Experimental study on the influence of dimethylamine on the detection of gas phase sulfuric acid using chemical ionization mass spectrometry (CIMS)

Based on quantum chemistry calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H_2SO_4) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment was set up at the CLOUD aerosol chamber to test the quantitative detection of H_2SO_4 by CIMS by directly comparing the measured H_2SO_4 with and without DMA being present in the sample air. It was found that the H_2SO_4 cluster distribution changes but the CIMS detection efficiency is not strongly influenced

A double inversion: Size and time resolved growth rates for aerosol particles in the CERN CLOUD experiment

An integrated analysis of multiple instruments measuring concentrations of aerosol particles in the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN obtains size and time dependent growth rates. A matrix inversion is performed twice: first to get size distributions from measured concentrations using instrument transfer functions; secondly to get growth rates from size distributions using the aerosol general dynamic equation (GDE)

Nitrate Radicals Suppress Biogenic New Particle Formation from Monoterpene Oxidation

Highly oxygenated organic molecules (HOMs) are a major source of new particles that affect the Earth’s climate. HOM production from the oxidation of volatile organic compounds (VOCs) occurs during both the day and night and can lead to new particle formation (NPF). However, NPF involving organic vapors has been reported much more often during the daytime than during nighttime. Here, we show that the nitrate radicals (NO3), which arise predominantly at night, inhibit NPF during the oxidation of monoterpenes based on three lines of observational evidence: NPF experiments in the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN (European Organization for Nuclear Research), radical chemistry experiments using an oxidation flow reactor, and field observations in a wetland that occasionally exhibits nocturnal NPF. Nitrooxy-peroxy radicals formed from NO3 chemistry suppress the production of ultralow-volatility organic compounds (ULVOCs) responsible for biogenic NPF, which are covalently bound peroxy radical (RO2) 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 NO3 radicals, at sub-parts per trillion level, suppress the NPF rate by a factor of 4. Ambient observations further confirm that when NO3 chemistry is involved, monoterpene NPF is completely turned off. Our results explain the frequent absence of nocturnal biogenic NPF in monoterpene (α-pinene)-rich environments