Hong Kong vehicle emission changes from 2003 to 2015 in the Shing Mun Tunnel
Xiaoliang Wanga, Kin-Fai Hob, Judith C. Chowa, Steven D. Kohla, Chi Sing Chanb, Long Cuic, Shun-cheng Frank Leec, Lung-Wen Antony Chend, Steven Sai Hang Hoe,f, Yan Chengg, and John G. Watsona
aDesert Research Institute, Reno, Nevada, USA; bThe Chinese University of Hong Kong, Hong Kong, China; cCivil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, China; dEnvironmental and Occupational Health, University of Nevada–Las Vegas, Las Vegas, Nevada, USA; eHong Kong Premium Services and Research Laboratory, Hong Kong, China; fInstitute of Earth Environment, Chinese Academy of Sciences, Xi’an, Shaanxi, China; gSchool of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, China
A B S T R A C T
This study characterized motor vehicle emission rates and compositions in Hong Kong’s Shing Mun tunnel (SMT) during 2015 and compared them to similar measurements from the same tunnel in 2003. Average PM2.5 concentrations in the SMT decreased by »70% from 229.1 § 22.1 mg/m3 in 2003 to 74.2 § 2.1 mg/m3 in 2015. Both PM2.5 and sulfur dioxide (SO2) emission factors (EFD) were reduced by »80% and total non-methane (NMHC) hydrocarbons EFD were reduced by 44%. These reductions are consistent with long-term trends of roadside ambient concentrations and emission inventory estimates, indicating the effectiveness of emission control measures. EFD changes between 2003 and 2015 were not statistically significant for carbon monoxide (CO), ammonia (NH3), and nitrogen oxides (NOx). Tunnel nitrogen dioxide (NO2) concentrations and NO2/NOx volume ratios increased, indicating an increased NO2 fraction in the primary vehicle exhaust emissions. Elemental carbon (EC) and organic matter (OM) were the most abundant PM2.5 constituents, with EC and OM, respectively, contributing to 51 and 31% of PM2.5 in 2003, and 35 and 28% of PM2.5 in 2015. Average EC and OM EFD decreased by »80% from 2003 to 2015. The sulfate EFD decreased to a lesser degree (55%) and its contribution to PM2.5 increased from 10% in 2003 to 18% in 2015, due to influences from ambient background sulfate concentrations. The contribution of geological materials to PM2.5 increased from 2% in 2003 to 5% in 2015, signifying the importance of nontailpipe emissions.
Investigating particle emissions and aerosol dynamics from a consumer fused
deposition modeling 3D printer with a lognormal moment aerosol model
Qian Zhanga, Girish Sharmab, Jenny P. S. Wongc, Aika Y. Davisd, Marilyn S. Blackd, Pratim Biswasb,
and Rodney J. Weberc
aSchool of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA; bDepartment of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA; cSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georia, USA; dChemical Safety, Underwriters Laboratories Inc., Marietta, Georgia, USA
A B S T R A C T
Particle emissions from consumer-fused deposition modeling 3D printers have been reported previously; however, the complex processes leading to observed aerosols have not been investigated. We measured particle concentrations and size distributions between 7 nm and 25 mm emitted from a 3D printer under different conditions in an emission test chamber. The experimental
data was combined with a moment lognormal aerosol dynamic model to better understand particle formation and subsequent evolution mechanisms. The model was based on particles being formed from nucleation of unknown semivolatile compounds emitted from the heated filament during printing, which evolve due to condensation of emitted vapors and coagulation, all within a small volume near the printer extruder nozzle. The model captured observed steady state particle number size distribution parameters (total number, geometric mean diameter and geometric standard deviation) with errors nominally within 20%. Model solutions provided a range of vapor generation rates, saturation vapor pressures and vapor condensation factors consistent with
measured steady state particle concentrations and size distributions. Vapor generation rate was a crucial factor that was linked to printer extruder temperature and largely accounted for differences between filament material and brands. For the unknown condensing vapor species, saturation vapor pressures were in the range of 10¡3 to 10¡1 Pa. The model suggests particles could be
removed by design of collection surfaces near the extruder tip.
A diethylene glycol condensation particle counter for rapid sizing of
sub-3 nm atmospheric clusters
Chongai Kuang
Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, New York, USA
ABSTRACT
This article describes the modification of a laminar flow, thermally diffusive universal-fluid condensation particle counter (standard operation: 50% detection efficiency at 5 nm) to rapidly measure the size distribution of sub 3 nm aerosol. Sub 3 nm detection was achieved by using diethylene glycol as the working fluid, which enabled high instrument super-saturations while minimizing homogenous nucleation of the working fluid; a detection efficiency of 50% was achieved at 1.6 nm with laboratory-generated ammonium sulfate (AS) aerosol. Rapid aerosol sizing beneath 3 nm was achieved by inverting the measured grown droplet size distribution (1 s sampling) to recover the sampled aerosol size distribution. The developed inversion algorithm utilizes analytical kernel functions determined from the instrument response to pseudo-monodisperse AS aerosol from 1.5 nm to 20 nm, generated by a high-resolution DMA and a nano DMA. The inversion algorithm was tested numerically with assumed, idealized aerosol size distributions consistent with observed new particle formation events, yielding a reasonable agreement between inverted and assumed aerosol size distributions below 3 nm. This technique provides a measure of the aerosol size assuming an aerosol composition identical to that of the aerosol used to generate the experimentally determined kernel function.
Physicochemical properties and oxidative potential of fine particles
produced from coal combustion
Hung Soo Jooa,b, Tsatsa Batmunkha, Lucille Joanna S. Borlazaa, Minhan Parka, Kwang Yul Leea, Ji Yi Leec, Yu Woon Changc, and Kihong Parka
aNational Leading Research Laboratory (Aerosol Technology and Monitoring Laboratory), School of Environmental Science and
Engineering, Gwangju Institute of Science and Technology (GIST), Buk-gu, Gwangju, Republic of Korea; bDepartment of Environmental Engineering, Anyang University, Anyang, Manan-gu, Anyang-si, Gyeonggi-do, Republic of Korea; cDepartment of Environmental Engineering, Chosun University, Dong-gu, Gwangju, Republic of Korea
ABSTRACT
The physical and chemical properties as well as the oxidative potential (OP) of water soluble components of coal combustion fine particles were examined. A laboratory-scale pulverized-coal burning system was used to produce coal combustion particles at different burning temperatures of 550 C, 700 C, 900 C, and 1,100 C. Few studies have reported the effects of burning temperature on both the chemistry and toxicity of coal combustion particles. The highest mass emission factor of particulate matter less than 2.5 mm (PM2.5) was found to be produced at 700 C (3.51 g/kg), owing to strong elemental carbon (EC) emission and ash formation (ions and elements) resulting from the incomplete combustion of tar and char, and mineral fragmentation. The highest organic carbon in PM2.5 was found at 550 C. At a temperature higher than 700 C, the fraction of carbonaceous species decreased
while the fractions of ions and elements increased owing to ash formation. Sulfate was found to be the dominant ionic species, followed by sodium, calcium, and magnesium. The highest emission of elements (Al, As, Ba, Cd, Co, Cu, Fe, Mn, Ni, Pb, Sr, Ti, V, and Zn) and the highest fractions of Fe and Al were observed at 700 C. Intrinsic OP activities obtained from dithiothreitol (DTT) and electron spin resonance (ESR) assays showed the highest values at 550 C, suggesting that fine particles from lowtemperature coal combustion had the highest reactive oxygen species generation capability (potentially toxic) among various tested burning temperatures. The results of principal component analysis suggested a correlation between OP-DTT activity and OC, EC, Cd, Co, V, and Zn, while OP-ESR activity was associated with chloride, nitrate, Ba, Pb, Sr, and Ti.
Retrieving the ion mobility ratio and aerosol charge fractions for a
neutralizer in real-world applications
Xiaotong Chena and Jingkun Jianga,b
aState Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China; bState Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing, China
ABSTRACT
Electrical mobility size spectrometers (with a neutralizer, an electrical mobility classifier, and a detector as key components) are widely used to measure aerosol size distributions. The performance of a neutralizer is often evaluated separately from the spectrometer. In realworld applications of a neutralizer, i.e., typically with uncontrolled composition of the neutralizer carrier gas including trace constituents that can lead to variabilities in properties of positive and negative ions, charge fractions may differ from those predicted by widely used aerosol charging models with fixed ion properties and subsequently cause significant uncertainties in reported aerosol size distributions. In this study, we proposed an empirical method to retrieve the variations in neutralizer ion properties and aerosol charge fractions when measuring aerosol size distributions. Our approach requires measuring both positively and negatively charged particles using the electrical mobility size spectrometer to provide
information on the performance of the neutralizer. Bipolar diffusion charging theories were applied to illustrate that aerosol charge fractions are governed by the mobility ratio of positive and negative ions. Positively and negatively charged particles measured by the spectrometer can be used to estimate the mobility ratio of positive and negative ions for the neutralizer. A modified Gunn and Woessner’s formula can then be used to calculate aerosol charge fractions from the retrieved ion mobility ratio. These charge fractions can be used for size distribution data inversion. Both simulated aerosols and experiments were used to evaluate the proposed method. We found that this new method can capture the variations in neutralizer ion properties and aerosol charge fractions under various conditions and help to achieve more accurate measurement of aerosol size distributions.
Counting efficiency evaluation of optical particle counters in micrometer
range by using an inkjet aerosol generator
Kenjiro Iida and Hiromu Sakurai
Particle Measurement Research Group, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
ABSTRACT
This study introduces the method to evaluate the counting efficiencies of optical particle counters (OPCs), g, at particle diameter greater than 1 lm by using an inkjet aerosol generator (IAG). This study demonstrates the evaluations at 5 and 10 lm in volume equivalent diameter. The chemical composition of the particles is either sodium chloride or lactose monohydrate. The aerosol flowrate of the IAG is set at 0.3 L/min, and the aerosol is delivered to an OPC with sampling flowrate 6 L/min (Omron, ZN-PD50S). The mismatch of the flowrates is compensated for by adding particle-free air in a laminar flow chamber. In order to simulate the sampling of uniformly mixed aerosol from a real environment, the particles are delivered to different points over the inlet plane of the isokinetic probe attached to the OPC. Particle flux into the isokinetic probe is proportional to the gas-velocity
into the probe; however, the true velocity distribution is usually unknown. It is assumed that the true velocity distribution is bounded by two flow models: the plug and parabolic flows. A set of delivery points are prepared to simulate the particle flux under each flow model. Experimental results show that the choice of flow model influences the value of g at 10 lm indicating g is potentially different from the true value since the true value can be evaluated only if the true velocity distribution is known. The potential bias in g is considered as a source of systematic error in our uncertainty analysis.
Water condensation-based nanoparticle charging system: Physical and
chemical characterization
Nathan M. Kreisberga, Steven R. Spielmana, Arantzazu Eiguren-Fernandeza, Susanne V. Heringa,
Michael J. Lawlerb, Danielle C. Draperb, and James N. Smithb
aAerosol Dynamics Inc., Berkeley, California, USA; bDepartment of Chemistry, University of California, Irvine, Irvine, California, USA
ABSTRACT
A water condensation-based ion charging system has been developed to enhance both the charging efficiency and the concentration of sub-20 nm particles. This NanoCharger consists of a bipolar ion source followed by a parallel plate water-based condensation system, an embedded ion scavenger, and an aerodynamic focusing stage. Sufficient numbers of ions are transported through the system to attach to the formed droplets. An ion scavenger removes the ions immediately after the droplet formation to minimize multiple charging. A subsequent cold-walled condensation stage removes most of the water vapor, lowering the dew point to below 16 C, while a set of focusing nozzles concentrates the droplets into 10% of the flow. The flow is then slightly heated to evaporate the droplets. The physical enhancement of electrical charging was evaluated in the laboratory using mobility-selected particles, and found to provide 40-fold enhancement over bipolar charging for 6–15 nm particles. Chemical artifacts were evaluated through thermal desorption chemical ionization mass spectrometry. Data comparing ion spectra for flow that passed through the NanoCharger to that obtained without it showed nearly equivalent ion spectra, indicating that no significant artifacts were introduced from the condensation–evaporation process.
Chemistry of hydroperoxycarbonyls in secondary organic aerosol
Demetrios Pagonisa,b and Paul J. Ziemanna,b
aDepartment of Chemistry, University of Colorado, Boulder, Colorado, USA; bCooperative Institute for Research in Environmental Sciences (CIRES), Boulder, Colorado, USA
ABSTRACT
Highly oxidized multifunctional compounds (HOMs) formed through gas-phase reactions are thought to account for a significant fraction of the secondary organic aerosol (SOA) formed in low-nitric oxide (NO) environments. HOMs are known to be peroxide-rich and unstable in SOA, however, and their fate once they partition into particles is not well understood. In the study reported here, we identified particle-phase reactions and decomposition products for an a-alkoxy hydroperoxyaldehyde that served as a convenient model for HOMs, and also quantified rate and equilibrium constants for cyclic peroxyhemiacetal formation and the effects of particle acidity and relative humidity on reaction products and timescales for decomposition of peroxide-containing compounds. Sulfuric acid increased the rate of acetal formation and subsequent peroxide decomposition, but the effect was eliminated when aqueous seed particles were used in humid air, indicating that organic/aqueous phase separation can affect the ability of strong acids to catalyze these and other reactions in SOA. The results will be useful for understanding and predicting the atmospheric fate of organic peroxides and the effects of their particle-phase reactions on SOA composition.
A review of transfer theory and characterization of measured performance
for differential mobility analyzers
Mark R. Stolzenburg
Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, USA
ABSTRACT
Particle transfer theory for steady-state differential mobility analyzers (DMAs) with and without diffusion is reviewed in detail with a particular focus on the assumptions and approximations made in the analysis. Impacts of the approximations are discussed and, where available, methods to reduce the errors of these approximations are suggested. The nondiffusing theory uses just one approximation, affecting the centroid calculation, which can be readily addressed via numerical modeling of the electric field. The diffusing theory makes numerous approximations to achieve an analytical expression. One of the most serious of these, neglecting secondary flows in the vicinities of the aerosol entrance and exit slits, could be improved upon using a numerical model of the flow field. Losses in the aerosol entrance plumbing can perturb the inlet profile to the classification region. The maximum effects on the transfer function are estimated to be a 1% increase in the mean mobility and a 14% reduction of the nondiffusing contribution to the variance. Methods of fitting transfer theory to measurements are also reviewed. Tandem differential mobility analyzer measurements generally do not have the resolving power to distinguish different shapes of the transfer function but newer measurements using truly monomobile ions have the potential to more rigorously test the diffusive transfer model. In adjusting the width of the theoretical transfer function to fit measurements from a real DMA demonstrating nonideal performance, it is physically more meaningful and accurate to use an additive adjustment to the variance as opposed to a multiplicative adjustment to the width.
