Analysis Of Winter Formaldehyde And Vocs Pollution Characteristics Of Residential Kitchens In Severe Cold Regions And The Optimization Of Make-up Air

With the growth of national economy and the improvement of residents'living standard,people pay more and more attention to indoor air quality.The kitchen is the most polluted place in the residential building.The cooking method and make-up volume will affect the concentration of formaldehyde and VOCs in the kitchen.Effectively removing formaldehyde and VOCs and other pollutants in the kitchen,improving make-up air volume in the kitchen and optimizing cooking habits are of great significance for alleviating kitchen pollution in the cold regions.The problem of kitchen pollution is closely related to residents'health.In this paper,the characteristics of formaldehyde and VOCs pollution in residential kitchens in severe cold regions in northeast China in winter were studied by on-site measurement.We analyzed the source of each pollutant through on-site measurement.The influencing factors of formaldehyde and VOCs pollution were explored based on the experimental data of make-up air volume and questionnaire survey information.A total of 33 residential kitchens in three cities?Shenyang,Fushun and Yingkou?were selected as the samples.The concentration of formaldehyde and VOCs in closed conditions before cooking and during cooking were measured by gas chromatography mass spectrometry?GC-MS?,phenol reagent spectrophotometer and 2,4-dinitrophenylhydrazine?DNPH?sampling analysis,respectively.Ikair online integrated sensor and PPBRAE professional VOCs gas detector were used to track the change of formaldehyde and VOCs concentration during the test cooking,and meanwhile recorded the kitchen decoration,cooking oil type and other relevant information.As VOCs pollution in the kitchen in the severe cold area is more serious than other functional areas,the concentration of VOCs was tested under closed conditions of the kitchen,natural gas burning,release of natural gas and cooking.The source of pollutants was tracked.The data obtained from the test were used to objectively evaluate the air quality of the kitchen before cooking and during cooking by using the comprehensive index method.At the same time,the correlation between the temperature and humidity of the kitchen and the concentration of pollutants was analyzed.The lifetime cancer risk of formaldehyde and VOCs in the kitchen were calculated by using the method proposed by the environmental protection agency.According to the analysis results,it is speculated that the serious VOCs pollution in the kitchen is caused by incomplete natural gas combustion,natural gas leakage and cooking process.In addition,CO₂tracer gas method was used to test the air changes of the kitchen under daily cooking habits and the make-up air volume of the kitchen when the range hood was turned on at different window opening angles?15°,30°and 45°?.The network questionnaire was issued to investigate the current situation of the use of residential kitchen in the cold regions,and to compare the differences in the use habits of residential kitchen in the north and south.According to the investigation results,CFD simulation and on-site measurement results were compared under the infiltration condition of the kitchen and the opening window condition of different scales.At the same time,in order to explore the natural pressure difference under the most suitable kitchen in the cold region of the form of ceiling make-up air,we designed four types of ventilation.CFD simulation was used to analysis the temperature field and pollutant concentration in various forms,providing theoretical basis for improving the reasonable air distribution of residential kitchen in severe cold regions and creating a thermal comfortable environment suitable for kitchen staff.The results showed that the exceeding rate of formaldehyde in the kitchen was only 5.3%in the closed condition before cooking.The phenomenon of exceeding the standard is not very serious.However,the average VOCs concentration was 1.269mg/m³,higher than other functional spaces of residential buildings and higher than other climatic zones.During cooking,VOCs concentration is in a state of excess standard,mainly characterized by high concentration of toluene,D-limonene and butane,and there are aldehydes and ketones pollution.The change of formaldehyde and VOCs concentration during cooking is mainly related to residents'cooking methods.Frying produce more pollutants than steaming and boiling.Air quality is better under closed conditions before cooking.Most of them are in the clean and unpolluted state,some of them are in the light pollution.However,during the cooking period the kitchen is seriously polluted,most of them are in the light pollution and medium pollution level,some of them are in the heavy pollution.Correlation analysis showed that there was a weak correlation between pollutant concentration and air supplement.Humidity has a greater effect on pollutant concentration.According to the calculation,the lifetime carcinogenic risk of formaldehyde and benzene is 5.4×10^-6and 1.01×10^-6,respectively,which are both higher than the international carcinogenic risk standard value 1.0×10^-6stipulated by EPA.The risk is acceptable,but it exceeds the safety limit.Based on the experiment and numerical simulation,the air changes in the kitchen with opening window with variable scales ventilation is much higher than that infiltration ventilation alone.Ventilation can improve the emission of pollutants and heat.When the window is opened at 30°,it can meet the air volume demand of the winter kitchen in the severe cold regions.The results of the questionnaire showed that residents'cooking habits and ventilation habits are important factors leading to kitchen pollution.Through the analysis of the simulation results of the form of make-up air,the kitchen is in an uncomfortable state of negative pressure under the condition of infiltration,and the indoor temperature is low and air distribution is poor when the window is opened although the pollutants are well controlled.After the addition of make-up air opening,the air distribution is reasonable,and the static pressure in the kitchen fluctuates up and down at-19.66pa,without odor contamination.Indoor CO₂concentration fluctuates around 443ppm.It is an economical and applicable way to supplement wind in severe cold regions.