ORCID Profile
0000-0002-7097-1430
Current Organisation
Princeton University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Copernicus GmbH
Date: 15-06-2023
Abstract: Abstract. Currently, the complete chemical characterization of nanoparticles ( 100 nm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization have been recently developed to better detect and infer more accurately the sources and fates of sub-100 nm particles, but a detailed comparison of different approaches is missing. Here we report on the chemical composition of secondary organic aerosol (SOA) nanoparticles from experimental studies of α-pinene ozonolysis at −50, −30, and −10 ∘C and intercompare the results measured by different techniques. The experiments were performed at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). The chemical composition was measured simultaneously by four different techniques: (1) thermal desorption–differential mobility analyzer (TD–DMA) coupled to a NO3- chemical ionization–atmospheric-pressure-interface–time-of-flight (CI–APi–TOF) mass spectrometer, (2) filter inlet for gases and aerosols (FIGAERO) coupled to an I− high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS), (3) extractive electrospray Na+ ionization time-of-flight mass spectrometer (EESI-TOF), and (4) offline analysis of filters (FILTER) using ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS). Intercomparison was performed by contrasting the observed chemical composition as a function of oxidation state and carbon number, by estimating the volatility and comparing the fraction of volatility classes, and by comparing the thermal desorption behavior (for the thermal desorption techniques: TD–DMA and FIGAERO) and performing positive matrix factorization (PMF) analysis for the thermograms. We found that the methods generally agree on the most important compounds that are found in the nanoparticles. However, they do see different parts of the organic spectrum. We suggest potential explanations for these differences: thermal decomposition, aging, s ling artifacts, etc. We applied PMF analysis and found insights of thermal decomposition in the TD–DMA and the FIGAERO.
Publisher: Copernicus GmbH
Date: 07-07-2021
DOI: 10.5194/ACP-2021-512
Abstract: Abstract. New Particle Formation (NPF) from biogenic organic precursors is an important atmospheric process. One of the major species is α-pinene, which upon oxidation, can form a suite of products covering a wide range of volatilities. A fraction of the oxidation products is termed Highly Oxygenated Organic Molecules (HOM). These play a crucial role for nucleation and the formation of Secondary Organic Aerosol (SOA). However, measuring the composition of newly formed particles is challenging due to their very small mass. Here, we present results on the gas and particle phase chemical composition for a system where α-pinene was oxidized by ozone, and for a mixed system of α-pinene and isoprene, respectively. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber at temperatures between −50 °C and −30 °C and at low and high relative humidity (20 % and 60 to 100 % RH). These conditions were chosen to simulate pure biogenic new particle formation in the upper free troposphere. The particle chemical composition was analyzed by the Thermal Desorption-Differential Mobility Analyzer (TD-DMA) coupled to a nitrate chemical ionization time-of-flight mass spectrometer. This instrument can be used for particle and gas phase measurements using the same ionization and detection scheme. Our measurements revealed the presence of C8-10 monomers and C18-20 dimers as the major compounds in the particles (diameter up to ~ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5-7) and C15 compounds (C15H24O5-10) are detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene might enhance growth at particle sizes larger than 15 nm. Besides the chemical information regarding the HOM formation for the α-pinene (plus isoprene) system, we report on the nucleation rates measured at 1.7 nm and found that the lower J1.7nm values compared with previous studies are very likely due to the higher α-pinene and ozone mixing ratios used in the present study
Publisher: Springer Science and Business Media LLC
Date: 18-05-2022
DOI: 10.1038/S41586-022-04605-4
Abstract: New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN) 1–4 . However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region 5,6 . Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO 3 –H 2 SO 4 –NH 3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.
Publisher: Research Square Platform LLC
Date: 05-04-2023
DOI: 10.21203/RS.3.RS-2722087/V1
Abstract: Highly oxygenated organic molecules (HOMs) are a major source of new particles affecting Earth’s climate 1,2 . HOM production from the oxidation of volatile organic compounds (VOCs) occurs during both day and night, and can lead to new particle formation (NPF) 3,4 . However, NPF involving organic vapors has been reported much more often during daytime 3-6 than during nighttime 7,8 . Here, we show that the nitrate radicals (NO 3 ) - which arise predominantly at night – inhibit NPF during the oxidation of monoterpenes based on three lines of observational evidence: NPF experiments in the CLOUD chamber at CERN radical chemistry experiments using an oxidation flow reactor and field observations in a wetland that occasionally exhibits nocturnal NPF. Nitrooxy-peroxy radicals formed from NO 3 chemistry suppress the production of ultra-low volatility organic compounds (ULVOCs) responsible for biogenic NPF, which are covalently bound RO 2 dimer association products. The ULVOC yield of α-pinene in the presence of NO3 is one-fifth of that resulting from ozone chemistry alone. Even trace amounts of NO 3 radicals, at sub parts per trillion level, suppress the NPF rate by a factor of 4. Ambient observations further confirm that when NO 3 chemistry is involved, monoterpene NPF is completely turned off. Our results explain the frequent absence of nocturnal biogenic NPF in monoterpene-rich environments.
Publisher: Copernicus GmbH
Date: 26-08-2022
DOI: 10.5194/ACP-2022-498
Abstract: Abstract. Currently, the complete chemical characterization of nanoparticles ( nm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization have been recently developed to better detect and infer more accurately the sources and fates of ultra-fine particles, but a detailed comparison of different approaches is missing. Here we report on the chemical composition of secondary organic aerosol (SOA) nanoparticles from experimental studies of α-pinene ozonolysis at -50 ºC, -30 ºC, and -10 ºC, and inter-compare the results measured by different techniques. The experiments were performed at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). The chemical composition was measured simultaneously by four different techniques: 1) Thermal Desorption-Differential Mobility Analyzer (TD-DMA) coupled to a NO3- chemical ionization-atmospheric-pressure-interface-time-of-flight (CI-APi-TOF) mass spectrometer, 2) Filter Inlet for Gases and AEROsols (FIGAERO) coupled to an I- high-resolution time-of-flight chemical-ionization mass spectrometer (HRToF-CIMS), 3) Extractive Electrospray Na+ Ionization time-of-flight mass spectrometer (EESI-TOF), and 4) Offline analysis of filters (FILTER) using Ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS). Intercomparison was performed by contrasting the observed chemical composition as a function of oxidation state and carbon number, by calculating the volatility and comparing the fraction of volatility classes, and by comparing the thermal desorption behavior (for the thermal desorption techniques: TD-DMA and FIGAERO) and performing positive matrix factorization (PMF) analysis for the thermograms. We found that the methods generally agree on the most important compounds that are found in the nanoparticles. However, they do see different parts of the organic spectrum. We suggest potential explanations for these differences: thermal decomposition, aging, s ling artifacts, etc. We applied PMF analysis and found insights of thermal decomposition in the TD-DMA and the FIGAERO.
Publisher: Copernicus GmbH
Date: 26-08-2022
Publisher: Copernicus GmbH
Date: 25-11-2021
DOI: 10.5194/ACP-21-17099-2021
Abstract: Abstract. Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Publisher: Copernicus GmbH
Date: 07-07-2021
No related grants have been discovered for Naser Mahfouz.