 and PM1 size ranges, respectively. Collocated meteorological measurements at the urban sites were collected, allowing for an understanding of the location of major sources of particulate matter at the two sites. The potential problems of using low-cost sensors for PM measurement without gravimetric calibration available at all sites are discussed.This study shows that calibrated low-cost sensors can be successfully used to measure air pollution in cities like Nairobi. It demonstrates that low-cost sensors could be used to create an affordable and reliable network to monitor air quality in cities.

Planktonic prokaryote and protist communities in a submarine canyon system in the Ligurian Sea (NW Mediterranean)

Submarine canyons are large geomorphological features that incise continental margins and act as highly dynamic conduits of sediments from shallow to the deep-sea regions. They are often regarded as biodiversity and biomass hotspots, but their role in influencing plankton communities is still poorly known. We studied the ecology of planktonic deep-sea microbes in a submarine canyon system (Polcevera and Bisagno canyons) in the Ligurian Sea (NW Mediterranean Sea), aiming at testing whether these large-scale incisions are peculiar systems, in comparison to the overlying water and the adjacent uncarved slope, in terms of biogeochemical and biological features. We analysed microbial communities’ composition by high-throughput sequencing of 16S and 18S rRNA genes and their functional attributes by measuring heterotrophic carbon production, dissolved inorganic carbon fixation, respiration and the activity of the exoenzymes leucine aminopeptidase, alkaline phosphatase, beta-glucosidase and lipase. We found that both prokaryotic and eukaryotic communities were not significantly different inside the canyons (if compared to the close slope and overlying water), but they were rather shaped by the water masses dynamics in the area. The shallowest Modified Atlantic Waters, Levantine Intermediate Waters and Winter Intermediate Waters hosted higher percentages of Alphaproteobacteria, Bacteroidetes and Dinophyta, while the deepest Western Mediterranean Deep Waters hosted a higher fraction of Gammaproteobacteria, Chloroflexi, Discoba and Fungi. Among the functional measurements, only leucine aminopeptidase activity showed higher rates within the canyons. However, local hotspots within the canyons characterised by high particulate matter loads and high C:N ratio (interpreted as refractory material from sediment local resuspension) displayed pronounced degradation activities.

The influence of impactor size cut-off shift caused by hygroscopic growth on particulate matter loading and composition measurements

The mass loading and composition of atmospheric particles are important in determining their climate and health effects, and are typically measured by filter sampling. However, particle sampling under ambient conditions can lead to a shift in the size cut-off threshold induced by hygroscopic growth, and the influence of this on measurement of particle loading and composition has not been adequately quantified. Here, we propose a method to assess this influence based on κ-Köhler theory. A global perspective is presented based on previously reported annual climatological values of hygroscopic properties, meteorological parameters and particle volume size distributions. Measurements at background sites in Europe may be more greatly influenced by the cut-off shift than those from other continents, with a median influence of 10–20% on the total mass of sampled particles. However, the influence is generally much smaller (<7%) at urban sites, and is negligible for dust and particles in the Arctic. Sea-salt particles experience the largest influence (median value ∼50%), resulting from their large size, high hygroscopicity and the high relative humidity (RH) in marine air-masses. We estimate a difference of ∼30% in this influence of sea-salt particle sampling between relatively dry (RH = 60%) and humid (RH = 90%) conditions. Given the variation in the cut-off shift in different locations and at different times, a consistent consideration of this influence using the approach we introduce here is critical for observational studies of the long-term and spatial distribution of particle loading and composition, and crucial for robust validation of aerosol modules in modelling studies.

Seasonal variation in accumulation of mercury in the benthic macrofauna in a temperate coastal zone (Gulf of Gdańsk)

The main source of toxic mercury (Hg) in the human body is the consumption of fish and seafood. Therefore, it is particularly important to indicate the processes that condition Hg accumulation in marine organisms, especially those in the basal links of the food chain, which are rather poorly investigated compared to top predators. The aim of the study was to determine the seasonal variability of Hg concentrations in macrozoobenthic organisms and the factors that condition it. The research was conducted in 2012–2013 in a temperate coastal zone (Gulf of Gdańsk). The obtained results showed that both Hg concentrations within one trophic level, and their seasonal variation, may differ significantly if the organisms have different feeding habits. The research also indicated that the seasonal variability of Hg level in macrozoobenthos depended on a number of both biotic factors (primary production volume, biomass and rate of fauna metabolism) and abiotic factors (salinity and ionic composition of water, Eh). The variability of Hg concentrations in macrozoobenthos during the study period was different at the research stations, which were subjected to different land influence (e.g. surface run-off, coastal erosion), and consequently differed in the quantity and quality of organic matter. The increased load of suspended particulate matter (SPM) was also an important factor influencing the increase in Hg concentration in macrozoobenthos, regardless of their trophic status. This indicates that SPM is an important source of food for zoobenthos, even in species that prefer a different feeding strategies. The obtained results also showed the role of climate changes observed in the temperate zone - in particular, the warming of the winter season - in shaping the Hg level in macrozoobenthos. The accumulation of Hg in the bottom fauna occurred most intensively in spring immediately after a long period of icing - Hg concentrations were then much higher than those measured after a mild winter, during which the ice cover persisted for a short time. The warming of the winter season and the extension of the vegetation season contributed to an increase in macrozoobenthic biomass, and consequently to the biodilution of Hg, which could have had a negative effect on the Hg load introduced into the trophic chain.

Impact of particulate matter on basmati rice varieties grown in Indo-Gangetic Plains of India: Growth, biochemical, physiological and yield attributes

The study presents the first experimental evidence of the effects of atmospheric particulate matter (PM) deposition on two basmati (scented) rice varieties [Pusa Basmati-1509 (PB-1509) and Pusa Sugandh-5 (PS-5)] grown in Indo-Gangetic Plains (IGP) of India. Atmospheric PM load at the experimental site during rice crop growth period (August–November) was in the range of 162–660 μgm−3. The rice varieties growth, biochemical, physiological and yield attributes were monitored under three levels of PM deposition namely - low levels of PM deposition (LPM), ambient levels of PM deposition (APM) and elevated levels of PM deposition (EPM). PM deposition and PM flux on the canopy of rice varieties were 400–574 μgcm−2 and 24–58 μgcm−2day−1, respectively. PM deposition was 4.5% higher on the PS-5 than PB-1509 and among growth stages; it was the highest during the reproductive growth stage. Significant reduction in chlorophyll, leaf water and carotenoid content were observed in both varieties under EPM compared to APM. The air pollution tolerance index (APTI) also declined significantly. PM deposition enhanced leaf temperature (1–6%) of rice varieties under EPM compared to APM. The reduction in photosynthesis, stomatal conductance and transpiration of rice varieties under EPM were in the range of 9–52%; 6–40% and 8–46%, respectively compared to APM. PM deposition effects on plant height, the number of tillers and recoverable root biomass were found non-significant. PS-5 and PB-1509 exhibited 4–7% enhancement and 7.5–14% reduction in grain yield under LPM and EPM compared to APM, respectively. The results of the study indicate that increasing atmospheric PM pollution in IGP may adversely affect productivity and economic gains from scented basmati varieties of rice.

Forecasting the Impacts of Prescribed Fires for Dynamic Air Quality Management

Prescribed burning (PB) is practiced throughout the USA, most extensively in the southeast, for the purpose of maintaining and improving the ecosystem and reducing wildfire risk. However, PB emissions contribute significantly to trace gas and particulate matter loads in the atmosphere. In places where air quality is already stressed by other anthropogenic emissions, PB can lead to major health and environmental problems. We developed a PB impact forecasting system to facilitate the dynamic management of air quality by modulating PB activity. In our system, a new decision tree model predicts burn activity based on the weather forecast and historic burning patterns. Emission estimates for the forecast burn activity are input into an air quality model, and simulations are performed to forecast the air quality impacts of the burns on trace gas and particulate matter concentrations. An evaluation of the forecasts for two consecutive burn seasons (2015 and 2016) showed that the modeling system has promising forecasting skills that can be further improved with refinements in burn area and plume rise estimates. Since 2017, air quality and burn impact forecasts are being produced daily with the ultimate goal of incorporating them into the management of PB operations.

Is the Treatment Response of Manufactured BMPs to Urban Drainage PM Loads Portable?

AbstractHydrodynamic separators (HS) and basins/tanks such as rectangular clarifiers (RC), as unit operations (UOs) for particulate matter (PM) separation, are common smaller-footprint best managem...

The são Francisco river (NE): review on the interannual loading of particulate matter suspended to the ocean and impacts of dams

The order of magnitude of the global transport of materials through the rivers is still a controversial topic The S atilde o Francisco River NE Brazil Midsize L km AB x km is characterized by multiple uses and a system of dams in cascade This article is a review of the particulate matter suspended load in the San Francisco river through synthesizing grouping and comparing against other tropical rivers The annual flows of suspended particulate matter ranged from x t a to x t a for the hydrological years of and respectively Despite the existing dams system in the S atilde o Francisco there is considerable interannual variability in the suspended particulate material flow This variability is associated mainly with extreme hydrological events of floods when the inflows are higher than the storage capacity of dams generating large flows and large material loads The S atilde o Francisco River presents a lower yield of the suspended particulate matter when compared to other tropical rivers which can be attributed to its hydrographic basin presenting semi arid regions Besides the retention due to the cascade of dams contributes to the reduced yield

An Experimental Investigation into the Effect of NO2 and Temperature on the Passive Oxidation and Active Regeneration of Particulate Matter in a Diesel Particulate Filter

The kinetics of particulate matter (PM) oxidation in a catalyzed particulate filter (CPF) under different exhaust temperature and NO2 conditions is presented along with a literature review of the related PM kinetic studies. The study was conducted with a 2013 heavy-duty engine that had NO2 levels significantly higher than engines that met the earlier 2007/2010 EPA standards, and the results show a significant increase in PM oxidation rate that is possible under normal vehicle operating conditions, to diminish the need to actively regenerate the DPF. The detailed procedure for determining the PM oxidized during the experiments is described. Two types of tests were conducted to determine the NO2 assisted as well as the thermal oxidation kinetics. Passive Oxidation (PO) tests were conducted for selected engine conditions that would cover the range of exhaust NO2 concentrations (137 to 1013 ppm tested) and temperatures (299 to 388 °C tested) during regular engine operation. Active regeneration (AR) tests were conducted to determine the thermal oxidation kinetics at exhaust temperatures from 498 to 575 °C which was induced by post fueling. The CPF was first loaded with PM to a target loading, and then the PM was oxidized under specific exhaust temperature and NO2/O2 concentration conditions. The data obtained in this study can also be used to calibrate a CPF model. The activation energies and pre-exponential factors for NO2 assisted and thermal oxidation were developed from the PO and AR data. It was also found that PM reactivity during PM loading was greater than for the passive oxidation tests.

Evaluation of alternative filter media for particulate matter emission testing of residential wood heating devices

ABSTRACTThe performance of Teflon-coated glass fiber filter media (Pallflex Emfab TX40) is evaluated for particulate matter (PM) sampling of residential wood heating devices in a dilution tunnel. Thirty samples of varying duration and PM loading and concentration were collected from an U.S. Environmental Protection Agency (EPA) Method 28 dilution tunnel using dual Method 5G sample trains with untreated glass fiber and Emfab filters. Filters were weighed soon after the end of sampling and again the next day after equilibration at 35% relative humidity (RH). PM concentrations from both types of filters agreed very well with 1-day equilibration, demonstrating that Emfab filters are appropriate for use in measuring PM from residential wood burning appliances in a dilution tunnel and have performance equal to or better than the glass fiber filter media. Agreement between filter media without equilibration was erratic, with PM from glass fiber filter samples varying from slightly less than the Emfab samples to as much as 2.8 times higher. Some of the glass fiber filters lost substantial mass with equilibration, with the highest percent loss at lower filter mass loadings. Mass loss for Emfab samples was a small percentage of the mass and very consistent across the range of mass loadings. Taken together, these results may indicate water uptake on the glass fiber media that is readily removed with 1-day equilibration at moderate RH conditions.Implications: EPA regulations now allow the use of either glass fiber or Teflon filter media for wood appliance PM emission testing. Teflon filter media minimizes the potential for acid-gas PM artifacts on glass fiber filters; this is important as EPA moves toward the use of locally sourced cordwood for testing that may have higher sulfur content. This work demonstrates that the use of Teflon-coated glass fiber filters can give similar PM measurement results to glass fiber filters after 1 day of equilibration. With no equilibration, measured PM from glass fiber filters was usually higher than from Teflon-coated glass fiber filters.

Hydrological and biological processes modulate carbon, nitrogen and phosphorus flux from the St. Lawrence River to its estuary (Quebec, Canada)

Increased flux of carbon and nutrients from human activities in river basins were linked to acidification and deepwater hypoxia in estuaries and coastal areas worldwide. Annual loads (1995–2011) of suspended particulate matter (SPM), dissolved organic carbon (DOC), total nitrogen (TN) and total phosphorus (TP) were assessed at the Lake Ontario inlet of the St. Lawrence River (SLR) (7110 m3 s−1) and its estuarine outlet at Québec City (12,090 m3 s−1). Internal loads from the Ottawa River (1950 m3 s−1), seventeen other tributaries, urban wastewaters, atmospheric deposition and erosion were also estimated. Erosion (65% of SPM, 29% of TP), inflow from Lake Ontario (42% of DOC, 47% of TN) and Ottawa River (28% of DOC) contributed important flux to the estuary. Loads from other tributaries (20 and 27% of TN and TP at Quebec City) largely exceeded municipal sources (6% of exported TN and TP) and require future remediation. Aquatic plants fixed 277,000 t of C, 49,000 t of N and 7000 t of P (May–Sept.), delaying the nutrient flux to the estuary and turning the SLR into a nutrient sink over summers of lowest discharge. Degradation of exported organic C could consume 5.4–7.1 million t O2 year−1 in the estuary whereas SLR flux of N and P represent 31–47% and 7–14% of total annual estuarine flux, respectively. Carbon and Nitrogen flux from freshwaters partly explain the decline in pH and oxygen concentrations in deep estuarine waters thus highlighting the need to reduce diffuse sources of nutrients in the entire watershed.

Simultaneous measurements of particle number size distributions at ground level and 260 m on a meteorological tower in urban Beijing, China

Abstract. Despite extensive studies into the characterization of particle number size distributions at ground level, real-time measurements above the urban canopy in the megacity of Beijing have never been performed to date. Here we conducted the first simultaneous measurements of size-resolved particle number concentrations at ground level and 260 m in urban Beijing from 22 August to 30 September. Our results showed overall similar temporal variations in number size distributions between ground level and 260 m, yet periods with significant differences were also observed. Particularly, accumulation-mode particles were highly correlated (r2 = 0. 85) at the two heights, while Aitken-mode particles presented more differences. Detailed analysis suggests that the vertical differences in number concentrations strongly depended on particle size, and particles with a mobility diameter between 100 and 200 nm generally showed higher concentrations at higher altitudes. Particle growth rates and condensation sinks were also calculated, which were 3.2 and 3.6 nm h−1, and 2.8 × 10−2 and 2.9 × 10−2 s−1, at ground level and 260 m, respectively. By linking particle growth with aerosol composition, we found that organics appeared to play an important role in the early stage of the growth (09:00–12:00 LT) while sulfate was also important during the later period. Positive matrix factorization of size-resolved number concentrations identified three common sources at ground level and 260 m, including a factor associated with new particle formation and growth events (NPEs), and two secondary factors that represent photochemical processing and regional transport. Cooking emission was found to have a large contribution to small particles and showed much higher concentration at ground level than 260 m in the evening. These results imply that investigation of NPEs at ground level in megacities needs to consider the influences of local cooking emissions. The impacts of regional emission controls on particle number concentrations were also illustrated. Our results showed that regional emission controls have a dominant impact on accumulation-mode particles by decreasing gas precursors and particulate matter loadings, and hence suppressing particle growth. In contrast, the influences on Aitken particles were much smaller due to the enhanced new particle formation (NPF) events.