scholarly journals Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry: results from the CENICA Supersite

2006 ◽  
Vol 6 (4) ◽  
pp. 925-946 ◽  
Author(s):  
D. Salcedo ◽  
T. B. Onasch ◽  
K. Dzepina ◽  
M. R. Canagaratna ◽  
Q. Zhang ◽  
...  
Keyword(s):  
Mexico City ◽  
Mass Concentration ◽  
Inorganic Compounds ◽  
Regional Scale ◽  
Soil Mass ◽  
Emission Spectrometry ◽  
Size Distributions ◽  
Pixe Analysis ◽  
Aerosol Mass ◽  
Inorganic Species

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite, during the Mexico City Metropolitan Area field study (MCMA-2003) from 31 March-4 May 2003 to investigate particle concentrations, sources, and processes. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM1) with high time and size-resolution. In order to account for the refractory material in the aerosol, we also present estimates of Black Carbon (BC) using an aethalometer and an estimate of the aerosol soil component obtained from Proton-Induced X-ray Emission Spectrometry (PIXE) analysis of impactor substrates. Comparisons of AMS + BC + soil mass concentration with other collocated particle instruments (a LASAIR Optical Particle Counter, a PM2.5 Tapered Element Oscillating Microbalance (TEOM), and a PM2.5 DustTrak Aerosol Monitor) show that the AMS + BC + soil mass concentration is consistent with the total PM2.5 mass concentration during MCMA-2003 within the combined uncertainties. In Mexico City, the organic fraction of the estimated PM2.5 at CENICA represents, on average, 54.6% (standard deviation σ=10%) of the mass, with the rest consisting of inorganic compounds (mainly ammonium nitrate and sulfate/ammonium salts), BC, and soil. Inorganic compounds represent 27.5% of PM2.5 (σ=10%); BC mass concentration is about 11% (σ=4%); while soil represents about 6.9% (σ=4%). Size distributions are presented for the AMS species; they show an accumulation mode that contains mainly oxygenated organic and secondary inorganic compounds. The organic size distributions also contain a small organic particle mode that is likely indicative of fresh traffic emissions; small particle modes exist for the inorganic species as well. Evidence suggests that the organic and inorganic species are not always internally mixed, especially in the small modes. The aerosol seems to be neutralized most of the time; however, there were some periods when there was not enough ammonium to completely neutralize the nitrate, chloride and sulfate present. The diurnal cycle and size distributions of nitrate suggest local photochemical production. On the other hand, sulfate appears to be produced on a regional scale. There are indications of new particle formation and growth events when concentrations of SO2 were high. Although the sources of chloride are not clear, this species seems to condense as ammonium chloride early in the morning and to evaporate as the temperature increases and RH decreases. The total and speciated mass concentrations and diurnal cycles measured during MCMA-2003 are similar to measurements during a previous field campaign at a nearby location.

scholarly journals Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry – Part I: quantification, shape-related collection efficiency, and comparison with collocated instruments

2005 ◽  
Vol 5 (3) ◽  
pp. 4143-4182 ◽  
Author(s):  
D. Salcedo ◽  
K. Dzepina ◽  
T. B. Onasch ◽  
M. R. Canagaratna ◽  
Q. Zhang ◽  
...  
Keyword(s):  
Mexico City ◽  
Mass Concentration ◽  
Collection Efficiency ◽  
Beam Width ◽  
Soil Mass ◽  
Emission Spectrometry ◽  
Ambient Aerosols ◽  
Pixe Analysis ◽  
Aerosol Mass ◽  
Beam Broadening

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite, while another was deployed in the Aerodyne Mobile Laboratory (AML) during the Mexico City Metropolitan Area field study (MCMA-2003) from 31 March–4 May 2003 to investigate particle concentrations, sources, and processes. This is the first of a series of papers reporting the AMS results from this campaign. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM1) with high time and size-resolution. For the first time, we report field results from a beam width probe, which was used to study the shape and mixing state of the particles and to quantify potential losses of irregular particles due to beam broadening inside the AMS. Data from this probe show that no significant amount of irregular particles was lost due to excessive beam broadening. A comparison of the CENICA and AML AMSs measurements is presented, being the first published intercomparison between two quadrupole AMSs. The speciation, and mass concentrations reported by the two AMSs compared relatively well. The differences found are likely due to the different inlets used in both instruments. In order to account for the refractory material in the aerosol, we also present measurements of Black Carbon (BC) using an aethalometer and an estimate of the aerosol soil component obtained from Proton-Induced X-ray Emission Spectrometry (PIXE) analysis of impactor substrates. Comparisons of AMS + BC + soil mass concentration with other collocated particle instruments (a LASAIR Optical Particle Counter, a Tapered Element Oscillating Microbalance (TEOM) and a DustTrak Aerosol Monitor) are also presented. The comparisons show that the AMS + BC + soil mass concentration during MCMA-2003 is a good approximation to the total PM2.5 mass concentration.

scholarly journals Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry – Part II: overview of the results at the CENICA supersite and comparison to previous studies

2005 ◽  
Vol 5 (3) ◽  
pp. 4183-4221 ◽  
Author(s):  
D. Salcedo ◽  
K. Dzepina ◽  
T. B. Onasch ◽  
M. R. Canagaratna ◽  
J. T. Jayne ◽  
...  
Keyword(s):  
Mexico City ◽  
Mass Concentration ◽  
Inorganic Compounds ◽  
Field Measurements ◽  
Size Distributions ◽  
Ambient Aerosols ◽  
Pixe Analysis ◽  
Diurnal Cycles ◽  
Aerosol Mass ◽  
Boundary Layer Dynamics

Abstract. An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite during the Mexico City Metropolitan Area field study from 31 March–4 May 2003. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM1) with high time and size-resolution. Measurements of Black Carbon (BC) using an aethalometer, and estimated soil concentrations from Proton-Induced X-Ray Emission (PIXE) analysis of impactor substrates are also presented and combined with the AMS in order to include refractory material and estimate the total PM2.5 mass concentration at CENICA during this campaign. In Mexico City, the organic fraction of the estimated PM2.5 at CENICA represents 54.6% of the mass, with the rest consisting of inorganic compounds (mainly ammonium nitrate and sulfate/ammonium salts), BC, and soil. Inorganic compounds represent 27.5% of PM2.5; BC mass concentration is about 11%; while soil represents about 6.9%. The NR species and BC have diurnal cycles that can be qualitatively interpreted as the interplay of direct emissions, photochemical production in the atmosphere followed by condensation and gas-to-particle partitioning, boundary layer dynamics, and/or advection. Bi- and trimodal size distributions are observed for the AMS species, with a small combustion (likely traffic) organic particle mode and an accumulation mode that contains mainly organic and secondary inorganic compounds. The AMS and BC mass concentrations, size distributions, and diurnal cycles are found to be qualitatively similar to those from most previous field measurements in Mexico City.

scholarly journals Characterization of near-highway submicron aerosols in New York City with a high-resolution aerosol mass spectrometer

2012 ◽  
Vol 12 (4) ◽  
pp. 2215-2227 ◽  
Author(s):  
Y. L. Sun ◽  
Q. Zhang ◽  
J. J. Schwab ◽  
W.-N. Chen ◽  
M.-S. Bae ◽  
...  
Keyword(s):  
New York ◽  
New York City ◽  
Chemical Composition ◽  
High Resolution ◽  
York City ◽  
Size Distributions ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Inorganic Species

Abstract. Knowledge of the variations of mass concentration, chemical composition and size distributions of submicron aerosols near roadways is of importance for reducing exposure assessment uncertainties in health effects studies. The goal of this study is to deploy and evaluate an Atmospheric Sciences Research Center-Mobile Laboratory (ASRC-ML), equipped with a suite of rapid response instruments for characterization of traffic plumes, adjacent to the Long Island Expressway (LIE) – a high-traffic highway in the New York City Metropolitan Area. In total, four measurement periods, two in the morning and two in the evening were conducted at a location approximately 30 m south of the LIE. The mass concentrations and size distributions of non-refractory submicron aerosol (NR-PM1) species were measured in situ at a time resolution of 1 min by an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer, along with rapid measurements (down to 1 Hz) of gaseous pollutants (e.g. HCHO, NO2, NO, O3, and CO2, etc.), black carbon (BC), and particle number concentrations and size distributions. Particulate organics varied dramatically during periods with high traffic influences from the nearby roadway. The variations were mainly observed in the hydrocarbon-like organic aerosol (HOA), a surrogate for primary OA from vehicle emissions. The inorganic species (sulfate, ammonium, and nitrate) and oxygenated OA (OOA) showed much smoother variations indicating minor impacts from traffic emissions. The concentration and chemical composition of NR-PM1 also varied differently on different days depending on meteorology, traffic intensity and vehicle types. Overall, organics dominated the traffic-related NR-PM1 composition (>60%) with HOA accounting for a major fraction of OA. The traffic-influenced organics showed two distinct modes in mass-weighted size distributions, peaking at ∼120 nm and 500 nm (vacuum aerodynamic diameter, Dva), respectively. OOA and inorganic species appear to be internally mixed in the accumulation mode peaking at ∼500–600 nm. The enhancement of organics in traffic emissions mainly occurred at ultrafine mode dominated by HOA, with little relation to the OOA-dominated accumulation mode. From Fast Mobility Particle Sizer (FMPS) measurements, a large increase in number concentration at ∼10 nm (mobility number mean diameter, Dm) was also found due to traffic influence; though these particles typically contribute a minor fraction of total particle mass. The observed rapid variations of aerosol chemistry and microphysics may have significant implications for near-highway air pollution characterization and exposure assessments.

scholarly journals Evaluation of the new capture vapourizer for aerosol mass spectrometers (AMS) through laboratory studies of inorganic species

2017 ◽  
Vol 10 (8) ◽  
pp. 2897-2921 ◽  
Author(s):  
Weiwei Hu ◽  
Pedro Campuzano-Jost ◽  
Douglas A. Day ◽  
Philip Croteau ◽  
Manjula R. Canagaratna ◽  
...  
Keyword(s):  
Collection Efficiency ◽  
Submicron Particles ◽  
Size Distributions ◽  
Volatile Species ◽  
Pure Species ◽  
Mass Spectrometers ◽  
Aerosol Mass ◽  
Aerosol Mass Concentration ◽  
Inorganic Species ◽  
Multiple Collisions

Abstract. Aerosol mass spectrometers (AMSs) and Aerosol Chemical Speciation Monitors (ACSMs) commercialized by Aerodyne are widely used to measure the non-refractory species in submicron particles. With the standard vapourizer (SV) that is installed in all commercial instruments to date, the quantification of ambient aerosol mass concentration requires the use of the collection efficiency (CE) to correct for the loss of particles due to bounce. A new capture vapourizer (CV) has been designed to reduce the need for a bounce-related CE correction. Two high-resolution AMS instruments, one with a SV and one with a CV, were operated side by side in the laboratory. Four standard species, NH4NO3, NaNO3, (NH4)2SO4 and NH4Cl, which typically constitute the majority of the mass of ambient submicron inorganic species, are studied. The effect of vapourizer temperature (Tv ∼ 200–800 °C) on the detected fragments, CE and size distributions are investigated. A Tv of 500–550 °C for the CV is recommended. In the CV, CE was identical (around unity) for more volatile species (e.g. NH4NO3) and comparable to or higher than the SV for less-volatile species (e.g. (NH4)2SO4), demonstrating an improvement in CE for laboratory inorganic species in the CV. The detected relative intensities of fragments of NO3 and SO4 species observed with the CV are different from those observed with the SV, and are consistent with additional thermal decomposition arising from the increased residence time and multiple collisions. Increased residence times with the CV also lead to broader particle size distribution measurements than with the SV. A method for estimating whether pure species will be detected in AMS sizing mode is proposed. Production of CO2(g) from sampled nitrate on the vapourizer surface, which has been reported for the SV, is negligible for the CV for NH4NO3 and comparable to the SV for NaNO3. . We observe an extremely consistent fragmentation for ammonium compared to very large changes for the associated anions. Together with other evidence, this indicates that it is unlikely that a major fraction of inorganic species vapourizes as intact salts in the AMS.

scholarly journals Vertical distribution of aerosols in the vicinity of Mexico City during MILAGRO-2006 Campaign

2010 ◽  
Vol 10 (3) ◽  
pp. 1017-1030 ◽  
Author(s):  
P. A. Lewandowski ◽  
W. E. Eichinger ◽  
H. Holder ◽  
J. Prueger ◽  
J. Wang ◽  
...  
Keyword(s):  
Size Distribution ◽  
Mexico City ◽  
Mass Concentration ◽  
Heavy Traffic ◽  
Aerosol Size Distribution ◽  
Lidar System ◽  
Aerosol Mass ◽  
Aerosol Mass Concentration ◽  
Lidar Measurements ◽  
Ground Based Lidar

Abstract. On 7 March 2006, a mobile, ground-based, vertical pointing, elastic lidar system made a North-South transect through the Mexico City basin. Column averaged, aerosol size distribution (ASD) measurements were made on the ground concurrently with the lidar measurements. The ASD ground measurements allowed calculation of the column averaged mass extinction efficiency (MEE) for the lidar system (1064 nm). The value of column averaged MEE was combined with spatially resolved lidar extinction coefficients to produce total aerosol mass concentration estimates with the resolution of the lidar (1.5 m vertical spatial and 1 s temporal). Airborne ASD measurements from DOE G-1 aircraft made later in the day on 7 March 2006, allowed the evaluation of the assumptions of constant ASD with height and time used for estimating the column averaged MEE. The results showed that the aerosol loading within the basin is about twice what is observed outside of the basin. The total aerosol base concentrations observed in the basin are of the order of 200 μg/m3 and the base levels outside are of the order of 100 μg/m3. The local heavy traffic events can introduce aerosol levels near the ground as high as 900 μg/m3. The article presents the methodology for estimating aerosol mass concentration from mobile, ground-based lidar measurements in combination with aerosol size distribution measurements. An uncertainty analysis of the methodology is also presented.

scholarly journals Comparing the Respirable Aerosol Concentrations and Particle Size Distributions Generated by Singing, Speaking and Breathing

2020 ◽  
Author(s):  
Jonathan Reid
Keyword(s):  
Economic Activity ◽  
Mass Concentration ◽  
Dynamic Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
High Profile ◽  
Aerosol Generation ◽  
Aerosol Mass ◽  
Significant Difference ◽  
Cultural Sector

<p>The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has resulted in an unprecedented shutdown in social and economic activity with the cultural sector particularly severely affected. Restrictions on performance have arisen from a perception that there is a significantly higher risk of aerosol production from singing than speaking based upon high-profile examples of clusters of COVID-19 following choral rehearsals. However, no direct comparison of aerosol generation from singing and speaking has been reported. Here, we measure aerosols from singing, speaking and breathing in a zero-background environment, allowing unequivocal attribution of aerosol production to specific vocalisations. Speaking and singing show steep increases in mass concentration with increase in volume (spanning a factor of 20-30 across the dynamic range measured, <i>p</i><1×10<sup>-5</sup>). At the quietest volume (50 to 60 dB), neither singing (<i>p</i>=0.19) or speaking (<i>p</i>=0.20) were significantly different to breathing. At the loudest volume (90 to 100 dB), a statistically significant difference (<i>p</i><1×10<sup>-5</sup>) is observed between singing and speaking, but with singing only generating a factor of between 1.5 and 3.4 more aerosol mass. Guidelines should create recommendations based on the volume and duration of the vocalisation, the number of participants and the environment in which the activity occurs, rather than the type of vocalisation. Mitigations such as the use of amplification and increased attention to ventilation should be employed where practicable. </p>

scholarly journals Characterization of near-highway submicron aerosols in New York City with a high-resolution time-of-flight aerosol mass spectrometer

2011 ◽  
Vol 11 (11) ◽  
pp. 30719-30755
Author(s):  
Y. L. Sun ◽  
Q. Zhang ◽  
J. J. Schwab ◽  
W.-N. Chen ◽  
M.-S. Bae ◽  
...  
Keyword(s):  
New York ◽  
New York City ◽  
Chemical Composition ◽  
High Resolution ◽  
Size Distributions ◽  
Resolution Time ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Inorganic Species

Abstract. Knowledge of the variations of mass concentration, chemical composition and size distributions of submicron aerosols near roadways is of importance for reducing exposure assessment uncertainties in health effects studies. The goal of this study is to deploy and evaluate an Atmospheric Sciences Research Center-Mobile Laboratory (ASRC-ML), equipped with a suite of rapid response instruments for characterization of traffic plumes, adjacent to the Long Island Expressway (LIE) – a high-traffic highway in the New York City Metropolitan Area. In total, four measurement periods, two in the morning and two in the evening were conducted at a location approximately 30 m south of the LIE. The mass concentrations and size distributions of non-refractory submicron aerosol (NR-PM1) species were measured in situ at a time resolution of 1 min by an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer, along with rapid measurements (down to 1 Hz) of gaseous pollutants (e.g., HCHO, NO2, NO, O3, and CO2, etc.), black carbon (BC), and particle number concentrations and size distributions. The particulate organics varied dramatically during periods with highest traffic influences from the nearby roadway. The variations were mainly observed in the hydrocarbon-like organic aerosol (HOA), a surrogate for primary OA from vehicle emissions. The inorganic species (sulfate, ammonium, and nitrate) and oxygenated OA (OOA) showed much smoother variations – with minor impacts from traffic emissions. The concentration and chemical composition of NR-PM1 also varied differently on different days depending on meteorology, traffic intensity and vehicle types. Overall, organics dominated the traffic-related NR-PM1 composition (>60%) with HOA being the major fraction of OA. The traffic-influenced organics showed two distinct modes in mass-weighted size distributions, peaking at ~120 nm and 500 nm (vacuum aerodynamic diameter, Dva), respectively. OOA and inorganic species appear to be internally mixed in the accumulation mode peaking at ~500–600 nm. The enhancement of organics in traffic emissions mainly occurred at ultrafine mode dominated by HOA, with little relation to the OOA-dominated accumulation mode. From Fast Mobility Particle Sizer (FMPS)measurements, a large increase in number concentration at ~10 nm (mobility number mean diameter, Dm) was also found due to traffic influence; though these particles typically contribute a minor fraction of total particle mass. Results here may have significant implications for near-highway air pollution characterization and exposure assessments. Our results suggest that exposure assessments must take into account the rapid variations of aerosol chemistry over short distances near roadways, and also that long-term monitoring of air pollutants throughout the day on different types of days is necessary to accurately gauge exposure to individuals.

scholarly journals Technical Note: Use of a beam width probe in an Aerosol Mass Spectrometer to monitor particle collection efficiency in the field

2007 ◽  
Vol 7 (2) ◽  
pp. 549-556 ◽  
Author(s):  
D. Salcedo ◽  
T. B. Onasch ◽  
M. R. Canagaratna ◽  
K. Dzepina ◽  
J. A. Huffman ◽  
...  
Keyword(s):  
Particle Size ◽  
Mexico City ◽  
Particle Shape ◽  
Collection Efficiency ◽  
Beam Width ◽  
Particle Beam ◽  
Aerosol Mass ◽  
Inorganic Species ◽  
Shape And Size ◽  
Beam Broadening

Abstract. Two Aerodyne Aerosol Mass Spectrometers (Q-AMS) were deployed in Mexico City, during the Mexico City Metropolitan Area field study (MCMA-2003) from 29 March–4 May 2003 to investigate particle concentrations, sources, and processes. We report the use of a particle beam width probe (BWP) in the field to quantify potential losses of particles due to beam broadening inside the AMS caused by particle shape (nonsphericity) and particle size. Data from this probe show that no significant mass of particles was lost due to excessive beam broadening; i.e. the shape- and size-related collection efficiency (Es) of the AMS during this campaign was approximately one. Comparison of the BWP data from MCMA-2003 with other campaigns shows that the same conclusion holds for several other urban, rural and remotes sites. This means that the aerodynamic lens in the AMS is capable of efficiently focusing ambient particles into a well defined beam and onto the AMS vaporizer for particles sampled in a wide variety of environments. All the species measured by the AMS during MCMA-2003 have similar attenuation profiles which suggests that the particles that dominate the mass concentration were internally mixed most of the time. Only for the smaller particles (especially below 300 nm), organic and inorganic species show different attenuation versus particle size which is likely due to partial external mixing of these components. Changes observed in the focusing of the particle beam in time can be attributed, in part, to changes in particle shape (i.e. due to relative humidity) and size of the particles sampled. However, the relationships between composition, atmospheric conditions, and particle shape and size appear to be very complex and are not yet completely understood.

scholarly journals Characterization of submicron aerosols during a month of serious pollution in Beijing, 2013

2014 ◽  
Vol 14 (6) ◽  
pp. 2887-2903 ◽  
Author(s):  
J. K. Zhang ◽  
Y. Sun ◽  
Z. R. Liu ◽  
D. S. Ji ◽  
B. Hu ◽  
...  
Keyword(s):  
Mass Concentration ◽  
Detailed Comparison ◽  
Organic Aerosol ◽  
Submicron Particles ◽  
Urban Site ◽  
Air Masses ◽  
Aerosol Mass ◽  
Inorganic Species ◽  
Mass Fractions ◽  
High Pollution

Abstract. In January 2013, Beijing experienced several serious haze events. To achieve a better understanding of the characteristics, sources and processes of aerosols during this month, an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at an urban site between 1 January and 1 February 2013 to obtain the size-resolved chemical composition of non-refractory submicron particles (NR-PM1). During this period, the mean measured NR-PM1 mass concentration was 89.3 ± 85.6 μg m−3, and it peaked at 423 μg m−3. Positive matrix factorization (PMF) differentiated the organic aerosol into five components, including a highly oxidized, low-volatility oxygenated organic aerosol (LV-OOA), a less oxidized, semi-volatile oxygenated OA (SV-OOA), a coal combustion OA (CCOA), a cooking-related OA (COA), and a hydrocarbon-like OA (HOA), which on average accounted for 28%, 26%, 15%, 20% and 11% of the total organic mass, respectively. A detailed comparison between the polluted days and unpolluted days found many interesting results. First, the organic fraction was the most important NR-PM1 species during the unpolluted days (58%), while inorganic species were dominant on polluted days (59%). The OA composition also experienced a significant change; it was dominated by primary OA (POA), including COA, HOA and CCOA, on unpolluted days. The contribution of secondary OA (SOA) increased from 35% to 63% between unpolluted and polluted days. Second, meteorological effects played an important role in the heavy pollution in this month and differed significantly between the two types of days. The temperature and relative humidity (RH) were all increased on polluted days and the wind speed and air pressure were decreased. Third, the diurnal variation trend in NR-PM1 species and OA components showed some differences between the two types of days, and the OA was more highly oxidized on polluted days. Fourth, the effects of air masses were significantly different between the two types of days; air was mainly transported from contaminated areas on the polluted days. The comparison also found that the aerosol was more acidic on polluted days. Additionally, the variation trends of the mass concentration and mass fractions of NR-PM1 species and OA components were more dramatic when the NR-PM1 mass loading was at a higher level. The serious pollution observed in this month can be attributed to the synergy of unfavorable meteorological factors, the transport of air masses from high-pollution areas, emission by local sources, and other factors.

scholarly journals Evaluation of the new capture vaporizer for Aerosol Mass Spectrometers (AMS) through laboratory studies of inorganic species

2016 ◽  
Author(s):  
Weiwei Hu ◽  
Pedro Campuzano-Jost ◽  
Douglas A. Day ◽  
Philip Croteau ◽  
Manjula R. Canagaratna ◽  
...  
Keyword(s):  
Collection Efficiency ◽  
Submicron Particles ◽  
Size Distributions ◽  
Laboratory Studies ◽  
Volatile Species ◽  
Pure Species ◽  
Mass Spectrometers ◽  
Aerosol Mass ◽  
Aerosol Mass Concentration ◽  
Inorganic Species

Abstract. Aerosol mass spectrometers (AMS) and Aerosol Chemical Speciation Monitors (ACSM) commercialized by Aerodyne Research Inc. are used widely to measure the mass concentrations and size distributions of non-refractory species in submicron-particles. With the "standard" vaporizer (SV) that is installed in all commercial instruments to date, the quantification of ambient aerosol mass concentration requires the use of a collection efficiency (CE) for correcting the loss of particles due to bounce on the SV. However, CE depends on aerosol phase, and thus can vary with location, airmass, and season of sampling. Although a composition-dependent parameterization of CE in the SV for ambient data has been successful, CE still contributes most of the estimated uncertainty to reported concentrations, and is also an important uncertainty in laboratory studies. To address this limitation, a new "capture" vaporizer (CV) has been designed to reduce or eliminate particle bounce and thus the need for a CE correction. To test the performance of the CV, two high-resolution AMS instruments, one with a SV and one with a CV were operated side by side in the laboratory. Four standard species NH4NO3, NaNO3, (NH4)2SO4 and NH4Cl, which typically constitute the majority of the mass of ambient submicron inorganic species, are studied. The effect of vaporizer temperature (Tv ~ 200–800 ℃) on the detected fragments, CE and size distributions are investigated. A Tv of 500–550 ℃ for the CV is recommended based on the observed performance. In the CV, CE was identical (around unity) for more volatile species and comparable or higher compared to the SV for less volatile species, demonstrating a substantial improvement in CE of inorganic species in the CV. The detected fragments of NO3 and SO4 species observed with the CV are different than those observed with the SV, suggesting additional thermal decomposition arising from the increased residence time and hot surface collisions. Longer particle detection times lead to broadened particle size distribution measurements made with the AMS. The degradation of CV size distributions due to this broadening is significant for laboratory studies using monodisperse particles, but minor for field studies since ambient distributions are typically quite broad. A method for estimating whether pure species will be detected in AMS sizing mode is proposed. Production of CO2(g) from sampled nitrate on the vaporizer surface, which has been reported for the SV, is negligible for the CV for NH4NO3 and comparable to the SV for NaNO3. Adjusting the alignment of aerodynamic lens to focus particles on the edge of the CV results in higher resolution size distributions, which can be useful in some laboratory experiments. We observe an extremely consistent detection of ammonium from different inorganic ammonium salts, independent of the vaporizer types and/or the Tv. This contradicts a recent suggestion by Murphy (2016) that inorganic species evaporate as intact salts in the AMS.

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