Air quality changes in cities during the COVID-19 lockdown: A critical review.

As part of a large study investigating indoor air in residential houses in Brisbane, Australia, the purpose of this work
was to quantify emission characteristics of indoor particle sources in 15 houses. Submicrometer particle number and
approximation of PM2.5 concentrations were measured simultaneously for more than 48 h in the kitchen of all the
houses by usinga condensation particle counter (CPC) and a photometer (DustTrak), respectively. In addition,
characterizations of particles resultingfrom cookingconducted in an identical way in all the houses were measured by
usinga scanningmobility particle sizer (SMPS), an aerodynamic particle sizer (APS) and a DustTrak. All the events of
elevated particle concentrations were linked to indoor activities usinghouse occupants diary entries, and catalogued
into 21 different types of indoor activities. This enabled quantification of the effect of indoor sources on indoor particle
concentrations as well as quantification of emission rates from the sources. For example, the study found that frying,
grilling, stove use, toasting, cooking pizza, cooking, candle vaporizing eucalyptus oil and fan heater use, could elevate
the indoor submicrometer particle number concentration levels by more than five times, while PM2.5 concentrations
could be up to 3, 30 and 90 times higher than the background levels during smoking, frying and grilling, respectively.
r 2004 Elsevier Ltd. All rights reserved.

Contribution from indoor sources to particle number and mass concentrations in residential houses

This work describes a methodology for the definition of indoor air quality monitoring plans in schools and above all to improve the knowledge and evaluation of the indoor concentration levels of some chemical pollutants. The aim is to guide interventions to improve the health of students and exposed staff connected with the activities carried out there. The proposed methodology is based on the simultaneous study of chemical (indoor/outdoor PM2.5, NO2, CO2) and physical (temperature, humidity) parameters by means of automatic analyzers coupled with gaseous compounds (benzene, toluene, ethylbenzene, xylenes, formaldehyde and NO2) sampled by denuders. The important novelty is that all the data were collected daily in two different situations, i.e., during school activities and no-school activities, allowing us to evaluate the exposure of each student or person. The different behaviors of all the measured pollutants during the two different situations are reported and commented on. Finally, a statistical approach will show how the investigated compounds are distributed around the two components of combustion processes and photochemical reactions.

https://www.mdpi.com/1660-4601/17/18/6695/pdf

Indoor Air Quality Levels in Schools: Role of Student Activities and No Activities.

The aim of this work was to investigate ultrafine particles (< 0.1 μm) in primary school classrooms, in relation to the classrooms activities. The investigations were conducted in three classrooms during two measuring campaigns, which together encompassed a period of 60 days. Initial investigations showed that under the normal operating conditions of the school there were many occasions in all three classrooms where indoor particle concentrations increased significantly compared to outdoor levels. By far the highest increases in the classroom resulted from art activities (painting, gluing and drawing), at times reaching over 1.4 x 105 particle cm-3. The indoor particle concentrations exceeded outdoor concentrations by approximately one order of magnitude, with a count median diameter ranging from 20-50 nm. Significant increases also occurred during cleaning activities, when detergents were used. GC-MS analysis conducted on 4 samples randomly selected from about 30 different paints and glues, as well as the detergent used in the school, showed that d-limonene was one of the main organic compounds of the detergent, however, it was not detected in the samples of the paints and the glue. Controlled experiments showed that this monoterpene, emitted from the detergent, reacted with O3 (at outdoor ambient concentrations ranging from 0.06-0.08ppm) and formed secondary organic aerosols. Further investigations to identify other liquids which may be potential sources of the precursors of secondary organic aerosols, were outside the scope of this project, however, it is expected that the problem identified by this study could be more widely spread, since most primary schools use liquid materials for art classes, and all schools use detergents for cleaning. Further studies are therefore recommended to better understand this phenomenon and also to minimize school children exposure to ultrafine particles from these indoor sources.

Ultrafine particles in indoor air of a school : possible role of secondary organic aerosols

Ventilation in built environments is essential to guarantee a good indoor air quality and a reduced probability of infection related to virus transmission Measuring ventilation-related parameters is not easy and currently two methods can be adopted: pressurization and tracer gas decay The pressurization test measures the airtightness of the building, whereas the tracer gas decay test measures the actual (site- and climate-specific) air exchange rate Finding a relationship amongst the results provided by the two tests would be very useful in view of an exhaustive characterization of the building ventilation, but it still remains an open challenge for the scientific literature The present paper aims at investigating the criticalities in correlating the two methods; thus, an experimental campaign was performed in a multi-room dwelling performing both air permeability and air exchange rate measurements in the entire dwelling and in parts of it A detailed uncertainty budget of the two methods was also carried out in order to perform metrological compatibility analyses The results of the campaign highlighted that the actual air exchange rates of the dwelling present a huge variability (from 100, with an exponential decrease as the wind velocity increases Thus, adopting constant conversion factors could significantly overestimate the actual ventilation of the building

Natural ventilation measurements in a multi-room dwelling: Critical aspects and comparability of pressurization and tracer gas decay tests

The new particle formation due to the use of cleaning products containing volatile organic compounds (VOCs) in indoor environments is well documented in the scientific literature. Indeed, the physical-chemical process occurring in particle nucleation due to VOC-ozone reactions was deepened as well as the effect of the main influencing parameters (ie, temperature, ozone). Nonetheless, proper quantification of the emission under actual meteo-climatic conditions and ozone concentrations is not available. To this end, in the present paper the emission factors of newly generated ultrafine particles due to the use of different floor cleaning products under actual temperature and relative humidity conditions and ozone concentrations typical of the summer periods were evaluated. Tests in a chamber and in an actual indoor environment were performed measuring continuously particle number concentrations and size distributions during cleaning activities. The tests revealed that a significant particle emission in the nucleation mode was present for half of the products under investigation with emission factors up to 1.1 × 1011 part./m2 (8.8 × 1010 part./mLproduct ), then leading to an overall particle emission comparable to other well-known indoor sources when cleaning wide surfaces.

/pdf/ultrafine-particle-emission-from-floor-cleaning-products-vc890460qn.pdf

Gianmarco De Luca

Papers

Ultrafine particle emission from floor cleaning products.