Model Calculations of Aerosol Transmission and Infection Risk of COVID-19 in Indoor Environments.

The role of aerosolized SARS-CoV-2 viruses in airborne transmission of COVID-19 has been debated. The aerosols are transmitted through breathing and vocalization by infectious subjects. Some authors state that this represents the dominant route of spreading, while others dismiss the option. Here we present an adjustable algorithm to estimate the infection risk for different indoor environments, constrained by published data of human aerosol emissions, SARS-CoV-2 viral loads, infective dose and other parameters. We evaluate typical indoor settings such as an office, a classroom, choir practice, and a reception/party. Our results suggest that aerosols from highly infective subjects can effectively transmit COVID-19 in indoor environments. This "highly infective" category represents approximately 20% of the patients who tested positive for SARS-CoV-2. We find that "super infective" subjects, representing the top 5-10% of subjects with a positive test, plus an unknown fraction of less-but still highly infective, high aerosol-emitting subjects-may cause COVID-19 clusters (>10 infections). In general, active room ventilation and the ubiquitous wearing of face masks (i.e., by all subjects) may reduce the individual infection risk by a factor of five to ten, similar to high-volume, high-efficiency particulate air (HEPA) filtering. A particularly effective mitigation measure is the use of high-quality masks, which can drastically reduce the indoor infection risk through aerosols.

Enhanced role of transition metal ion catalysis during in-cloud oxidation of SO2.

Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway-which is currently included in only one of the 12 major global climate models-will have a significant impact on assessments of current and future climate.

Effective broadband refractive index retrieval by a white light optical particle counter.

A new approach to retrieve the effective broadband refractive indices (nbroad,eff) of aerosol particles by a white light aerosol spectrometer (WELAS) optical particle counter (OPC) is presented. Using a tandem differential mobility analyzer (DMA)-OPC system, the nbroad,eff are obtained for both laboratory and field applications. This method was tested in the laboratory using substances with a wide range of optical properties. With the obtained nbroad,eff, WELAS aerosol size distributions can be corrected. Therefore, this method can be used for instrument calibration in both laboratory and field measurements. The retrieved effective broadband refractive indices for the scattering aerosols were: ammonium sulfate ((NH4)2SO4, AS) nbroad,eff=1.52(+/-0.01)+i0.0, glutaric acid (HOOC(CH2)3COOH, GA) nbroad,eff=1.45(+/-0.01)+i0.0, and sodium chloride (NaCl) nbroad,eff=1.49(+/-0.02)+i0.0, all within 4% of literature values. A lightly absorbing substance, Suwannee river fulvic acid (SRFA), was also measured, and its retrieved nbroad,eff is like that of a pure scatterer, with a value of nbroad,eff=1.53(+/-0.01)+i0.0. The retrieved real part of nbroad,eff is in accordance with literature values and the imaginary part with the behavior of the white light spectrum of the WELAS, which is not sensitive below a wavelength of 380 nm, where SRFA mainly absorbs. For absorbing substances, nigrosine and various mixtures of nigrosine with AS and GA were measured. For nigrosine, nbroad,eff=1.64(+/-0.04)+i0.20(+/-0.03) was retrieved, in very good agreement with values found in the literature. The nbroad,eff retrieved by this method for the mixtures was in accordance with the complex refractive index expected. The nbroad,eff retrieved by this method would be similar to the values obtained using the solar spectrum.

Trace detection of organic compounds in complex sample matrixes by single photon ionization ion trap mass spectrometry: real-time detection of security-relevant compounds and online analysis of the coffee-roasting process.

An in-house-built ion trap mass spectrometer combined with a soft ionization source has been set up and tested. As ionization source, an electron beam pumped vacuum UV (VUV) excimer lamp (EBEL) was used for single-photon ionization. It was shown that soft ionization allows the reduction of fragmentation of the target analytes and the suppression of most matrix components. Therefore, the combination of photon ionization with the tandem mass spectrometry (MS/MS) capability of an ion trap yields a powerful tool for molecular ion peak detection and identification of organic trace compounds in complex matrixes. This setup was successfully tested for two different applications. The first one is the detection of security-relevant substances like explosives, narcotics, and chemical warfare agents. One test substance from each of these groups was chosen and detected successfully with single photon ionization ion trap mass spectrometry (SPI-ITMS) MS/MS measurements. Additionally, first tests were performed, demonstrating that this method is not influenced by matrix compounds. The second field of application is the detection of process gases. Here, exhaust gas from coffee roasting was analyzed in real time, and some of its compounds were identified using MS/MS studies.