scholarly journals Modeling microbial growth in carpet dust exposed to diurnal variations in relative humidity using the “Time‐of‐Wetness” framework

Indoor Air ◽  
2020 ◽  
Vol 30 (5) ◽  
pp. 978-992 ◽  
Author(s):  
Sarah R. Haines ◽  
Jeffrey A. Siegel ◽  
Karen C. Dannemiller
Keyword(s):  
Relative Humidity ◽  
Microbial Growth ◽  
Diurnal Variations ◽  
Time Of Wetness

Toward more realistic time of wetness measurement by means of surface relative humidity

2020 ◽  
Vol 177 ◽  
pp. 108999 ◽  
Author(s):  
Mehrdad Hoseinpoor ◽  
Tomáš Prošek ◽  
Ludovic Babusiaux ◽  
Jacky Mallégol
Keyword(s):  
Relative Humidity ◽  
Time Of Wetness

Desiccation and storage of Panagrolaimus sp. (strain NFS-24-5)

Nematology ◽  
2013 ◽  
Vol 15 (5) ◽  
pp. 557-566 ◽  
Author(s):  
Hilke Honnens ◽  
Thomas Assheuer ◽  
Ralf-Udo Ehlers
Keyword(s):  
Relative Humidity ◽  
Size Distribution ◽  
Microbial Growth ◽  
Time Span ◽  
Small Scale ◽  
Nematode Density ◽  
Marine Aquaculture ◽  
Crustacean Species ◽  
Feeding Experiments ◽  
And Storage

Panagrolaimus sp. strain NFS-24-5 has potential to be used as live food for early stages of fish and crustacean species in marine aquaculture. One constraint to its commercialisation is the lack of a method that enables storage of nematodes over a longer time span. The objective of this study was to develop a procedure to transfer nematodes into a dormant state by desiccation. The nematodes were concentrated at densities of 25, 50, 100 and 200 × 103 individials cm−2 on nylon net or cellulose paper, preconditioned for 72 h at 97.3% relative humidity (RH) and then stored at 52.9 or 32.8% RH for 1 week. Cellulose was a better carrier for the nematodes. Survival of the nematodes was reduced only at the highest nematode density on both materials. The water activity of desiccated nematodes was 0.44 and 0.33 at 52.9% and 32.8% RH, respectively, well beyond a point to prevent microbial growth. After storage over a period of 10 weeks at 25 × 103 nematodes cm−2 at 52.9 and 32.8% RH, 92% of the nematodes were still alive. Monitoring the size distribution revealed no changes at 52.9% RH, but there were more of the larger nematodes dying at 32.8% RH in two out of three experiments. The method can be used to store quiescent Panagrolaimus sp. (strain NFS-24-5) for transportation and use in small scale feeding experiments for marine fish and crustacean larvae.

scholarly journals Factors Influencing the Development of Microbes in Food

2020 ◽  
Vol 7 (3) ◽  
pp. 57-77
Author(s):  
S S Preetha ◽  
Rita Narayanan
Keyword(s):  
Relative Humidity ◽  
Food Environment ◽  
Microbial Growth ◽  
Storage Temperature ◽  
Nutrient Content ◽  
Review Article ◽  
Intrinsic Factors ◽  
Gaseous Environment ◽  
Factors Influencing ◽  
Extrinsic Parameters

In this review article, the different parameters, mostly intrinsic, extrinsic, implicit, and processing, that have an impact on the microbial growth in the food environment has been discussed in detail. Intrinsic factors (pH, moisture content, O/R potential, antimicrobial constituents, biological structures, and nutrient content) as well as extrinsic parameters (Relative humidity, storage temperature, gaseous environment and activities of other microbes in the environment) determines the range and population of microorganisms associated with the food at any given point throughout their production and post-harvest handling, thus influencing the rate and type of spoilage that eventually renders the food inedible.

Risk for Mould Growth on Hemp-Lime at Different Relative Humidity

2022 ◽  
Author(s):  
Sanne Johansson ◽  
Kristin Balksten ◽  
Paulien Brigitte Strandberg-de Bruijn
Keyword(s):  
Relative Humidity ◽  
Building Materials ◽  
Microbial Growth ◽  
Mould Growth ◽  
European Climate ◽  
Northern European ◽  
Critical Relative Humidity ◽  
Different Temperatures ◽  
Critical Moisture ◽  
Hemp Shiv

Microbial growth often thrives in humid conditions, at high relative humidity. Moulds are complex organisms; many types of mould are able to survive strong variations in humidity and temperature, such as those on building façades. For some building materials a critical relative humidity is determined, which functions as a theoretical threshold; at this (or lower) relative humidity microbial growth will likely not occur. Hemp-lime is a building material that consists of hemp shiv (the woody core parts of the hemp stem) and building lime. It is a material that can be used for walls, and even though it has been used for more than 20 years, thusfar little is known about its critical moisture levels for microbial growth. The aim of this research was therefore to determine at what relative humidity microbial growth occurs on carbonated hemp-lime material, and to study if there is a protective influence of a carbonated lime binder on the hemp shiv. The objective was to study microbial growth on hemp shiv, hemp-lime and on hemp with a thin layer of lime at three relative humidity (75 %, 85 % and 95 %) and at two different temperatures (15°C and 23°C); conditions that could occur naturally in a hemp-lime façade exposed to high rain loads in a northern European climate. Hemp shiv seems to have a relatively low resistance to microbial growth, similar to that of wood. However, because the hemp is protected by lime it can withstand much higher relative humidity without microbial growth occurring on the material. The critical moisture level for hemp-lime seemed to occur between 75 and 85 % RH, while the material was completely without microbial growth at 75 % RH. The lime had a protective effect on the hemp and acted as a mould inhibitor, both over time and with varying temperature and humidity.

Forecasting diurnal variations in meteorological parameters for predicting fire behaviour

1989 ◽  
Vol 19 (6) ◽  
pp. 791-797 ◽  
Author(s):  
J. A. Beck ◽  
A. C. F. Trevitt
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Absolute Humidity ◽  
Diurnal Variations ◽  
Day Length ◽  
Maximum Temperature ◽  
Daily Maximum ◽  
Fire Behaviour ◽  
Julian Date ◽  
Time Of Year

Empirical models for predicting diurnal variations in air temperature, wind speed, and relative humidity, given daily maximum and minimum values, latitude, and Julian date, have been developed. Solar heating during the daytime is quantitatively depicted using a truncated sine function, and nighttime cooling is characterized by an exponential decay function. Daily wind-speed trends echo diurnal temperature patterns, and relative humidity is modelled as a function of temperature by assuming that absolute humidity remains constant throughout the day. The time of occurrence of daily maxima and minima in temperature and wind speed varies seasonally according to changes in day length. Maximum temperature and wind speed typically occur later in the day than the maximum solar insolation. The magnitude of this lag depends on both time of year and latitude. The models were parameterized for two locations in Australia and observed, and modelled variations in temperature, relative humidity, and wind speed were used to forecast diurnal trends in fire behaviour. Predicted fire behaviour compared favourably in the two cases considering the very simple modelling approach employed.

scholarly journals Hygroscopic properties of aerosol particles at high relative humidity and their diurnal variations in the North China Plain

2011 ◽  
Vol 11 (7) ◽  
pp. 3479-3494 ◽  
Author(s):  
P. F. Liu ◽  
C. S. Zhao ◽  
T. Göbel ◽  
E. Hallbauer ◽  
A. Nowak ◽  
...  
Keyword(s):  
Relative Humidity ◽  
North China Plain ◽  
North China ◽  
Aerosol Particles ◽  
Diurnal Variations ◽  
Hygroscopic Growth ◽  
Carbonaceous Particles ◽  
The North ◽  
Hygroscopic Properties ◽  
The North China Plain

Abstract. The hygroscopic properties of submicron aerosol particles were determined at a suburban site (Wuqing) in the North China Plain among a cluster of cities during the period 17 July to 12 August, 2009. A High Humidity Tandem Differential Mobility Analyser (HH-TDMA) instrument was applied to measure the hygroscopic growth factor (GF) at 90%, 95% and 98.5% relative humidity (RH) for particles with dry diameters between 50 and 250 nm. The probability distribution of GF (GF-PDF) averaged over the period shows a distinct bimodal pattern, namely, a dominant more-hygroscopic (MH) group and a smaller nearly-hydrophobic (NH) group. The MH group particles were highly hygroscopic, and their GF was relatively constant during the period with average values of 1.54 ± 0.02, 1.81 ± 0.04 and 2.45 ± 0.07 at 90%, 95% and 98.5% RH (D0 = 100 nm), respectively. The NH group particles grew very slightly when exposed to high RH, with GF values of 1.08 ± 0.02, 1.13 ± 0.06 and 1.24 ± 0.13 respectively at 90%, 95% and 98.5% RH (D0 = 100 nm). The hygroscopic growth behaviours at different RHs were well represented by a single-parameter Köhler model. Thus, the calculation of GF as a function of RH and dry diameter could be facilitated by an empirical parameterization of κ as function of dry diameter. A strong diurnal pattern in number fraction of different hygroscopic groups was observed. The average number fraction of NH particles during the day was about 8%, while during the nighttime fractions up to 20% were reached. Correspondingly, the state of mixing in terms of water uptake varied significantly during a day. Simulations using a particle-resolved aerosol box model (PartMC-MOSAIC) suggest that the diurnal variations of aerosol hygroscopicity and mixing state were mainly caused by the evolution of the atmospheric mixing layer. The shallow nocturnal boundary layer during the night facilitated the accumulation of freshly emitted carbonaceous particles (mainly hydrophobic) near the surface while in the morning turbulence entrained the more aged and more hygroscopic particles from aloft and diluted the NH particles near the surface resulting in a decrease in the fraction of NH particles.

scholarly journals Microbial growth and volatile organic compound (VOC) emissions from carpet and drywall under elevated relative humidity conditions

Microbiome ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Sarah R. Haines ◽  
Emma C. Hall ◽  
Katarzyna Marciniak ◽  
Pawel K. Misztal ◽  
Allen H. Goldstein ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Relative Humidity ◽  
Species Composition ◽  
Organic Compounds ◽  
Building Materials ◽  
Microbial Growth ◽  
Collection Site ◽  
Material Type ◽  
Microbial Species ◽  
Volatile Organic

Abstract Background Microbes can grow in indoor environments if moisture is available, and we need an improved understanding of how this growth contributes to emissions of microbial volatile organic compounds (mVOCs). The goal of this study was to measure how moisture levels, building material type, collection site, and microbial species composition impact microbial growth and emissions of mVOCs. We subjected two common building materials, drywall, and carpet, to treatments with varying moisture availability and measured microbial communities and mVOC emissions. Results Fungal growth occurred in samples at >75% equilibrium relative humidity (ERH) for carpet with dust and >85% ERH for inoculated painted drywall. In addition to incubated relative humidity level, dust sample collection site (adonis p=0.001) and material type (drywall, carpet, adonis p=0.001) drove fungal and bacterial species composition. Increased relative humidity was associated with decreased microbial species diversity in samples of carpet with dust (adonis p= 0.005). Abundant volatile organic compounds (VOCs) that accounted for >1% emissions were likely released from building materials and the dust itself. However, certain mVOCs were associated with microbial growth from carpet with dust such as C10H16H+ (monoterpenes) and C2H6SH+ (dimethyl sulfide and ethanethiol). CO2 production from samples of carpet with dust at 95% ERH averaged 5.92 mg hr-1 kg-1, while the average for carpet without dust at 95% ERH was 2.55 mg hr-1 kg-1. Conclusion Microbial growth and mVOC emissions occur at lower relative humidity in carpet and floor dust compared to drywall, which has important implications for human exposure. Even under elevated relative humidity conditions, the VOC emissions profile is dominated by non-microbial VOCs, although potential mVOCs may dominate odor production.

scholarly journals Diurnal variations of cloud and relative humidity profiles across the tropics

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
H. Chepfer ◽  
H. Brogniez ◽  
V. Noel
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Diurnal Variations ◽  
Lower Atmosphere ◽  
Positive Anomaly ◽  
Solar Forcing ◽  
Early Afternoon ◽  
Thin Cloud ◽  
The Tropics ◽  
Humidity Profiles

Abstract Even though the diurnal cycle of solar forcing on the climate system is well defined, the diurnal evolutions of water vapor and clouds induced by the solar forcing are not yet established across the tropics. Here we combine recent satellite observations of clouds profiles and relative humidity profiles to document the diurnal variations of the water vapor and clouds vertical distributions over all the tropics in June-July-August. While the daily mean water vapor and cloud profiles are different between land and ocean, their diurnal variations with respect to their daily means exhibit similar features. Relative humidity profiles and optically thin cloud fraction profiles vary together which maximize during night-time in the entire troposphere and a minimize in day-time. The fraction of optically opaque clouds peak in the free troposphere in the early afternoon, transforms into a high altitude positive anomaly of optically thin clouds from nightfall to sunrise. In addition, land regions exhibit a daily low thin cloud positive anomaly, while oceanic regions exposed to subsidence air motions exhibit positive anomalies of opaque clouds in the lower atmosphere during the second half of the night, which grow until sunrise.

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