Ventilation of indoor formaldehyde and estimation of its emission and air exchange rate

Residents living in the cold areas such as Harbin generally experience a residence time of approximately 6 months in chilly winter without frequent natural ventilation. To find out the influence of a short period of ventilation on the indoor formaldehyde concentration inside a new building, an investigation was conducted for the instance of twice ventilation in a day through window opening. The results showed that the initial concentration of formaldehyde was 3.53 -8. 48 times as high as the concentration after 10 min ventilation. After closing the window, the indoor formaldehyde concentration increased with time and followed an exponential equation of C = C0 exp（ - b ＊ t） ＋ （ a ＋ Cu, ） [ 1 - exp（ - b ＊ t） ] with correlation coefficient （ R^2 ） of 0. 945 - 0. 999, based on the statistical analysis of 14 groups of measurement data. The developed equation can be used to estimate the emission rate of indoor formaldehyde sources and the air exchange rate of the test room simultaneously.

Estimating the air exchange rates in naturally ventilated cattle houses using Bayesian-optimized GBDT

It is challenging to estimate the air exchange rate(AER)dynamically in naturally ventilated livestock buildings such as dairy houses due to the influence of complex and variable outdoor environmental factors,large opening ratios,and the confusion of inflow and outflow at openings.This makes it difficult to efficiently regulate the opening ratio to meet the ventilation requirements in naturally ventilated livestock buildings.In this study,the air exchange rates of naturally ventilated cattle houses(NVCHs)in different seasons and opening ratios were obtained through field measurements and computational fluid dynamics(CFD)simulations.A fast and efficient machine learning framework was proposed and examined to predict AER based on the gradient boosting decision tree(GBDT)combined with Bayesian optimization.Compared with commonly used machine learning models such as multilayer perceptrons(MLPs)and support vector machines(SVMs),the proposed GBDT model has higher prediction accuracy and can avoid falling easily into local optima.Compared with the existing mechanical model based on the Bernoulli equation,the proposed GBDT model showed a slightly higher prediction than the mechanistic model and was much easier to use in AER estimation when inputting easily collected environmental factors in practical applications.Using Bayesian optimization could dramatically reduce the computing time when determining the optimal hyperparameter for establishing the GBDT model,dramatically saving on computing resources.Based on the Bayesian optimized GBDT model,the desirable opening ratio of the side curtain can be determined for automatically regulating the AER of cattle houses in future applications.

Measurement of air exchange rates in different indoor environments using continuous CO_2 sensors

A new air exchange rate （AER） monitoring method using continuous CO2 sensors was developed and validated through both laboratory experiments and field studies. Controlled laboratory simulation tests were conducted in a 1-m3 environmental chamber at different AERs （0.1-10.0 hr-1）. AERs were determined using the decay method based on box model assumptions. Field tests were conducted in classrooms, dormitories, meeting rooms and apartments during 2-5 weekdays using CO2 sensors coupled with data loggers. Indoor temperature, relative humidity （RH）, and CO2 concentrations were continuously monitored while outdoor parameters combined with on-site climate conditions were recorded. Statistical results indicated that good laboratory performance was achieved： duplicate precision was within 10%, and the measured AERs were 90%-120% of the real AERs. Average AERs were 1.22, 1.37, 1.10, 1.91 and 0.73 hr-l in dormitories, air-conditioned classrooms, classrooms with an air circulation cooling system, reading rooms, and meeting rooms, respectively. In an elderly particulate matter exposure study, all the homes had AER values ranging from 0.29 to 3.46 hr-1 in fall, and 0.12 to 1.39 hr-1 in winter with a median AER of 1.15.

Vertical Air Mass Exchange Driven by the Local Circulation on the Northern Slope of Mount Everest

To better understand vertical air mass exchange driven by local circulation in the Himalayas, the volume flux of air mass is estimated in the Rongbuk Valley on the northern slope of Mount Everest, based on a volume closure method and wind-profiler measurements during the HEST2006 campaign in June 2006. Vertical air mass exchange was found to be dominated by a strong downward mass transfer from the late morning to late night. The average vertical air volume flux was 0.09 m s-1, which could be equivalent to a daily ventilation of 30 times the enclosed valley volume. This vertical air mass exchange process was greatly affected by the evolution of the South Asian summer monsoon （SASM）, with a strong downward transfer during the SASM break stage, and a weak transfer during the SASM active stage.

Quantitative Estimation of Air Mass Exchange by Along-Valley Wind in the Rongbuk Valley

For a better understanding of the air mass exchange processes between the surface and free atmos-phere in the Himalayas,a Himalayan exchange between the surface and troposphere 2007 (HEST2007) campaign was carried out in the Rongbuk Valley,on the northern slope of Mt.Qomolangma,in June 2007.The wind,tem-perature and radiation conditions were measured during the campaign.Using these observation data,together with the National Centers for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data,the air mass exchange between the inside of the valley and the outside of the valley is quantitatively estimated,based on a closed-valley method.The air mass is strongly injected into the Rongbuk Valley in the after-noon,which dominates the diurnal cycle,by a strong downward along-valley wind,with a maximum down-ward transfer rate of 9.4 cm s?1.The total air volume flux injected into the valley was 2.6×1011 m3 d?1 in 24 hours in June 2007,which is 15 times the total volume of the val-ley.The air mass transfer into the valley also exhibited a clear daily variation during the HEST2007 campaign,which can be affected by the synoptic situations through the adjustment of local radiation conditions.

Assessment of SARS-CoV-2 airborne infection transmission risk in public buses

Public transport environments are thought to play a key role in the spread of SARS-CoV-2 worldwide.Indeed,high crowding indexes(i.e.high numbers of people relative to the vehicle size),inadequate clean air supply,and frequent extended exposure durations make transport environments potential hotspots for transmission of respiratory infections.During the COVID-19 pandemic,generic mitigation measures(e.g.physical distancing)have been applied without also considering the airborne transmission route.This is due to the lack of quantified data about airborne contagion risk in transport environments.In this study,we apply a novel combination of close proximity and room-scale risk assessment approaches for people sharing public transport environments to predict their contagion risk due to SARS-CoV-2 respiratory infection.In particular,the individual infection risk of susceptible subjects and the transmissibility of SARS-CoV-2(expressed through the reproduction number)are evaluated for two types of buses,differing in terms of exposure time and crowding index:urban and long-distance buses.Infection risk and reproduction number are calculated for different scenarios as a function of the ventilation rates(both measured and estimated according to standards),crowding indexes,and travel times.The results show that for urban buses,the close proximity contribution significantly affects the maximum occupancy to maintain a reproductive number of<1.In particular,full occupancy of the bus would be permitted only for an infected subject breathing,whereas for an infected subject speaking,masking would be required.For long-distance buses,full occupancy of the bus can be maintained only if specific mitigation solutions are simultaneously applied.For example,for an infected person speaking for 1 h,appropriate filtration of the recirculated air and simultaneous use of FFP2 masks would permit full occupancy of the bus for a period of almost 8 h.Otherwise,a high percentage of immunized persons(>80%)would be needed.

An indoor air aerosol model for outdoor contaminant transmission into occupied rooms

The paper presents a simple model for outdoor air contaminant transmission into occupied rooms. In the model, several factors such as filtration, ventilation, deposition, re-emission, outdoor concentration and indoor sources are included. The model results show that the air exchange rate plays an important role in the transmission of outdoor contaminants into the indoor environment. The model shows that increasing the value of the filtration efficiency decreases the mass concentration of indoor particles. In addition, if outdoor aerosol particles have a periodic behaviour, indoor aerosol particles also behave periodically but smoother. Indoor sources are found to be able to increase indoor concentrations greatly and continuously.

Experimental study on the CO_(2) concentration and age of air distribution inside tiny sleeping spaces

In recent years,rapid urban development has led to capsule hotels,sleep pods,and other tiny sleeping spaces that adapt to people’s fast-paced lives,achieving maximum functionality with a very small footprint.However,due to the small space,human metabolic pollutant(such as CO_(2))is more likely to accumulate,and the air is not easily circulated.In this paper,a full-size experimental platform is set up with three types of ventilation modes to explore the exclusion efficiency of metabolic pollutants and the overall distribution of age of air under these ventilation modes.The conclusions showed that the mean values of metabolic pollutant exclusion rates for the different ventilation modalities varied very little across the spatial dimensions of the confined space but varied considerably in the area around the head.The double-side attached ventilation method was the most effective in removing human metabolic pollutants,especially in the head region(CN≥0.92),while the single-wall attached ventilation method had the best air exchange efficiency(η≥0.85).This suggests an inconsistent distribution of CO_(2) and age of air,which is contrary to general common sense.The conclusions of this paper can guide the design of ventilation for tiny sleeping spaces.

Study on the effect of Fresh Air Ventilation system for reducing indoor ^(222)Rn

Objective:To explore the reduction effect for the indoor ^(222)Rn(Rn)by Fresh Air Ventilation(FAV)system,a novel commercial ventilation device in China.Methods:The indoor concentrations of Rn and its decay products(RnD)in three residential rooms,two in Beijing and one in Hefei city,Anhui province,before and after FAVS functioned were measured using an active continuous method.The air exchange rate was monitored by measuring CO_(2) concentration using the tracer gas method.Results:In the three rooms,the FAVS reduced the Rn concentrations from(162±80)Bq/m^(3) to(63±22)Bq/m^(3) and decreased the RnD concentrations from(64±35)Bq/m^(3) to(13±6)Bq/m^(3) on average,a decrease of(59±25)% in the Rn concentrations and a drop of(77±18)%in the RnD concentrations.Considering dose conversion factors of Rn and RnD,FAVS decreased the exposure dose by(76±20)%.Besides,FAVS increased the air exchange rates from 0.17 h^(-1) to 0.56 h^(-1) on average.Conclusions:FAVS can effectively reduce indoor Rn and RnD concentrations by improving the air exchange,serving as a valuable supplement to existing radon mitigation methods,especially in extreme climates.

Wind-Thermal Environmental Characteristic of Multi-Variable Passive Enhanced Natural Ventilation System for High and Large Space Building

Natural ventilation effects in high and large space buildings of tropical areas greatlya ffect the air conditioning energy consumption.Aiming at nearly zero energy building design,thisp aper mainly contributes to provide theoretical basis and reference for thermal comfortable air conditioning system design of high and large space buildings.Taking a theatre in Hainan as study object,a newly composite enhanced natural ventilation system is proposed by integrating theu nderground tunnel-based earth to air heat exchange system and the solar chimney.Ventilationq uantity,air velocity and air temperature field,human vertical temperature gradient differenceu nder24simulation working conditions are considered and analyzed by using ANSYS Fluent.Fort he underground tunnel,results show that Group Two with double underground tunnels and side airs upply location shows its advantages in cooling effects and air supply uniformity.Then for the solar chimney,results show that the solar radiation intensity contributes to larger difference int ransmission power and leads to different cooling effects.On the whole,the system under workingc ondition No.7with120m long,side air supply,double underground tunnel and20m high,1mw ide,0.6°absorber plate angle solar chimney shows its priority in better comprehensive performance.

Organophosphate Esters in Air and Seawater of the South China Sea:Spatial Distribution,Transport,and Air−Sea Exchange

Organophosphate esters(OPEs)have become one group of chemicals with emerging concern in the marine environment.In this work,we investigated OPEs in the air and seawater of the South China Sea in summer 2019.The concentrations of∑_(10)OPEs in the atmosphere ranged from 66 to 550 pg/m^(3),with TCIPP,TNBP,TPhP,and TEP predominating in the air.The total dissolved OPE concentrations(∑_(10)OPEs without TEP)measured in high-volume water samples ranged from 300 to 3600 pg/L,with a mean concentration of 1180±910 pg/L.TEP was measured with liquid−liquid extraction(LLE),and it showed the highest concentration(average 2000±1450 pg/L)among the selected OPEs.Total suspended matter associated OPEs accounted for less than 4.7%of the sum of OPE concentrations in seawater.Fugacity fractions and air−sea exchange fluxes showed that TCEP,TCIPP,TIBP,TEHP,TPhP,and EHDPP were favored to volatilize,TEP dominated the deposition,while TPrP and TNBP varied between volatilization and deposition.Atmospheric particle deposition fluxes ranged from 5 to 71 ng/m^(2)/day with an average of 17±15 ng/m^(2)/day.The input of∑OPEs to the entire South China Sea via atmospheric particle deposition was estimated to be 22±19 tons/year,while the net air−sea exchange fluxes of OPEs were volatilization from seawater to air with an average of 44±33 tons/year.This work suggests that air−sea exchange and atmospheric particle deposition are significant processes interfering with the transport of OPEs in the marine environment.

Air–soil exchange of organochlorine pesticides in a sealed chamber

So far little is known about air–soil exchange under any sealed circumstances（e.g., in plastic and glass sheds）, which however has huge implications for the soil–air–plant pathways of persistent organic pollutants including organochlorine pesticides（OCPs）. A newly designed passive air sampler was tested in a sealed chamber for measuring the vertical concentration profiles of gaseous phase OCPs（hexachlorocyclohexanes（HCHs） and dichlorodiphenyltrichloroethanes（DDTs））. Air was sampled at 5, 15, and 30 cm above ground level every 10 th day during a 60-day period by deploying polyurethane foam cylinders housed in acrylonitrile butadiene styrene-covered cartridges. Concentrations and compositions of OCPs along the vertical sections indicated a clear relationship with proximity to the mixture of HCHs and DDTs which escapes from the soils. In addition, significant positive correlations were found between air temperatures and concentrations of HCHs and DDTs. These results indicated revolatilization and re-deposition being at or close to dynamic pseudo-equilibrium with the overlying air. The sampler used for addressing air–soil exchange of persistent organic pollutants in any sealed conditions is discussed.

NO_x Release from Snow and Ice Covered Surface in Polar Regions and the Tibetan Plateau

The exchanges of NOx between snow and air have significant impact on the atmospheric components and photochemical processes in the overlying boundary layer. Such exchanges increase the oxidizing capacity of the atmosphere and may have a crucial impact on the air signals that are retrieved from ice cores. In the recent years, sunlit snow and ice have been demonstrated to be important NOx sources in the polar atmospheric boundary layer. This paper makes a thorough review on the release of NOx from snow and ice, including field observations and experimental evidences, release mechanisms and influential parameters that affect such a release process, polar NOx concentrations and fluxes, and environmental impacts of the chemical processes of NOx in the polar atmospheric boundary layer. In the Tibetan Plateau, the released NOx observed recently in the sunlit snow/ice-cover is 1-order magnitude more than that in polar regions, but further scientific research is still needed to reveal its impact on the atmospheric oxidizing capacity.

Sensitivity analysis of the DehumReq model to evaluate the impact of predominant factors on dehumidification requirement of greenhouses in cold regions

In this study,the sensitivity of a novel dehumidification requirement model(DehumReq)is analyzed to evaluate the effect of the predominant factors on the dehumidification needs of the greenhouses.The hourly dehumidification demand and sensitivity coefficient(SC)are estimated for three different seasons:warm(July),mild(May),and cold(November),by using the local sensitivity analysis method.Based on SC values,the solar radiation,air exchange,leaf area index(LAI),and indoor setpoints(temperature,relative humidity(RH),and water vapor partial pressure(WVPP))have significant impact on the dehumidifi-cation needs,and the impact varies from season to season.Most parameters have a higher SC in summer,whereas solar radiation and LAI have a higher SC in mild season.The dehumidification load increases 4 times of its base value with increasing solar radiation by 200 W/m^(2),and the highest LAI(10)caused 5 times increment of the load.The changing of WVPP from its base value(1.5 kPa)to maximum(2.9 kPa)reduces the load 70%in summer.Air exchange was found to be the most crucial parameter because it is the main dehumidification approach that has a large range and is easily adjustable for any greenhouses.Sufficient air exchange by ventilation or infiltration will reduce the dehumidification load to zero in May and November and minimizes it to only nighttime load in July.For the other parameters,higher ambient air RH and indoor air speed will result in higher the dehumidification load;whereas higher inner surface condensation will result in lower dehumidifi-cation load.The result of this study will assist in the selection of the most efficient moisture control strategies and techniques for greenhouse humidity control.