Relating hygroscopicity and composition of organic aerosol particulate matter

A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "κorg" parameter, and f44 was determined and is given by κorg=2.2×f44−0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass

Relating hygroscopicity and composition of organic aerosol particulate matter

A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "ϰorg" parameter, and f44 was determined and is given by ϰorg = 2.2 × f44 − 0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass

On the Influence of VOCs on New Particle Growth in a Continental-Mediterranean Region

[Abstract] A field campaign has been performed in the Madrid region to study the VOC influence in the growth of new particles in ambient air. A number of instruments have been deployed to characterize the main pollutant gases and particle properties and composition. The measurements were performed simultaneously at three sites (rural, urban background and urban traffic influenced) in the period 1–17 July 2019. The sites: Tres Cantos (rural), CIEMAT (urban background) and Leganés (urban traffic) were located within the Madrid airshed. Particle size distributions, mass concentrations at fractions PM10, PM2.5 and PM1, black carbon, VOCs species and gaseous pollutants (NOx and O3) were obtained in the sites. Some supplementary measurements were obtained in at least one of the sites: meteorological parameters, non-refractory submicron aerosol species and vertical profiles of aerosol optical properties. It has been observed that the new particle formation (NPF) events, nucleation and subsequent growth, happened at a regional scale, although differently among the sites. In the rural site, fewer events than expected were observed because of the high temperatures that affected the BVOC emissions. In the urban background site, the highest number of events was reached. In this station, it is common to receive air masses from the nearby forest and from the urban area, producing a mix of conditions with high BVOC and AVOC concentrations. In the urban traffic site, several NPF cases appeared, being a site dominated by AVOCs. Among the BVOCs measured in the three stations, the most common were α-Pinene and Limonene. Among the AVOCs measured, aromatics and linear hydrocarbon compounds for C10 and above were found. The linear group was found to be predominant during the NPF event days in the urban background site. This work provides new insights about the aerosol-forming precursors and growth of new particles in the Madrid region.This research has been partially funded by the CRISOL Project (CGL2017-85344-R MINECO/AEI/FEDER, UE), OASIS project (PID2021-127885OB-I00 fund by MCIN/ AEI/10.13039/501100011033 and by 'ERDF A way of making Europe') and by the TIGAS-CM project (Madrid Regional Government Y2018/EMT-5177)Comunidad de Madrid; Y2018/EMT-517

Solutions for the size & concentration measurement of aerosols from combustion

Currently the main pollution comes from the anthropogenic sources related to residential heating and combustion. Most of the emitted particles from this sources are in the mode below 1 μm. Therefore, only by using methods based on the electric mobility separation and size enhancement we can measure the size and concentration of this particles from nano to ultrafine sizes. This contribution describes the most recent methods how to study particle size and concentration of the particles coming from combustion sources

Solutions for the size & concentration measurement of aerosols from combustion

Currently the main pollution comes from the anthropogenic sources related to residential heating and combustion. Most of the emitted particles from this sources are in the mode below 1 μm. Therefore, only by using methods based on the electric mobility separation and size enhancement we can measure the size and concentration of this particles from nano to ultrafine sizes. This contribution describes the most recent methods how to study particle size and concentration of the particles coming from combustion sources

Extending traceability in airborne particle size distribution measurements beyond 10 µm : Counting efficiency and unit-to-unit variability of four aerodynamic particle size spectrometers

The aim of this study was to establish traceable number concentration measurements of airborne particles beyond 10 μm in particle size. To this end, the primary standards for particle number concentration at the National Metrology Institutes of Switzerland and Japan were further developed to extend their measurement capabilities. Details on the upgraded setup are provided. An inter-comparison of the two primary standards using an optical particle counter as transfer standard showed that these agree well within the stated uncertainties at polystyrene (PS) equivalent optical diameter of 15 µm. Subsequently, four Model 3321 (TSI Inc., USA) aerodynamic particle size spectrometers (APS) were calibrated against the primary standard of Switzerland using size-certified PS spheres with optical/aerodynamic diameter up to 20 µm as test aerosols. The counting efficiency profile and unit-to-unit variability of the APS units were determined. The results presented here can be useful for the analysis and interpretation of data collected by the different atmospheric aerosol networks worldwide. The outlined methodology can also be applied in the calibration of automated bio-aerosol monitors

Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles

A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, −30 °C, −35 °C and −40 °C. Freshly emitted diesel particles showed ice formation only at −40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where α-pinene was added for the ageing process, showed an ice nucleation enhancement at −35 °C. Wood burning particles also act as ice nuclei (IN) at −40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at −35 °C whereas no ice nucleation was observed at −30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below −40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.ISSN:1680-7375ISSN:1680-736