Evolution of planetary boundary layer under different weather conditions,and its impact on aerosol concentrations

A field experiment was conducted in Tianjin, China from September 9–30, 2010, focused on the evolution of Planetary Boundary Layer (PBL) and its impact on surface air pollutants. The experiment used three remote sensing instruments, wind profile radar (WPR), microwave radiometer (MWR) and micro-pulse lidar (MPL), to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants (aerosol, CO, SO₂, NO_x), and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000–1300 m during noon/afternoon-time, and 200–300 m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70 km while the averaged aerosol concentrations were 52 and 17 μg/m³ under haze and clear sky conditions, respectively. The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze (heavy pollution) or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle (more aerosols → lower PBL height → more aerosols) would induce an acceleration process for heavy ground pollution in megacities.     

Composition of carbohydrates,surfactants, major elements and anions in PM2.5 during the 2013 Southeast Asia high pollution episode in Malaysia

Haze episodes have become a major concern in Malaysia over the past few decades and have an increasingly important impact on the country each and every year. During haze episodes from biomass burning in Southeast Asia, particularly from Sumatra, Indonesia, particulate matter PM_2.5 is found to be one of the dangerous sources of airborne pollution and is known to seriously affect human health. This study determines the composition of carbohydrates (as levoglucosan), surfactants, major elements, and anions in PM_2.5 during a 2013 haze episode. PM_2.5 samples were collected from Universiti Kebangsaan Malaysia, Bangi, using a high volume sampler during a seven-day monitoring campaign during the peak of that year’s haze episode. PM_2.5 concentrations ranged between 14.52 and 160.93 μg/m³, exceeding the 2005 WHO air quality guidelines for PM_2.5 (25 μg/m³ for 24-h mean). The patterns for levoglucosan, surfactants, major elements, and anionic compositions were proportional to the PM_2.5 concentrations. Changes in PM_2.5 observed on days 3 and 4 were influenced by a combination of meteorological factors, which substantiate the theory that such factors play a pivotal role in haze episodes.     

Observation and analysis of near-surface atmospheric aerosol optical properties in urban Beijing

Year-round measurements of the mass concentration and optical properties of fine aerosols (PM_2.5) from June 2009 to May 2010 at an urban site in Beijing were analyzed. The annual mean values of the PM_2.5 mass concentration, absorption coefficient (Ab), scattering coefficient (Sc) and single scattering albedo (SSA) at 525 nm were 67 ± 66 μg/m³, 64 ± 62 Mm⁻¹, 360 ± 405 Mm⁻¹ and 0.82 ± 0.09, respectively. The bulk mass absorption efficiency and scattering efficiency of the PM_2.5 at 525 nm were 0.78 m²/g and 5.55 m²/g, respectively. The Ab and Sc showed a similar diurnal variation with a maximum at night and a minimum in the afternoon, whereas SSA displayed an opposite diurnal pattern. Significant increases in the Ab and Sc were observed in pollution episodes caused by the accumulation of pollutants from both local and regional sources under unfavorable weather conditions. Aerosol loadings in dust events increased by several times in the spring, which had limited effects on the Ab and Sc due to the low absorption and scattering efficiency of dust particles. The frequency of haze days was the highest in autumn because of the high aerosol absorption and scattering under unfavorable weather conditions. The daily PM_2.5 concentration should be controlled to a level lower than 64 μg/m³ to prevent the occurrence of haze days according to its exponentially decreased relationship with visibility.     

Real-time measurements of PM2.5, PM10–2.5, and BC in an urban street canyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM_2.5, PM_10–2.5, and Black Carbon (BC) over a 12-month period in an urban street canyon of Hong Kong. Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded. The average weekly cycles of PM_2.5, PM_10–2.5, and BC suggested that all species are related to traffic, with high concentrations on workdays and low concentrations over the weekends. PM_2.5 exhibited two comparable concentrations at 10:00–11:00 (63.4 μg/m³) and 17:00–18:00 (65.0 μg/m³) local time (LT) during workdays, corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels: 3179 and 2907 h⁻¹, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2 μg/m³) during the midday period (10:00–11:00 LT) on workdays. A poor correlation was found between PM_2.5 concentration and wind speed (R = 0.51, P-value > 0.001). In contrast, the concentration of PM_10–2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R = 0.98, P-value < 0.0001).     

Chemical characteristics of PM2.5 during haze episodes in the urban of Fuzhou,China

Atmospheric fine particles (PM_2.5) were collected in this study with middle volume samplers in Fuzhou, China, during both normal days and haze days in summer (September 2007) and winter (January 2008). The concentrations, distributions, and sources of polycyclic aromatic hydrocarbons (PAHs), organic carbon (OC), elemental carbon (EC), and water soluble inorganic ions (WSIIs) were determinated. The results showed that the concentrations of PM_2.5, PAHs, OC, EC, and WSIIs were in the orders of haze > normal and winter > summer. The dominant PAHs of PM_2.5 in Fuzhou were Fluo, Pyr, Chr, BbF, BkF, BaP, BghiP, and IcdP, which represented about 80.0% of the total PAHs during different sampling periods. The BaPeq concentrations of ∑PAHs were 0.78, 0.99, 1.22, and 2.43 ng/m³ in summer normal, summer haze, winter normal, and winter haze, respectively. Secondary pollutants (SO₄^2?, NO₃^?, NH₄⁺, and OC) were the major chemical compositions of PM_2.5, accounting for 69.0%, 55.1%, 63.4%, and 64.9% of PM_2.5 mass in summer normal, summer haze, winter normal, and winter haze, respectively. Correspondingly, secondary organic carbon (SOC) in Fuzhou accounted for 20.1%, 48.6%, 24.5%, and 50.5% of OC. The average values of nitrogen oxidation ratio (NOR) and sulfur oxidation ratio (SOR) were higher in haze days (0.08 and 0.27) than in normal days (0.05 and 0.22). Higher OC/EC ratios were also found in haze days (5.0) than in normal days (3.3). Correlation analysis demonstrated that visibility had positive correlations with wind speed, and negative correlations with relative humidity and major air pollutants. Overall, the enrichments of PM_2.5, OC, EC, SO₄^2?, and NO₃^? promoted haze formation. Furthermore, the diagnostic ratios of IcdP/(IcdP + BghiP), IcdP/BghiP, OC/EC, and NO₃^?/SO₄^2? indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Fuzhou.     

PM2.5 in an industrial district of Zhengzhou,China: Chemical composition and source apportionment

Zhengzhou is a developing city in China, that is heavily polluted by high levels of particulate matter. In this study, fine particulate matter (PM_2.5) was collected and analyzed for their chemical composition (soluble ions, elements, elemental carbon (EC) and organic carbon (OC)) in an industrial district of Zhengzhou in 2010. The average concentrations of PM_2.5 were 181, 122, 186 and 211 μg/m³ for spring, summer, autumn and winter, respectively, with an annual average of 175 μg/m³, far exceeding the PM_2.5 regulation of USA National Air Quality Standards (15 μg/m³). The dominant components of PM_2.5 in Zhengzhou were secondary ions (sulphate and nitrate) and carbon fractions. Soluble ions, total carbon and elements contributed 41%, 13% and 3% of PM_2.5 mass, respectively. Soil dust, secondary aerosol and coal combustion, each contributing about 26%, 24% and 23% of total PM_2.5 mass, were the major sources of PM_2.5, according to the result of positive matrix factorization analysis. A mixed source of biomass burning, oil combustion and incineration contributed 13% of PM_2.5. Fine particulate matter arising from vehicles and industry contributed about 10% and 4% of PM_2.5, respectively.     

Characteristics of black carbon aerosol in Jiaxing,China during autumn 2013

We conducted measurements of black carbon (BC) aerosol in Jiaxing, China during autumn from September 26 to November 30, 2013. We investigated temporal and diurnal variations of BC, and its correlations with meteorological parameters and other major pollutants. Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m³, with an average of 5.1 μg/m³. The diurnal variation of BC exhibited a bimodal distribution, with peaks at 07:00 and 18:00. The morning peak was larger than the evening peak. The mass percentages of BC in PM_2.5 and PM₁₀ were 7.1% and 4.8%, respectively. The absorption coefficient of BC was calculated to be 44.4 Mm⁻¹, which accounted for 11.1% of the total aerosol extinction. BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m³ during the measurement period. Correlation analysis indicated that the main sources of BC were motor vehicle exhaust, and domestic and industrial combustion.     

Impact of meteorological conditions on a nine-day particulate matter pollution event observed in December 2013, Shanghai,China

A severe particulate matter pollution event occurred in Shanghai from 1 to 9 December 2013. The mean hourly mass concentrations of PM_2.5 and PM₁₀ were 211.9 and 249.0 μg/m³, respectively. Reanalysis data, in situ, and remote-sensing measurements were used to examine the impacts of meteorological conditions on this event. It was found that the synoptic pattern of weak pressure, the reduced planetary boundary layer height, and the passage of two cold fronts were key factors causing the event. Four stages were identified during this event based on the evolution of its PM_2.5 levels and weather conditions. The highest concentration of PM_2.5 (602 μg/m³) was observed in stage 3. High PM_2.5 concentrations were closely associated with a low local ventilation index, with an average of 505 m²/s, as well as with the influx of pollutants from upstream, transported by the cold fronts.     

Light attenuation cross-section of black carbon in an urban atmosphere in northern China

Fine particulate matter (PM_2.5) samples were collected over two years in Xi’an, China to investigate the relationships between the aerosol composition and the light absorption efficiency of black carbon (BC). Real-time light attenuation of BC at 880 nm was measured with an aethalometer. The mass concentrations and elemental carbon (EC) contents of PM_2.5 were obtained, and light attenuation cross-sections (σ_ATN) of PM_2.5 BC were derived. The mass of EC contributed ∼5% to PM_2.5 on average. BC σ_ATN exhibited pronounced seasonal variability with values averaging 18.6, 24.2, 16.4, and 26.0 m²/g for the spring, summer, autumn, and winter, respectively, while averaging 23.0 m²/g overall. σ_ATN varied inversely with the ratios of EC/PM_2.5, EC/[SO₄²⁻], and EC/[NO₃⁻]. This study of the variability in σ_ATN illustrates the complexity of the interactions among the aerosol constituents in northern China and documents certain effects of the high EC, dust, sulfate and nitrate loadings on light attenuation.     

Particulate pollution in an underground car park in Wuhan,China

Particulate matter (PM) pollution in an underground car park in Wuhan was investigated. Mass concentrations of PM₁₀ and PM_2.5 were obtained using gravimetric method. Selected metal elements, such as Fe, Mn, Zn, Pb, and Cu in PM₁₀ samples, were determined using atomic absorption spectrometer (AAS). Beta attenuation method was applied to observe the hourly variation of PM₁₀ levels. Results show that average PM₁₀ concentrations at the entrance and at the exit were 101.3 μg/m³ and 234.4 μg/m³, respectively, and average PM_2.5 concentrations at the entrance and at the exit were 47.7 μg/m³ and 62.7 μg/m³, respectively. PM pollution was worse at the exit than at the entrance. Hourly PM₁₀ concentration was weakly correlated with traffic flow. Regarding element concentrations, the most enriched element in PM₁₀ samples was Fe. Re-suspension of soil dust at the exit is an important source of PM₁₀.     

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu,China

Daily fine particulate (PM_2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms (DSs) and several types of pollution events, including haze (HDs), biomass burning (BBs), and fireworks displays (FDs). The highest PM_2.5 mass concentrations were found during DSs (283.3 μg/m³), followed by FDs (212.7 μg/m³), HDs (187.3 μg/m³), and BBs (130.1 μg/m³). The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions (NO₃^?, SO₄^2?, and NH₄⁺) were enriched during HDs, while PM_2.5 from BBs showed high K⁺ but low SO₄^2?. FDs caused increases in K⁺ and enrichment in SO₄^2?. Ca²⁺ was abundant in DS samples. Ion-balance calculations indicated that PM_2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon (OC) concentration was 26.1 μg/m³ during FDs, followed by BBs (23.6 μg/m³), HDs (19.6 μg/m³), and DSs (18.8 μg/m³). In contrast, elemental carbon (EC) concentration was more abundant during HDs (10.6 μg/m³) and FDs (9.5 μg/m³) than during BBs (6.2 μg/m³) and DSs (6.0 μg/m³). The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO₄^2?/K⁺ and TCA/SO₄^2? ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO₄^2?, and NO₃^? were the dominant chemical components during pollution events, while soil dust was dominant during DSs.     

Spatiotemporal variations of PM2.5 and PM10 concentrations between 31 Chinese cities and their relationships with SO2, NO2, CO and O3

The variations of mass concentrations of PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃ in 31 Chinese provincial capital cities were analyzed based on data from 286 monitoring sites obtained between March 22, 2013 and March 31, 2014. By comparing the pollutant concentrations over this length of time, the characteristics of the monthly variations of mass concentrations of air pollutants were determined. We used the Pearson correlation coefficient to establish the relationship between PM_2.5, PM₁₀, and the gas pollutants. The results revealed significant differences in the concentration levels of air pollutants and in the variations between the different cities. The Pearson correlation coefficients between PMs and NO₂ and SO₂ were either high or moderate (PM_2.5 with NO₂: r = 0.256–0.688, mean r = 0.498; PM₁₀ with NO₂: r = 0.169–0.713, mean r = 0.493; PM_2.5 with SO₂: r = 0.232–0.693, mean r = 0.449; PM₁₀ with SO₂: r = 0.131–0.669, mean r = 0.403). The correlation between PMs and CO was diverse (PM_2.5: r = 0.156–0.721, mean r = 0.437; PM₁₀: r = 0.06–0.67, mean r = 0.380). The correlation between PMs and O₃ was either weak or uncorrelated (PM_2.5: r = −0.35 to 0.089, mean r = −0.164; PM₁₀: r = −0.279 to 0.078, mean r = −0.127), except in Haikou (PM_2.5: r = 0.500; PM₁₀: r = 0.509).     

Source apportionment of PM10 in Delhi,India using PCA/APCS,UNMIX and PMF

Source apportionment of particulate matter (PM₁₀) measurements taken in Delhi, India between January 2013 and June 2014 was carried out using two receptor models, principal component analysis with absolute principal component scores (PCA/APCS) and UNMIX. The results were compared with previous estimates generated using the positive matrix factorization (PMF) receptor model to investigate each model’s source-apportioning capability. All models used the PM₁₀ chemical composition (organic carbon (OC), elemental carbon (EC), water soluble inorganic ions (WSIC), and trace elements) for source apportionment. The average PM₁₀ concentration during the study period was 249.7 ± 103.9 μg/m³ (range: 61.4–584.8 μg/m³). The UNMIX model resolved five sources (soil dust (SD), vehicular emissions (VE), secondary aerosols (SA), a mixed source of biomass burning (BB) and sea salt (SS), and industrial emissions (IE)). The PCA/APCS model also resolved five sources, two of which also included mixed sources (SD, VE, SD+SS, (SA+BB+SS) and IE). The PMF analysis differentiated seven individual sources (SD, VE, SA, BB, SS, IE, and fossil fuel combustion (FFC)). All models identified the main sources contributing to PM₁₀ emissions and reconfirmed that VE, SA, BB, and SD were the dominant contributors in Delhi.     

PM2.5 in China: Measurements,sources, visibility and health effects,and mitigation

Concern over the health effects of fine particles in the ambient environment led the U.S. Environmental Protection Agency to develop the first standard for PM_2.5 (particulate matter less than 2.5 μm) in 1997. The Particle Technology Laboratory at the University of Minnesota has helped to establish the PM_2.5 standard by developing many instruments and samplers to perform atmospheric measurements. In this paper, we review various aspects of PM_2.5, including its measurement, source apportionment, visibility and health effects, and mitigation. We focus on PM_2.5 studies in China and where appropriate, compare them with those obtained in the U.S. Based on accurate PM_2.5 sampling, chemical analysis, and source apportionment models, the major PM_2.5 sources in China have been identified to be coal combustion, motor vehicle emissions, and industrial sources. Atmospheric visibility has been found to correlate well with PM_2.5 concentration. Sulfate, ammonium, and nitrate carried by PM_2.5, commonly found in coal burning and vehicle emissions, are the dominant contributors to regional haze in China. Short-term exposure to PM_2.5 is strongly associated with the increased risk of morbidity and mortality from cardiovascular and respiratory diseases in China. The strategy for PM_2.5 mitigation must be based on reducing the pollutants from the two primary sources of coal-fired power plants and vehicle emissions. Although conventional Particulate Emission Control Devices (PECD) such as electrostatic precipitators in Chinese coal-fired power plants are generally effective for large particles, most of them may not have high collection efficiency of PM_2.5. Baghouse filtration is gradually incorporated into the PECD to increase the PM_2.5 collection efficiency. By adopting stringent vehicle emissions standard such as Euro 5 and 6, the emissions from vehicles can be gradually reduced over the years. An integrative approach, from collaboration among academia, government, and industries, can effectively manage and mitigate the PM_2.5 pollution in China.     

Local and long-range transport influences on PM2.5 at a cities-cluster in northern China,during summer 2008

Hourly PM_2.5 concentrations were observed simultaneously at a cities-cluster comprising 10 cities/towns in Hebei province in China from July 1 to 31, 2008. Among the 10 cities/towns, Baoding showed the highest average concentration level (161.57 μg/m³) and Yanjiao exhibited the lowest (99.35 μg/m³). These observed data were also studied using the joint potential source contribution function with 24-h and 72-h backward trajectories, to identify more clearly the local and countrywide-scale long-range transport sources. For the local sources, three important influential areas were found, whereas five important influential areas were defined for long-range transport sources. Spatial characteristics of PM_2.5 were determined by multivariate statistical analyses. Soil dust, coal combustion, and vehicle emissions might be the potential contributors in these areas. The results of a hierarchical cluster analysis for back trajectory endpoints and PM_2.5 concentrations datasets show that the spatial characteristics of PM_2.5 in the cities-cluster were influenced not only by local sources, but also by long-range transport sources. Different cities in the cities-cluster obtained different weighted contributions from local or long-range transport sources. Cangzhou, Shijiazhuang, and Baoding are near the source areas in the south of Hebei province, whereas Zhuozhou, Yangfang, Yanjiao, Xianghe, and Langfang are close to the sources areas near Beijing and Tianjin.     

Variation of PM2.5 concentration in Hangzhou,China

This observational study investigates the variation of PM_2.5 concentration and its ratio against PM₁₀ concentration under different weather systems and pollution types. The study was conducted in Hangzhou on east China's Yangtze River Delta using data collected at seven ambient air quality monitoring stations around the metropolitan area between 2006 and 2008 and using weather information in the same period. Nine predominant weather systems affecting the city were classified through careful analysis of the 11-year surface and upper air weather charts from 1996 to 2006. Each observational day was then assigned to one of the nine weather systems. It was found that the PM_2.5 concentration varied greatly for different weather systems, with the highest PM_2.5 concentration associated with the post-cold-frontal system at 0.091 mg/m³ and the lowest PM_2.5 concentration with the easterlies system at 0.038 mg/m³, although the PM_2.5/PM₁₀ ratio remained consistently above 0.5 for all systems. The post-cold-frontal system typically occurs in autumn and winter while the easterlies system is more a summer phenomenon. Among all types of pollution, the highest PM_2.5 concentration of 0.117 mg/m³ coincided with the large-scale continuous pollution events, suggesting that this type of pollution was more conducive to the formation of secondary particulate matters. The ratio of PM_2.5/PM₁₀ was above 0.5 in non-pollution days and all pollution types but one under the influence of dust storms when the ratio decreased to 0.3 or less. The outcomes of this study could be used to develop a rudimental predictive model of PM_2.5 concentration based on weather system and pollution type.     

Transport of black carbon aerosols from non-local sources: A case study in Shanghai

Black carbon (BC) aerosol mass carried by winds of varying directions from non-local sources was estimated based on hourly measured data of BC mass concentration (C_BC) and meteorological parameters from January 2008 to December 2012 in Shanghai, and the relationship between annual average C_BC and wind speed was analyzed. The results show that the annual average C_BC decreased with wind speed for speeds exceeding 0.3 m/s. The relationship between the two was determined by a linear fit with correlation coefficient 0.88. Assuming BC aerosol mass of non-local sources transported by a southeast wind was zero, annual average BC concentrations (μg/m³) carried by winds of variable direction were 1.99 (southwest), 1.95 (west), 1.15 (northwest), 0.54 (south), 0.39 (north), 0.01 (northeast), and 0.01 (east). BC aerosol mass of non-local sources transported by wind to Shanghai was about 6404.05 t per year, among which the total contribution of southwest, west, and northwest winds was nearly 84%. The aerosol mass transported to Shanghai in winter accounted for 35% that of the entire year, and was greater than that of the other seasons.     

Multiyear analyses of ground-level air contaminants over Paris metropolitan region using real-time observations and air mass backward trajectories

For the years 2008–2013, particles of diameter <10 and 2.5 μm (PM₁₀ and PM_2.5, respectively), NO_x, SO₂, and O₃ concentrations at urban, suburban, rural, and traffic sites in the Paris metropolitan area were analyzed. Strong spatial variability at traffic and rural sites and relatively uniform profiles at urban and suburban sites for PM₁₀, PM_2.5, and O₃ were observed. The O₃ weekend effect was induced by lower NO_x emissions during the weekend, and favored volatile organic compounds (VOCs)-limited atmospheric conditions. In conjunction with low ambient temperature, these conditions could also favor increased formation of secondary particulate nitrates in winter. Winter air pollution events were associated with multiple pollutants, whereas those observed in spring were caused by high PM₁₀ and PM_2.5 levels. Backward trajectory analyses showed the contribution of sources in Western and Central Europe on days with high PM₁₀, PM_2.5, and O₃, and a local/national component for NO_x and SO₂.     

Modeling nitrate aerosol distributions and its direct radiative forcing in East Asia with RAMS-CMAQ

The geographical and seasonal characteristics in nitrate aerosol and its direct radiative forcing over East Asia are analyzed by using the air quality modeling system RAMS-CMAQ coupled with an aerosol optical properties/radiative transfer module. For evaluating the model performance, nitrate ion concentration in precipitation, and mixing ratios of PM₁₀, and some gas precursors of aerosol during the whole year of 2007 are compared against surface observations at 17 stations located in Japan, Korea, and China, and the satellite retrieved NO₂ columns. The comparison shows that the simulated values are generally in good agreement with the observed ones. Simulated monthly averaged values are mostly within a factor of 2 of the measurements at the observation stations. The distribution patterns of NO₂ from simulation and satellite measurement are also similar with each other. Analysis of the distribution features of monthly and yearly averaged mass concentration and direct radiative forcing (DRF) of nitrate indicates that the nitrate aerosol could reach about 25–30% of the total aerosol mass concentration and DRF in Sichuan Basin, Southeast China, and East China where the high mass burden of all major aerosols concentrated. The highest mass concentration and strongest DRF of nitrate could exceed 40 μg/m³ and ?5 W/m², respectively. It also indicates that other aerosol species, such as carbonaceous and mineral particles, could obviously influence the nitrate DRF for they are often internally mixed with each other.     

The contribution of small leaks in a baghouse filter to dust emission in the PM2.5 range—A system approach

The contribution of leakage in a baghouse filter (defined as a short circuit between the upstream and downstream sides of the filter) to the emission of fine particles is quantified in comparison to other dust emission sources, and the influence of key operating variables on overall system response is analyzed. The study was conducted on a well-maintained pilot-scale filter unit (9 bags of 500 g/m² calendered polyester needle felt; total surface area 4.2 m²) operated in Δp-controlled mode over a range of pulsing intensities, with two types of test dust (one free-flowing and the other cohesive) at inlet concentrations of 10 and 30 g/m³. Leaks included single holes between 0.5 and 4 mm diameter, intentionally placed in either the plenum plate or one of the filter bags, as well as seamlines from bag confectioning. Emissions were separated by source into a transient contribution due to dust penetration through the filter bags after each cleaning pulse, and a continuous contribution from leaks. This separation was based on a novel method of data processing that relies on time-resolved concentration measurements with a specially calibrated optical particle counter. Tiny leaks on the order of 1 mm generated the same emission level as all the bags combined, and dominated continuous emissions. The equivalent leak cross section (leakage = media emission) was about 1 ppm of the total installed filter surface, independent of upstream dust concentration. Leakage through open seamlines amounted to 75% of media emissions in case of free-flowing test dust. Leakage was restricted to aerodynamic diameters less than ∼5 μm (roughly the PM_2.5 mass fraction). For comparison, time-averaged mass penetration through conventional needle-felt media ranged from about 10⁻⁵ to 10⁻⁶, depending on cohesiveness of the particle material and pulse cleaning intensity, giving emission levels between about 0.02 and 0.2 mg/m³ at the reference concentration of 10 g/m².