Aerosol Sensor Research Articles

On-Line Analysis of Gas-Phase Composition in the Combustion Chamber and Particle Emission Characteristics during Combustion of Wood and Waste in a Small Batch Reactor

The emission of particulate matter and gaseous compounds during combustion of wood and refuse-derived fuel in a small batch reactor is investigated by laser mass-spectrometric on-line measurement techniques for gas-phase analysis and simultaneous registration of physical aerosol properties (number size distribution). The gas-phase composition is addressed by a laser-based mass spectrometric method, namely, vacuum-UV single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Particle-size distributions are measured with a scanning mobility particle sizer. Furthermore, a photoelectric aerosol sensor is applied for detection of particle-bound polycyclic aromatic hydrocarbons. The different phases of wood combustion are distinguishable by both the chemical profiles of gas-phase components (e.g., polycyclic aromatic hydrocarbons, PAH) and the particle-size distribution. Furthermore, short disturbances of the combustion process due to air supply shortages are investigated regarding their effect on particle-size distribution and gas-phase composition, respectively. It is shown that the combustion conditions strongly influence the particle-size distribution as well as on the emission of particle-bound polycyclic aromatic hydrocarbons.

Influence of a catalytic stripper on the response of real time aerosol instruments to diesel exhaust aerosol

The objective of this study was to evaluate the response of a suite of portable, real-time aerosol instruments to Diesel exhaust aerosol with and without a catalytic stripper (CS) to determine the change in response as a function of particle size and volatility. The response of the photoemission aerosol sensor (PAS) was strongly influenced by the physical and chemical nature of Diesel aerosol. The presence of a large, predominantly volatile nuclei mode, and/or the presence of volatile material on the surface of the solid carbonaceous agglomerates in the accumulation mode suppressed the PAS response. Removal of the volatile material by passage of the aerosol through the CS enhanced the response, and improved correlations between the PAS, the diffusion charger (DC) and the scanning mobility particle sizer (SMPS). Data on aerosol size distributions, number, volume, and surface area concentrations with and without the CS in the sample stream are reported.

Open photoacoustic sensor as smoke detector

We describe the use of a photoacoustic aerosol sensor for fire detection applications. The sensor is based on a cylindrical resonant chamber which is completely open on both sides in order to allow the smoke to enter it by pure diffusion. The sensor is equipped with a resonance tracking system that continuously monitors the changes in the resonance frequency caused by environmental conditions or an actual fire situation. The results show that our sensor has a very good response to smoke originating in open flaming combustion processes, which are hard to detect with commercially available sensors, and a low cross-sensitivity to the usual false alarm sources making it an ideal candidate to fill in an existing gap in the fire detection devices.

Eddy correlation measurements of aerosol deposition to grass

An experiment was conducted to measure aerosol turbulent fluxes to a grass field. A new high-flow-rate aerosol sensor was deployed from a tower to make eddy correlation (EC) measurements of aerosol turbulent flux and deposition velocity. The EC data were screened and analysed for uncertainties associated with advection, boundary layer growth, instrument separation and counting particles. An apparent bias in the aerosol flux due to particle hygroscopic growth was evaluated from chemical and microphysical measurements and removed from the results based on derived corrections. The resulting aerosol deposition velocity for 0.52 μm diameter particles depended on atmospheric stability with values of 0.3 cm s−1 during near-neutral stability, 0.44 cm s−1 during unstable periods and 0.16 cm s−1 during stable periods with an estimated uncertainty of ±0.07 cm s−1 due to chemical composition and particle counting.

The active surface of suspended particles as a predictor of lung function and pulmonary symptoms in Austrian school children

At a central elementary school in the capital of Upper Austria children aged 7–10 years underwent repeated respiratory health checkups (questionnaires, diaries, spirometry). Between March and May 2001 the daily means of the signals of a diffusion charging sensor, measuring the “active surface” of suspended particles, and a photoelectric aerosol sensor, measuring the particle-bound polycyclic aromatic hydrocarbons, were related to spirometric results of the total 164 children examined and to the daily symptom scores of a susceptible subgroup. Significant reductions of forced vital capacity ( p=0.006) and forced expiratory volume in the first second ( p=0.001) and significant increases of wheezing ( p=0.001), shortness of breath ( p=0.041), cough in the evening ( p=0.031) and at night ( p=0.018) were found with increase of “active surface” of suspended particles measured at the adjacent outdoor monitoring station, but not with the increase of particle-bound polycyclic aromatic hydrocarbons. Monitoring “active surface” of particles with diameters of about 10 nm–1 μm by means of a diffusion charging sensor might provide additional information in surveillance of particulate matter for prevention of acute effects on respiratory health.

Real-time characterization of ultrafine and accumulation mode particles in ambient combustion aerosols

The diffusion charging sensor (DC), photoelectric aerosol sensor (PAS) and condensation particle counter (CPC) are real-time particle instruments that have time resolutions <10 s and are suitable for field use. This paper shows how the relative fraction of nuclei mode particles (D⩽50 nm) in ambient combustion aerosols can be determined, along with the coverage degree of the respective accumulation mode particles with a modal diameter of ∼100 nm . Main tools for interpretation are the diameter of average surface D Ave, S (obtained from CPC and DC measurements) and PAS/DC versus D Ave, S scatter plots. Compared to the scanning mobility particle sizer (SMPS), which is a standard instrument for aerosol particle size distribution measurements, the presented method has a limited accuracy, but is substantially faster. Additionally, it is experimentally less demanding than SMPS measurements, especially for field applications.

A comparison of temporal variation of particle-bound polycyclic aromatic hydrocarbons (pPAHs) concentration in different urban environments: Tokyo, Japan, and Bangkok, Thailand

A comparative study of the real-time ambient concentrations of particle-bound polycyclic aromatic hydrocarbons (pPAHs) in the vicinity of roads in Tokyo (Japan) and in Bangkok (Thailand) in summertime was carried out by using a photoelectric aerosol sensor (PAS), which gives continuous signal in relation to the total amount of pPAHs concentration. The PAS output gave a good correlation to the total concentration of the selected PAHs determined by gas chromatography/mass spectrometry (GC/MS). This technique was then employed to observe temporal variation of total pPAHs. The measurements at roadside and general areas in Tokyo and in Bangkok were performed for seven consecutive days in August 2000, and in March 2001, respectively. The diurnal profiles of pPAHs concentrations in both cities were generally similar; explicit peak concentrations were observed in early morning in association with the traffic growth in the morning rush hours. A significant reduction occurred during the daytime was probably due to rising in the mixing zone. At roadside areas, the average pPAHs concentrations throughout the sampling period in Bangkok were significantly higher than those of Tokyo, owing to the larger contribution of vehicular traffic, especially heavy-duty vehicles, on the roads near the sampling site. Otherwise, all average concentrations in the general area in Tokyo were slightly higher than that of Bangkok. This was probably due to the percentage of road coverage in Tokyo being higher than that in Bangkok, creating a higher possibility for pPAHs evolving from road traffic, and the transportation pattern of the pPAHs in Tokyo showed a more broadly diffused profile than that of Bangkok. This suggests the widespread dispersion of pPAHs over the entire study area in Tokyo. At this study scale especially at the roadside, however, a high pPAHs concentration observed in Tokyo and in Bangkok was predominantly located at low wind speed, <1.0 and 0.4 m s −1, respectively, and along the direction from the roads.

Diurnal Profile of Particle-bound Polycyclic Aromatic Hydrocarbon (pPAH) Concentration in Urban Environment in Tokyo Metropolitan Area

Traffic emits particles under 1 μm. The particles arethe most responsible to particle-bound polycyclic aromatichydrocarbon (pPAH) which can impact human health. To assessthem as health hazards, we monitored diurnal changes in theconcentration and distribution of pPAH near roads in Tokyo.The total pPAH concentration was determined using aphotoelectric aerosol sensor (PAS) which ionized PAH-adsorbingparticles. The total pPAH concentration was compared withchemical analyses by gas chromatography/mass spectrometry(GC/MS). Two sampling sessions, one in August and one inSeptember 2000, were done at three sampling sites at the Hongo Campus of the University of Tokyo. Monitoring was every two minutes for six consecutive days for the first session and for seven consecutive days for the second session.Correlation of the pPAH concentration with traffic flow andwith meteorological conditions were also assessed. The pPAHconcentration varied in the same manner on all days: it sharplyincreased in the early morning by a sudden burden of traffic, and it rapidly decreased during the daytime, probably owing tophotodegradation and/or dilution by rising in the mixingzone. The local wind field, and consequently thetransportation of pPAH from the road, were stronglyinfluenced by the configuration and location of thesurrounding buildings. The pPAH clearly changed in 1- and0.5 day cycles, particularly at the roadside.

Estimating the contributions of mobile sources of PAH to urban air using real-time PAH monitoring

Motor vehicles are a significant source of airborne polycyclic aromatic hydrocarbons (PAH) in many urban areas. Traditional approaches used in determining the relative contributions of individual vehicle types to the total amount of PAH in air have been based on the analysis of integrated samples of airborne particles and gases for the presence of chemical tracers indicative of the vehicles from which the chemicals derived. As an alternative, we have used a photoelectric aerosol sensor (PAS) capable of measuring PAH levels in real-time in the emissions plumes from motor vehicles. We placed the PAS near a traffic-light in Kenmore Square, a busy crossroads in downtown Boston (MA, USA). A video camera co-located at the site recorded the vehicles passing the sensor, and this record was correlated with the PAS data. During a 5-day monitoring period (∼59 h) in the summer of 1998, over 34 000 motor vehicles were counted and classified and over 24 000 PAS readings were recorded (frequency=1/8.6 s). The composition of the vehicle population was 94% passenger vehicles, 1.4% buses, 2.6% small trucks, 1.3% medium trucks, 0.35% large trucks, and 0.45% garbage and construction trucks. In analyzing the PAS data, it was assumed that the highest PAS measurements — those that exceeded the 95% critical level of the 5-min moving average of all the PAS measurements — were indicative of primary vehicular emissions. We found that ∼46% of the mass of particle-bound PAH (i.e. ∼46% of the integrated area under the PAS signal vs. time plots) was attributable to primary emissions from motor vehicles passing the sensor. Of this, 35–61% was attributable to passenger vehicles (cars, pickup trucks, and sports utility vehicles) and 39–65% was attributable to non-passenger vehicles [buses (14–23%), small trucks (12–20%), medium trucks (8.4–14%), large trucks (2.9–4.8%) and garbage and construction trucks (1.9–3.2%)]. Our results suggest that on a per vehicle basis, buses and trucks — the majority of which run on diesel fuel — emitted greater amounts of particle-bound PAH than passenger vehicles. Overall, we found that real-time photoelectric aerosol sensing (in combination with video photography) is useful for estimating the contributions of airborne PAH from different vehicle types. Due to the physical constraints of our monitoring site and the high volumes of traffic, however, it was not possible to uniquely attribute PAS signals to individual vehicles.

Testing Re-entrained Aerosol Kinetic Emissions from Roads : a new approach to infer silt loading on roadways

PM 10 and PM 2.5 emissions from roadways are currently estimated using the silt loading on the road surface as a surrogate for the emissions potential of road dust. While the United States Environmental Protection Agency prescribes this method in AP-42, there is considerable cost associated with silt loading measurements; it is feasible to sample only a small portion of a roadway network. A new approach for measuring the concentration of suspendable PM 10 above road surfaces has been developed to obtain a more spatially representative estimate of a road's potential to emit dust. The Testing Re-entrained Aerosols Kinetic Emissions from Roads (TRAKER) system uses real-time aerosol sensors mounted on a vehicle to measure the concentration of dust suspended from the road while the vehicle is in motion. When coupled with a Global Positioning System (GPS) instrument, TRAKER can be used to efficiently survey the changes in suspendable particles due to varying road conditions over a large spatial domain. In a recent study on paved roads in Las Vegas, the TRAKER system was compared with collocated silt loading measurements. The TRAKER system was also used to survey the relative amounts of suspendable road dust on approximately 300 miles of paved roads. The system provides a unique perspective on road dust sources and their spatial distribution. Results of this study indicated that the difference of the PM 10 concentrations measured behind the tire and on the hood is exponentially related to vehicle speed. This was an interesting finding because current AP-42 road dust emissions estimation methods do not include vehicle speed as a factor in the emissions calculations. The experiment also demonstrated that the distribution of suspendable material on roadways is highly variable and that a large number of samples are needed to represent road dust emissions potential on an urban scale for a variety of road and activity conditions.

Use of Continuous Measurements of Integral Aerosol Parameters to Estimate Particle Surface Area

While surface area is one of the most important atmospheric aerosol properties in health effects, methods for online measurement of surface area are not widely available and/or require complex operations. In this paper, we describe an integrated measurement method that can continuously monitor the total surface area, as well as the total number and volume, of atmospheric aerosols. Three integral aerosol sensors - (i) a condensation particle counter (CPC) for number concentration measurement, (ii) a mass concentration monitor (MCM) for mass concentration measurement, and (iii) an electrical aerosol detector (EAD) for current measurement of charged aerosol - are used in this study. Signals from the three sensors are converted into a lognormal size distribution by minimizing the difference between the measured signals and the theoretical values based upon a size distribution model, the instrument calibration, and its theoretical responses. Results from a 20 day continuous sampling period show that the calculated total surface area from integrated measurement correlates well with that of particle sizing measurement. The calculated lognormal size distribution parameters between the two methods have similar values. These results suggest that the integrated measurement method is feasible to continuously measure total number, surface area, and volume concentrations. As the integrated measurement method can yield results in near real time, it can be used for online measurement of atmospheric aerosols.

Use of Continuous Measurements of Integral Aerosol Parameters to Estimate Particle Surface Area

While surface area is one of the most important atmospheric aerosol properties in health effects, methods for online measurement of surface area are not widely available and/or require complex operations. In this paper, we describe an integrated measurement method that can continuously monitor the total surface area, as well as the total number and volume, of atmospheric aerosols. Three integral aerosol sensors - (i) a condensation particle counter (CPC) for number concentration measurement, (ii) a mass concentration monitor (MCM) for mass concentration measurement, and (iii) an electrical aerosol detector (EAD) for current measurement of charged aerosol - are used in this study. Signals from the three sensors are converted into a lognormal size distribution by minimizing the difference between the measured signals and the theoretical values based upon a size distribution model, the instrument calibration, and its theoretical responses. Results from a 20 day continuous sampling period show that the calcul...

Real-Time and Integrated Measurement of Potential Human Exposure to Particle-Bound Polycyclic Aromatic Hydrocarbons (PAHs) from Aircraft Exhaust

We used real-time monitors and low-volume air samplers to measure the potential human exposure to airborne polycyclic aromatic hydrocarbon (PAH) concentrations during various flight-related and ground-support activities of C-130H aircraft at an Air National Guard base. We used three types of photoelectric aerosol sensors (PASs) to measure real-time concentrations of particle-bound PAHs in a break room, downwind from a C-130H aircraft during a four-engine run-up test, in a maintenance hangar, in a C-130H aircraft cargo bay during cargo-drop training, downwind from aerospace ground equipment (AGE), and in a C-130H aircraft cargo bay during engine running on/off (ERO) loading and backup exercises. Two low-volume air samplers were collocated with the real-time monitors for all monitoring events except those in the break room and during in-flight activities. Total PAH concentrations in the integrated-air samples followed a general trend: downwind from two AGE units > ERO-loading exercise > four-engine run-up test > maintenance hangar during taxi and takeoff > background measurements in maintenance hangar. Each PAH profile was dominated by naphthalene, the alkyl-substituted naphthalenes, and other PAHs expected to be in the vapor phase. We also found particle-bound PAHs, such as fluoranthene, pyrene, and benzo[a]pyrene in some of the sample extracts. During flight-related exercises, total PAH concentrations in the integrated-air samples were 10-25 times higher than those commonly found in ambient air. Real-time monitor mean responses generally followed the integrated-air sample trends. These monitors provided a semiquantitative temporal profile of ambient PAH concentrations and showed that PAH concentrations can fluctuate rapidly from a baseline level < 20 to > 4,000 ng/m(3) during flight-related activities. Small handheld models of the PAS monitors exhibited potential for assessing incidental personal exposure to particle-bound PAHs in engine exhaust and for serving as a real-time dosimeter to indicate when respiratory protection is advisable.

Real-time and integrated measurement of potential human exposure to particle-bound polycyclic aromatic hydrocarbons (PAHs) from aircraft exhaust.

We used real-time monitors and low-volume air samplers to measure the potential human exposure to airborne polycyclic aromatic hydrocarbon (PAH) concentrations during various flight-related and ground-support activities of C-130H aircraft at an Air National Guard base. We used three types of photoelectric aerosol sensors (PASs) to measure real-time concentrations of particle-bound PAHs in a break room, downwind from a C-130H aircraft during a four-engine run-up test, in a maintenance hangar, in a C-130H aircraft cargo bay during cargo-drop training, downwind from aerospace ground equipment (AGE), and in a C-130H aircraft cargo bay during engine running on/off (ERO) loading and backup exercises. Two low-volume air samplers were collocated with the real-time monitors for all monitoring events except those in the break room and during in-flight activities. Total PAH concentrations in the integrated-air samples followed a general trend: downwind from two AGE units > ERO-loading exercise > four-engine run-up test > maintenance hangar during taxi and takeoff > background measurements in maintenance hangar. Each PAH profile was dominated by naphthalene, the alkyl-substituted naphthalenes, and other PAHs expected to be in the vapor phase. We also found particle-bound PAHs, such as fluoranthene, pyrene, and benzo[a]pyrene in some of the sample extracts. During flight-related exercises, total PAH concentrations in the integrated-air samples were 10-25 times higher than those commonly found in ambient air. Real-time monitor mean responses generally followed the integrated-air sample trends. These monitors provided a semiquantitative temporal profile of ambient PAH concentrations and showed that PAH concentrations can fluctuate rapidly from a baseline level < 20 to > 4,000 ng/m(3) during flight-related activities. Small handheld models of the PAS monitors exhibited potential for assessing incidental personal exposure to particle-bound PAHs in engine exhaust and for serving as a real-time dosimeter to indicate when respiratory protection is advisable.

Acoustic aerosol sensor

The paper concerns the acoustic measurement of aerosol concentration using the resonance absorption effect. This effect shows a high sensitivity to the variation of the mass concentration of the liquid component of an aerosol. Basing on this effect, development, design and calibration of an acoustic aerosol sensor are described. This sensor is provided for online measurements of high concentrated aerosols.

The contribution of traffic to indoor concentrations of polycyclic aromatic hydrocarbons.

A photoelectric aerosol sensor (PAS) was used to measure real-time indoor concentrations of polycyclic aromatic hydrocarbons (PAHs) at three residences. Semi-quantitative measurements of total indoor particle-bound PAH and temperature were collected continuously every minute for approximately 2 weeks at each location. The purpose of this study was to examine the effect of traffic on indoor concentrations of PAHs. This was accomplished by collecting indoor measurements at an urban, semi-urban, and suburban residential location with varying levels of, and proximity to, traffic. Since the homes were occupied, the effects of cooking, the dominant indoor source, were also examined among the three nonsmoking households. The results indicate that traffic was the main outdoor source of PAH concentrations measured indoors for all locations. In fact, a significant (p<0.001) traffic-related trend in weekday PAH concentration was detected with a geometric mean concentration at the urban location (31 ng/m3) nearly two times that at the semi-urban location (19 ng/m3) and over three times larger than the suburban location (8.0 ng/m3), once adjusted for indoor sources. Hourly average concentration profiles also revealed weekday rush hour peaks of PAHs at all locations. No pronounced peaks and significantly lower concentrations (10, 10, and 4.9 ng/m3) were seen during the weekends for all locations i.e., the urban, semi-urban and suburban locations, respectively. Indoor sources including frying/sautéing, broiling, and candle-burning were characterized by peak concentration, duration of PAH elevation, and potential dose. This analysis suggests that cooking, and especially frying/sautéing, may be an important source of indoor PAH concentrations.

Determination of Air Exchange Rates of Rooms and Deposition Factors for Fine Particles by Means of Photoelectric Aerosol Sensors

Indoor and outdoor concentrations of airborne fine particles from internal combustion engines have been measured over periods of 24 h with a time resolution of 10 s. With this time series, the ventilation air exchange rate of different rooms has been computed using a novel approach to the solution of the mass balance equation. A ‘mixing time’ parameter has been introduced in order to account for the initial non-homogeneous distribution of the pollutants in the rooms. It is demonstrated that this method can be used to determine the impact of health-relevant outdoor particles on the indoor particle concentration. This yields information on the protection a building offers against pollutants entering from outdoors.

Determination of Air Exchange Rates of Rooms and Deposition Factors for Fine Particles by Means of Photoelectric Aerosol Sensors

Indoor and outdoor concentrations of airborne fine parti cles from internal combustion engines have been mea sured over periods of 24 h with a time resolution of 10 s. With this time series, the ventilation air exchange rate of different rooms has been computed using a novel ap proach to the solution of the mass balance equation. A 'mixing time' parameter has been introduced in order to account for the initial non-homogeneous distribution of the pollutants in the rooms. It is demonstrated that this method can be used to determine the impact of health- relevant outdoor particles on the indoor particle concen tration. This yields information on the protection a build ing offers against pollutants entering from outdoors.

Dynamic Field Measurements of Submicron Particles from Diesel Engines

We present new tools and a complete setup with which the submicron particles, emitted from combustion processes, can be measured and classified according to their chemical nature even in the field. Diesel engines are the predominant source of these particles in the industrialized countries. The setup comprises an exhaust conditioning part including means for precipitation of the coarse particle fraction, dilution, and removal of volatile material. The submicron particles are detected with three different sensors: one for particle number concentration (condensation particle counter, CPC), one for the particle “Fuchs”-surface (diffusion charger, DC), and one that responds specifically to the carbonaceous particles (photoelectric aerosol sensor, PAS). These sensors possess a short response time so that transients such as those occurring in the free acceleration mode may be observed as well. Experiments on a conventional engine test bench demonstrate the tools. The test results are highly reassuring. Correct handling of the volatile fraction is essential to avoid severe artifacts from gas to particle reactions particularly in exhaust from engines equipped with particle traps.

Correlation between On-Line PAH Detection in Airbone Particle Samples and Their Bacterial Genotoxicity

The photoelectric aerosol sensor (PAS) is a technique suitable for on-line monitoring of particle-bound polycyclic aromatic hydrocarbons (PPAHs). Although this is a very fast and inexpensive technique, it does not measure individual PAH species but gives a measure of the total amount of PPAHs. Because of the suitability of this sensor for air-pollution screening, it is desirable to know whether a correlation exists between the PPAHs detected with this method and the biological relevance of the respective particle samples. To test the DNA damaging potential of the organic fraction of collected particles, the umuC test withSalmonella typhimuriumTA1535/pSK1002 was used. The primary source for particle sampling was a stationary diesel engine, but samples from a parking garage and two locations in the city of Zürich have also been included. The total mass of PPAHs as determined by the PAS was plotted against the induced genotoxicity. This resulted in a linear correlation (r2=0.82), indicating that the PAS detects biologically relevant PPAHs.