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Reducing human exposure to PM2.5 generated while cooking typical Chinese cuisine
Building and Environment 168 (2020) 106522
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Reducing human exposure to PM2.5 generated while cooking typical Chinese cuisine Yuejing Zhao a, Bin Zhao a, b, * a b
Department of Building Science, School of Architecture, Tsinghua University, Beijing, 100084, China Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Interventions Indoor air quality control Range hood Protective respirators Indoor air cleaner
Residential Chinese cooking can lead to severe exposure to carcinogenic fine particles (PM2.5) from cooking-oil fumes. Keeping the kitchen door open is conducive to improving air quality in the kitchen, but it can result in further diffusion of PM2.5 emissions into adjacent rooms. In this study, PM2.5 exposure concentrations were measured in the kitchen and an adjacent room during and after cooking activities, where various interventions were employed based on an orthogonal design. Intervention strategies, including range-hood operations, pro tective respirator use, personal portable fan operation, side panels configured for the range hood, and air cleaner use, were incorporated. The results demonstrated that using the range hood with an equivalent air exchange rate of 7.5–10.9 h 1 in the kitchen and wearing respirators during cooking were the most efficient prevention measures, significantly decreasing the inhalation exposure to PM2.5 for the cook in the kitchen by 90–95% and 79–84%, respectively. The average concentrations in the adjacent living room could be decreased by 50%–75% with an additional period of 5–10 min running the range hood or the air cleaner (the cleaner air exchange rate was no more than 5 h 1).
1. Introduction Cooking has been identified as a major source of indoor particulate matter, particularly in Chinese households [1,2]. Compared to western cooking, household air pollution caused by Chinese cooking is severe, given the particularity and complexity of Chinese cuisine [3–6]. Because cooking is a daily practice in most Chinese households, it exerts a sig nificant influence on indoor residential air quality. It has been found that temperatures over 170 � C, which are required for some traditional Chinese cooking methods (e.g., stir-frying, pan-frying, and deep-frying) generate high levels of fine particulate matter (PM2.5) [6,7]. Studies have indicated an association between the development of lung cancer among Chinese women, including non-smoking women, and exposure to these cooking oil fumes [8–13]. Moreover, organic compounds, such as particle-bound polycyclic aromatic hydrocarbons and inorganic con stituents, such as heavy metals, that adsorb onto large surface areas of PM2.5 may be harmful to human health and have been identified as carcinogens [14]. Previous studies have shown that the average PM2.5 concentration in a kitchen can exceed 300 μg/m3, even with adequate ventilation [2,6]. Therefore, reducing personal exposure to PM2.5 during cooking is essential for the health of Chinese residents.
Several studies have focused on methods of removing cooking emissions, including upgrading ventilation systems concerned with airflow patterns [15–17]. Previously, Cao, et al. [16] investigated the exposure-level reduction effectiveness of a local make-up airflow through both upward and downward air supplies. Those researchers found that the individual exposure level could be reduced by 2–3 orders of magnitude compared with the condition in which all make-up air came from an open window. Additionally, the use of an air curtain as a kitchen air source in both upward or downward modes has been well studied [18,19]. Such studies have investigated the effects of air-curtain jet velocity, the jet angle, jet-slot width, and the area of the guide plate [20]. Furthermore, resident behavior with respect to kitchen ventilation in residential buildings has been associated with improvements in kitchen indoor air quality [21–23]. However, these practices are diffi cult to implement because of the reconstruction requirements. Furthermore, previous studies have not focused on residential exposure in actual household cooking situations using low-cost interventions. Currently, the range hood is commonly used to discharge PM2.5 emissions from the kitchen. On one hand, this device removes air pol lutants near the emission source directly. On the other, mechanical ventilation via the range hood can help increase the total air exchange
* Corresponding author. Dept. of Building Science, School of Architecture, Tsinghua University, Beijing, China. E-mail address: [email protected] (B. Zhao). https://doi.org/10.1016/j.buildenv.2019.106522 Received 7 July 2019; Received in revised form 11 October 2019; Accepted 30 October 2019 Available online 4 November 2019 0360-1323/© 2019 Elsevier Ltd. All rights reserved.
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kitchen during cooking can be elevated to over 500 μg/m3 if the venti lation is poor [6]. Therefore, ensuring good ventilation, such as by keeping the kitchen door open when cooking, is significant for improving kitchen air quality. However, this kind of ventilation can deteriorate the air quality of the adjacent rooms [32]. Previous research has mainly employed single strategies for reducing PM2.5 exposure, emphasizing either enhancements to range-hood per formance or improvements of air flow, rather than combinations of various cheap interventions. Moreover, these studies tended to be
rate of the residence. However, the performance of the range hood is limited by factors, such as the type, air-flow velocity, heat production, aerodynamic design, and space position [24–30]. Some overhead island range hoods can achieve a capture efficiency of up to 95% with high flow rates exceeding 680 m3/h [31]. However, the practical capture efficiency of a wall-mounted range hood is generally less than 75% [6], implying a limited pollution discharge capacity. Thus, not all particulate matter can be discharged effectively. Some field studies have shown that, even with the range hood activated, the PM2.5 concentration in a Table 1 Orthogonal design table of interventions.
a
Numbers highlighted in red indicate that the corresponding experiment was conducted under the same test conditions, except with the kitchen-door closed. A dummy blank factor was considered simultaneously for error estimation. c The listed mode represents the operational status during cooking. HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed; ACO: air cleaner off; ACL: air cleaner on at low speed; ACH: air cleaner on at high speed. d RO: respirator off; KN: KN95 respirator; KP: KP95 respirator. e FO: portable fan off; FL: portable fan on at low speed; FH: portable fan on at high speed. f SP height indicates the height of the two side panels. g This duration refers to the running duration after the cooking activities were complete. b
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conducive to ventilation design during the pre-construction stages of new buildings and for reference when purchasing a new range hood. However, they are not very helpful for most old residences, given the reconstruction work required to adopt the strategies. Hence, an objec tive of this study is to investigate the control effect of combined in terventions under various strategies based on an orthogonal test design by measuring inhalation exposures to PM2.5 in real residential cooking conditions. Another objective is to determine the most effective means of reducing exposure to cooking-related PM2.5 in the kitchen and adja cent rooms (i.e., living room) that are cost-efficient and free of reno vation requirements.
(Columns 3–7 in Table 1) and another for the post-cooking period (the last 2 columns in Table 1). In total, 24 sets of experiments were estab lished, comprising 18 open-kitchen-door cases and 6 closed-kitchen-door cases. 2.2. Instrumentation and measurements A residential kitchen equipped with two gas stoves in Beijing was chosen for the experiments, which were performed between November 3, 2018, to December 9, 2018. Because the forced ventilation pre dominated when the range hood was in operation, seldom impacted by the indoor and outdoor temperature differences, the period of the year with higher outdoor temperatures was not covered in this study. Fig. 1 shows the layout of the kitchen, and the schematic of the measurement apparatuses can be found in the Supplementary Materials (Fig. S1). A wall-mounted range hood that had been used for more than 10 years was located near the kitchen door to discharge the cooking-oil fumes. The flow rates of the range hood were measured in situ before each cooking test by multiplying the kitchen volume (11.25 m3) and the air-exchange rate (h 1) obtained via the CO2-decay method. The average flow rates of the kitchen exhaust hood for the low- and high-fan-speed settings were determined to be 84 and 123 m3/h, respectively (Table S1). The air exchange in the living room (volume of 47.62 m3) comprised the makeup air being pulled from the other connected zone or that which infil trated through the closed windows with no air conditioning. Two laser photometers, each equipped with a 2.5-μm impactor (AM510; TSI Inc., Shoreview, MN, USA), were used to monitor the real-time mass con centrations of PM2.5. One of the photometers was placed at a height of approximately 1.2 m (close to the height of the breathing zone when an occupant sits) in the living room. The other was carried in a shoulder brace in the vicinity of the cook’s breathing zone in the kitchen, which was roughly 0.15-m away from, but on the same horizontal plane as the cook’s nose. In the following discussion, the measured PM2.5 levels from the two instruments are referred to as “exposure concentrations” in the living room and the kitchen, because they precisely reflect the PM2.5 concentrations in the breathing zone. The two photometers were cali brated before the experiments. Calibration details can be found in the Supplementary Materials, Fig. S2. The personal portable fan fixed on a shoulder strap around the cook’s chest, 1.2 m above the floor, was operated at a high speed of 3.5 m/s or at a low speed of 2 m/s, where the airflow from the fan was in a vertical direction, as shown in Fig. S1. The two types of non-powered air-purifying particle respirator, KN95 and
2. Methods 2.1. Orthogonal test design As reported in previous studies, the range hood is a conventional tool for re-routing cooking-oil fumes during cooking. Additionally, side panels mounted beneath the hood baffle are used indigenously to block the escape of cooking emissions in traditional houses. Furthermore, the reduction of harmful emissions actually inhaled by occupants at the kitchen countertop while cooking should also be considered. Because face masks are widely used in some construction works to protect from PM2.5 air pollution [33], these devices were considered as a prevention measure in our experiment design. Thus, two types of non-powered air-purifying particle respirators, KN95 (SZ5107; EPC, Beijing, China) and KP95 (EPR HH-10; EPC, Beijing, China), were used. The other two control strategies included carrying a two-speed personal portable fan at the breathing zone when cooking and the activation of an air cleaner having a two-shift operation mode (i.e., high and low speeds) to remove the dispersed cooking-emitted PM2.5 from the living room. For the post-cooking period, when the stove was deactivated after cooking completion, the range hood or air cleaner was either deactivated (duration ¼ 0 min) or left on for an additional period (5–10 min at high speed) with the kitchen door open, to investigate the effect on the PM2.5 levels in the living room. Thus, an L18 (2 � 37) orthogonal experiment, which can efficiently handle multifactor experiments by adopting a minimum number of tests, was performed to obtain the optimal ar rangements for all interventions designed to effectively lower PM2.5 exposure in the kitchen and living room. The schemes of the orthogonal experiment are listed in Table 1. In our experimental design, the in terventions were separated into two parts: one for the cooking period
Fig. 1. Diagram of the testing room and the location of sampling points (unit: cm). 3
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KP95 (specialized for preventing oil particles), were connected to the AM510 air inlet through a 30-cm-long antistatic silicone tube inserted with a sample probe (8025-N95; TSI Inc., Shoreview, MN, USA) to obtain PM2.5 exposure concentrations. A household air cleaner was placed approximately 0.5 m from the measuring point on the floor of the living room. The clean air delivery rates were found to be 18 and 268 m3/h (a clean air exchange rate of ~5 h 1) for low and high air volumes, respectively. An average of 6 tests per day were completed with a time interval of at least 3 days before the next test day. The protocol for each cooking test was as follows. First, the background PM2.5 levels were measured for 15 min before cooking was initiated; the range hood was operated at the designed fan speed settings (i.e., off, low speed, or high speed) for the subsequent cooking stage. To obtain the exact PM2.5 emissions caused by cooking when analyzing the measurement data, the PM2.5 contribution of the make-up air entering the test rooms was eliminated by subtracting the background PM2.5 concentrations. Then, the cooking activity (i.e., frying of mutton with shallots for 3.8 min) was conducted under the designed test conditions with interventions detailed in the orthogonal table. After the stove was deactivated following cooking completion, the range hood or air cleaner was either deactivated or left on for an addi tional duration as described in the orthogonal test design. The PM2.5 concentrations were sequentially monitored during cooking and for 10 min after the cooking period. Between each experiment, the kitchen was forcibly ventilated for at least 45 min by operating the range hood and opening all the windows to ensure that the PM2.5 concentration returned to the background level. The air exchange rate (AER) for each ventilation pattern was also determined via the CO2-decay method, where the baseline concentrations before and after each measurement were averaged. The AERs of the kitchen with the kitchen door open and closed were 3.11 � 0.53 and 1.74 � 0.15 h 1, respectively.
returned to the background level between each experiment. All windows and interior doors, excluding the kitchen door, were closed during the tests to minimize air exchange in the house, aside from that generated by the exhaust hood. 3. Results 3.1. Control effect of intervention measures 3.1.1. Kitchen Fig. 2 shows that, among the controls, the range hood provided the most protection, reducing exposure concentrations by a factor of ~10 for otherwise similar conditions. The use of a mask appears to have reduced concentrations by a factor of 3–5. The reduction in the average PM2.5 exposure concentrations in the kitchen during the cooking period was mainly attributed to range-hood operation and respirator use. These measures appear to be the most effective methods of handling PM2.5 exposure. The fan had a relatively small effect: on the order of 10% or less. More specific results are shown in Tables S4 and S5 of the Sup plementary Materials. The results varied from 0.017 to 2.176 mg/m3 with different interventions, where a combination of wearing a mask and operating both the range hood and the portable fan at high speed was proven to be the most efficient measure for reducing PM2.5 expo sure. The average PM2.5 exposure concentrations with a range hood and respirator employed separately were approximately 200 and 400 μg/m3, respectively. The exposure concentrations dropped significantly with the use of the range hood, and a decreasing trend was observed when an air-purifying particle respirator was equipped for both masks evaluated in this study. However, the effect of wearing a respirator was less remarkable that of range-hood operation, which could possibly be attributed to the lower-measured respirator efficiencies (88% for KN and 92% for KP, as shown in Fig. 3) compared to the nominal efficiency (95%). Additionally, application of a portable fan in the vicinity of the breathing zone likely decreased the exposure levels in general, espe cially when the range hood was kept off.
2.3. Quality assurance and control The same dish of fried mutton with shallots chosen for all cooking tests was cooked by a professional chef, who used the same cooking utensils and followed an identical cooking procedure in each case (Table S2 in the Supplementary Materials) with a stopwatch to ensure repeatability. The dish, which involved 360 g of food ingredients, is suitable for families of 3–4 persons, and was suggested by our profes sional chef to provide a common cooking scenario for most Chinese residences. It was also selected as a typical Chinese dish based on an online survey of 309 Chinese families conducted by Chen et al. [6] (specific results can be found in Table S3). For each test, the food in gredients were weighed in advance on an electronic scale having an accuracy of 0.001 g. All food ingredients were placed within reach to reduce the movements of the cook, and the timekeeper inside the kitchen during the measurement stood away from the cooktop, almost motionlessly. Thus, the movement of the occupants can be neglected. Each room in the flat was equipped with heating radiators, and the temperatures varied within a narrow range of 20.2–22.5 � C. The relative humidity in the kitchen changed from 32 to 46% during the experiment period (Fig. S3). Each set of designed conditions (the 18 open-door cases and 6 closed-door cases) was repeated twice for a total of 48 cooking tests. The relative deviation of the repeated experiments ranged from 1 to 20%, as shown in the Supplementary Materials (Fig. S4). Addition ally, the two AM510 photometers were calibrated before testing, and a set of comparisons between the two instrument readings, ranging from 0.4 to 3.2 mg/m3, was performed for concentration measurement. The relative correlation for the concentration curve between the 2 a.m.510 photometers was higher than 0.98 (R2 ¼ 0.981). Before the experiments, the exposure concentrations for the cook wearing a mask were moni tored. During the test, the cook adjusted the mask to perfectly attach onto his face until the AM510 readings yielded 0 μg/m3, indicating that the mask was sufficiently sealed in consideration of data validity. The kitchen was force-ventilated to ensure that the PM2.5 concentration
3.1.2. Living room Regarding the living room, the average concentrations during entire period of cooking and post-cooking were 0.282–1.187 mg/m3 with the range hood off during cooking, roughly 20 times those when the range hood was running (0.010–0.068 mg/m3). The increase of PM2.5 con centrations during cooking generally rose ~3 min after cooking started. Recall that the entire cooking period was 3.8 min. This addresses the time lapse for PM2.5 pervasion. As shown in Fig. S5, the PM2.5 concen tration in the living room continued to increase for approximately 3–4 min after cooking was finished, and then decayed with time. How ever, on condition that the range hood was running during cooking time, the PM2.5 levels in the living room tended to be stable before the mea surement for post-cooking period ended. Notably, the PM2.5 concen trations can exceed 1.700 mg/m3 if no intervention is performed, as shown in Fig. 4. It was quite apparent that, during the cooking period, the air quality in the living room seldom was affected when the range hood was running. The results shown in Fig. 4 for the living room show that range hood operation was the most effective intervention by far, reducing peak concentrations by a factor of 50–100. With the hood off, operating the air cleaner on high appears to have ~22% effect. Simi larly, the results in Fig. 5 indicate that using a range hood during cooking, irrespective of the speed setting, which contributed ~95% benefit, was much more effective compared to post-cooking in terventions (namely the range hood or air cleaner was left running for an additional period of 5–10 min). By contrast, a decrease of 50%–75% was observed with the application of these post-cooking interventions. The average PM2.5 concentrations in the living room during the entire period ranged from 0.250 to 0.650 mg/m3, indicating that an air cleaner with a clean air exchange rate of ~5 h 1 was not enough to remove cooking emissions effectively. There was a downward trend as the running 4
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Fig. 2. PM2.5 exposure concentration in kitchen during cooking with kitchen-door open (FO: portable fan off; FL: portable fan on at low speed; FH: portable fan on at high speed; RO: respirator off; KN: KN95 respirator; KP: KP95 respirator; HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed).
corresponding reductions were slightly lower when a respirator was worn (80% for KN95 and 83% for KP95). Moreover, the PM2.5 exposure for the cook was reduced by up to 98% when both interventions were applied simultaneously. The removal efficiency of the range hood in this study was determined to be consistent with the results of Poon et al. [34] (87–92%), but much higher than that reported by Chen et al. [6] (52–63%), despite the fact that a higher exhaust rate was used in their experiments (233 m3/h). The PM2.5 concentration distribution in the kitchen was non-uniform when the range hood was kept off. However, in the study by Chen et al. [6], two fans were used to ensure proper mixing of air. Thus, the exposure concentrations obtained with no in terventions, which were considered a benchmark in the reduction cal culations, could be elevated to a higher level. This behavior could likely explain the higher reduction measured in that study. Furthermore, the average exposure concentrations in the open-door cases were generally 10% lower than those of closed-door cases (Fig. S8 of the Supplementary Materials). This is consistent with the findings in the study of Zhou et al. [35].
Fig. 3. Filter efficiency of the two types of non-powered air-purifying particle respirators.
3.2. Significance analysis of interventions Range-hood operation and respirator user were statistically signifi cant interventions affecting the PM2.5 exposure concentrations, compared to the results obtained using a portable fan or by configuring the range hood with side panels (Fig. 6). The range of influence on the air distribution created by the portable fan was relatively smaller than that with the range hood. Moreover, the average PM2.5 exposure for the cook registered an approximate 13% reduction when employing the portable fan at high speeds. However, it was not statistically significant. The reductions observed when the kitchen door was kept open while cooking were statistically significant. Operating the range hood at a high or low speed while wearing a KP95 respirator contributed to effective PM2.5 exposure reduction with a significant difference level of 0.01, in contrast to the significance at a level of 0.05 achieved when wearing a KN95 respirator. No significant difference was observed between the results measured with high- and low-speed settings for the range hood in this study. This is likely due to their similar exhaust rates (123 and 84 m3/h for high and low speeds, respectively, with a relative error <6.4%).
duration of the air cleaner or the range hood increased if the range hood was not used when cooking. The average concentrations in the living room were 7.4% those in the kitchen when the range hood was operated continuously, and 29% those in the kitchen if the range hood was deactivated. Moreover, configuring the side panels for the range hood may have slightly reduced the PM2.5 concentrations in the living room when the range hood remained off during the cooking period (see Fig. 4) Although the average PM2.5 concentrations in the living room were much lower than those of the kitchen during the cooking period, a sta tistically significant increase of 2–20 times was observed during the post-cooking period compared to the cooking period, as shown in Fig. S6. These findings indicate that the PM2.5 emissions remaining in the kitchen could subsequently diffuse into the living room, even with continuous operation of the range hood after cooking, demonstrating that one can abate PM2.5 pollution in the living room by closing the kitchen door immediately after the cooking activities are complete. 3.1.3. Reduction percentage As shown in Supplementary Materials, Fig. S7, the average exposure concentrations could be reduced by 90 and 93% (mean values) using a range hood at low and high flow rates, respectively. However, the 5
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Fig. 4. Peak concentrations of PM2.5 in the living room during cooking (0 cm: the height of the two side panels is 0 cm; 12 cm: the height is 12 cm; 24 cm: the height is 24 cm; ACO: air cleaner off; ACL: air cleaner on at low speed; ACH: air cleaner on at high speed; HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed).
Fig. 5. Average concentrations of PM2.5 in the living room during entire period of cooking and post-cooking (0 cm: the height of the two side panels is 0 cm; 12 cm: the height is 12 cm; 24 cm: the height is 24 cm; AC duration: air cleaner running duration; Range hood duration: the running duration of range hood).
4. Discussion
closing the kitchen door after cooking to restrain the subsequent dispersion of PM2.5 into the adjacent room, rather than leaving the range hood on, is overall more effective and energy-saving.
4.1. Recommendations to reduce exposure to PM2.5 from cooking The results demonstrate that a low hood-flow rate can be partially compensated by wearing a respirator during cooking, which is costeffective and avoids the inconvenience of ventilation retrofits. Thus, range hood operation at a relatively low flow rate during cooking could be considered sufficient for reducing the cook’s exposure to PM2.5 to an acceptable level, provided a respirator is used simultaneously. Given the discomfort of wearing a respirator, we believe that it should serve as an auxiliary means of partially compensating for low flow rates for resi dents who do not perform retrofit works, such as with the configuration of a new range hood with a sufficiently high flow rate or removal effi ciency. Meanwhile, PM2.5 concentrations in the kitchen can be reduced by keeping the kitchen door open when cooking. The adverse effects in the adjacent room can be reduced by using a range hood. Nonetheless,
4.2. Limitations and prospective research The present study has several limitations. The cooking activity con ducted in this study lasted for a short time of 3.8 min and was composed of only one typical dish, in consideration of the fact that a more complex cooking procedure could add to uncertainty of the experiment results. However, the representativeness of the chosen dish was ensured based on an online survey about cooking behaviors of Chinese residents (Tables S3–(a)-(e)). Besides, only a limited post-cooking period of 10 min was taken into account in this study. However, it was supposed as a reasonable course of action, considering that most Chinese residents would leave the range hood running no more than 15 min according to our previous survey as shown in Tables S3–(e), which was also 6
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Fig. 6. Control effect comparison based on statistical significance analysis (average PM2.5 exposure concentrations in the kitchen during cooking were applied).
consistent with the study of Dobbin et al. [22]. This study focused on interventions free of reconstruction work in existing buildings. Nevertheless, further studies on various ventilation systems are of significance for ventilation design in the pre-construction stages of new buildings, because this is an effective means of improving indoor air quality [36]. Further efforts to enhance extraction-hood ef ficiency are also essential, because respirator wearing may be uncom fortable. Furthermore, the uncertainties concerning some experimental variables (e.g., cooking type and the range hood flow rate) should be considered in future investigations.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by grants from the National Key Research and Development Program of China [grant number 2017YFC0702700] and the Innovative Research Groups of the National Natural Science Foundation of China [grant number 51521005].
5. Conclusions
Appendix A. Supplementary data
In this study, PM2.5 exposure concentrations caused to cooking ac tivities were measured to investigate the utility of multiple interventions based on an orthogonal design. The average PM2.5 exposure concen trations during cooking ranged from 0.017 to 0.473 mg/m3 with a range hood or respirators employed. The results indicated that running the range hood and wearing respirators during cooking decreased the inhalation exposure to PM2.5 in a statistically significant manner, where the reduction percentage was 90–95% and 79–84%, respectively. By contrast, the effect of using a portable fan or configuring side panels for the range hood did not reach statistical significance. Moreover, a scarce increase of PM2.5 concentrations in the living room during a cooking period of 3.8 min occurred when running the range hood with the kitchen door open, which could then be elevated to a much higher level during a post-cooking period of 10 min. The average PM2.5 levels in the adjacent living room could be lowered by 50%–75% with an additional period of 5–10min running the range hood or the air cleaner. In com parison, it would make an improvement of more than 95% if the range hood was remained on during cooking time. These findings provide helpful recommendations to Chinese residents to protect from cookingrelated PM2.5 exposure via low-cost interventions and appropriate cooking behaviors.
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Notes The authors declare no competing financial interest. Competing financial interests The authors have declared that they have no actual or potential competing financial interests. 7
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Building and Environment 168 (2020) 106522 [24] D. Rim, L. Wallace, S. Nabinger, A. Persily, Reduction of exposure to ultrafine particles by kitchen exhaust hoods: the effects of exhaust flow rates, particle size, and burner position, Sci. Total Environ. 432 (2012) 350–356. [25] B.C. Singer, W.W. Delp, P.N. Price, M.G. Apte, Performance of installed cooking exhaust devices, Indoor Air 22 (3) (2012) 224–234. [26] L.C. Tseng, C.C. Chen, Effect of flow characteristics on ultrafine particle emissions from range hoods, Ann. Occup. Hyg. 57 (7) (2013) 920–933. [27] M.M. Lunden, W.W. Delp, B.C. Singer, Capture efficiency of cooking-related fine and ultrafine particles by residential exhaust hoods, Indoor Air 25 (1) (2015) 45–58. [28] B.C. Singer, R.Z. Pass, W.W. Delp, D.M. Lorenzetti, R.L. Maddalena, Pollutant concentrations and emission rates from natural gas cooking burners without and with range hood exhaust in nine California homes, Build. Environ. 122 (2017) 215–229. [29] Y.C. Zhang, T. Wang, X.Q. Liu, Y.D. Zhu, Y.X. Yang, Simulation analysis and experimental study of the cooker hoods of high-rise residential buildings, Appl. Sci. Basel 8 (5) (2018) 16. [30] Y.J. Zhao, A.G. Li, P.F. Tao, R. Gao, The impact of various hood shapes, and side panel and exhaust duct arrangements, on the performance of typical Chinese style cooking hoods, Build. Simul. 6 (2) (2013) 139–149. [31] J.D. Clark, G. Rojas, I.S. Walker, Towards the development of a standardized testing protocol for overhead island kitchen exhaust devices: procedures, measurements and paths forward, Build. Environ. 142 (2018) 301–311. [32] A.C.K. Lai, Y.W. Ho, Spatial concentration variation of cooking-emitted particles in a residential kitchen, Build. Environ. 43 (5) (2008) 871–876. [33] V. Azarov, S. Manzhilevskaya, L. Petrenko, The pollution prevention during the civil construction, MATEC Web Conf. 196 (2018), 04073. [34] C. Poon, L. Wallace, A.C.K. Lai, Experimental study of exposure to cooking emitted particles under single zone and two-zone environments, Build. Environ. 104 (2016) 122–130. [35] B. Zhou, P. Wei, M.L. Tan, Y. Xu, L.L. Ding, X.Y. Mao, Y.K. Zhao, R. Kosonen, Capture efficiency and thermal comfort in Chinese residential kitchen with pushpull ventilation system in winter-a field study, Build. Environ. 149 (2019) 182–195. [36] Analysis of the Dust Particles Distribution and Ventilation as a Way to Improve Indoor Air Quality, Analysis Of the Dust Particles Distribution and Ventilation as a Way to Improve Indoor Air Quality IN Energy Management Of Municipal Transportation Facilities And Transport Energy Management of Municipal Transportation Facilities and Transport, 2017.
[11] X.R. Wang, Y.L. Chiu, H. Qiu, J.S.K. Au, I.T.S. Yu, The roles of smoking and cooking emissions in lung cancer risk among Chinese women in Hong Kong, Ann. Oncol. 20 (4) (2009) 746–751. [12] T.J. Wang, B.S. Zhou, J.P. Shi, Lung cancer in nonsmoking Chinese women: a casecontrol study, Lung Cancer 14 (1996) S93–S98. [13] A. Seow, W.T. Poh, M. Teh, P. Eng, Y.T. Wang, W.C. Tan, M.C. Yu, H.P. Lee, Fumes from meat cooking and lung cancer risk in Chinese women, Cancer Epidemiol. Biomark. Prev. 9 (11) (2000) 1215–1221. [14] IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, A Review Of Human Carcinogens: Arsenic, Metals, Fibres, and Dusts IN IARC Monographs On the Evaluation Of Carcinogenic Risks To Humans IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, International Agency for Research on Cancer, Lyon, France, 2012. [15] S.H. Jeong, H.M. Kwon, S.J. Ahn, J.H. Yang, A study on the improvement of ventilation rate using air-flow inducing local exhaust ventilation system, J. Asian Architect. Build Eng. 15 (1) (2016) 119–126. [16] C.S. Cao, J. Gao, L. Wu, X.H. Ding, X. Zhang, Ventilation improvement for reducing individual exposure to cooking-generated particles in Chinese residential kitchen, Indoor Built Environ. 26 (2) (2017) 226–237. [17] A.C.K. Lai, Modeling of airborne particle exposure and effectiveness of engineering control strategies, Build. Environ. 39 (6) (2004) 599–610. [18] C.H. Pan, T.S. Shih, C.J. Chen, J.H. Hsu, S.C. Wang, C.P. Huang, C.T. Kuo, K.Y. Wu, H. Hu, C.C. Chan, Reduction of cooking oil fume exposure following an engineering intervention in Chinese restaurants, Occup. Environ. Med. 68 (1) (2011) 10–15. [19] B. Zhou, F. Chen, Z.B. Dong, P.V. Nielsen, Study on pollution control in residential kitchen based on the push-pull ventilation system, Build. Environ. 107 (2016) 99–112. [20] X.M. Liu, X. Wang, G. Xi, Orthogonal design on range hood with air curtain and its effects on kitchen environment, J. Occup. Environ. Hyg. 11 (3) (2014) 186–199. [21] H. Lee, Y.J. Lee, S.Y. Park, Y.W. Kim, Y. Lee, The improvement of ventilation behaviours in kitchens of residential buildings, Indoor Built Environ. 21 (1) (2012) 48–61. [22] N.A. Dobbin, L. Sun, L. Wallace, R. Kulka, H.Y. You, T. Shin, D. Aubin, M. St-Jean, B.C. Singer, The benefit of kitchen exhaust fan use after cooking - an experimental assessment, Build, Environ. Times 135 (2018) 286–296. [23] M.A. Johnson, R.A. Chiang, Quantitative stove use and ventilation guidance for behavior change strategies, J. Health Commun. 20 (2015) 6–9.
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Reducing human exposure to PM2.5 generated while cooking typical Chinese cuisine Yuejing Zhao a, Bin Zhao a, b, * a b
Department of Building Science, School of Architecture, Tsinghua University, Beijing, 100084, China Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Interventions Indoor air quality control Range hood Protective respirators Indoor air cleaner
Residential Chinese cooking can lead to severe exposure to carcinogenic fine particles (PM2.5) from cooking-oil fumes. Keeping the kitchen door open is conducive to improving air quality in the kitchen, but it can result in further diffusion of PM2.5 emissions into adjacent rooms. In this study, PM2.5 exposure concentrations were measured in the kitchen and an adjacent room during and after cooking activities, where various interventions were employed based on an orthogonal design. Intervention strategies, including range-hood operations, pro tective respirator use, personal portable fan operation, side panels configured for the range hood, and air cleaner use, were incorporated. The results demonstrated that using the range hood with an equivalent air exchange rate of 7.5–10.9 h 1 in the kitchen and wearing respirators during cooking were the most efficient prevention measures, significantly decreasing the inhalation exposure to PM2.5 for the cook in the kitchen by 90–95% and 79–84%, respectively. The average concentrations in the adjacent living room could be decreased by 50%–75% with an additional period of 5–10 min running the range hood or the air cleaner (the cleaner air exchange rate was no more than 5 h 1).
1. Introduction Cooking has been identified as a major source of indoor particulate matter, particularly in Chinese households [1,2]. Compared to western cooking, household air pollution caused by Chinese cooking is severe, given the particularity and complexity of Chinese cuisine [3–6]. Because cooking is a daily practice in most Chinese households, it exerts a sig nificant influence on indoor residential air quality. It has been found that temperatures over 170 � C, which are required for some traditional Chinese cooking methods (e.g., stir-frying, pan-frying, and deep-frying) generate high levels of fine particulate matter (PM2.5) [6,7]. Studies have indicated an association between the development of lung cancer among Chinese women, including non-smoking women, and exposure to these cooking oil fumes [8–13]. Moreover, organic compounds, such as particle-bound polycyclic aromatic hydrocarbons and inorganic con stituents, such as heavy metals, that adsorb onto large surface areas of PM2.5 may be harmful to human health and have been identified as carcinogens [14]. Previous studies have shown that the average PM2.5 concentration in a kitchen can exceed 300 μg/m3, even with adequate ventilation [2,6]. Therefore, reducing personal exposure to PM2.5 during cooking is essential for the health of Chinese residents.
Several studies have focused on methods of removing cooking emissions, including upgrading ventilation systems concerned with airflow patterns [15–17]. Previously, Cao, et al. [16] investigated the exposure-level reduction effectiveness of a local make-up airflow through both upward and downward air supplies. Those researchers found that the individual exposure level could be reduced by 2–3 orders of magnitude compared with the condition in which all make-up air came from an open window. Additionally, the use of an air curtain as a kitchen air source in both upward or downward modes has been well studied [18,19]. Such studies have investigated the effects of air-curtain jet velocity, the jet angle, jet-slot width, and the area of the guide plate [20]. Furthermore, resident behavior with respect to kitchen ventilation in residential buildings has been associated with improvements in kitchen indoor air quality [21–23]. However, these practices are diffi cult to implement because of the reconstruction requirements. Furthermore, previous studies have not focused on residential exposure in actual household cooking situations using low-cost interventions. Currently, the range hood is commonly used to discharge PM2.5 emissions from the kitchen. On one hand, this device removes air pol lutants near the emission source directly. On the other, mechanical ventilation via the range hood can help increase the total air exchange
* Corresponding author. Dept. of Building Science, School of Architecture, Tsinghua University, Beijing, China. E-mail address: [email protected] (B. Zhao). https://doi.org/10.1016/j.buildenv.2019.106522 Received 7 July 2019; Received in revised form 11 October 2019; Accepted 30 October 2019 Available online 4 November 2019 0360-1323/© 2019 Elsevier Ltd. All rights reserved.
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kitchen during cooking can be elevated to over 500 μg/m3 if the venti lation is poor [6]. Therefore, ensuring good ventilation, such as by keeping the kitchen door open when cooking, is significant for improving kitchen air quality. However, this kind of ventilation can deteriorate the air quality of the adjacent rooms [32]. Previous research has mainly employed single strategies for reducing PM2.5 exposure, emphasizing either enhancements to range-hood per formance or improvements of air flow, rather than combinations of various cheap interventions. Moreover, these studies tended to be
rate of the residence. However, the performance of the range hood is limited by factors, such as the type, air-flow velocity, heat production, aerodynamic design, and space position [24–30]. Some overhead island range hoods can achieve a capture efficiency of up to 95% with high flow rates exceeding 680 m3/h [31]. However, the practical capture efficiency of a wall-mounted range hood is generally less than 75% [6], implying a limited pollution discharge capacity. Thus, not all particulate matter can be discharged effectively. Some field studies have shown that, even with the range hood activated, the PM2.5 concentration in a Table 1 Orthogonal design table of interventions.
a
Numbers highlighted in red indicate that the corresponding experiment was conducted under the same test conditions, except with the kitchen-door closed. A dummy blank factor was considered simultaneously for error estimation. c The listed mode represents the operational status during cooking. HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed; ACO: air cleaner off; ACL: air cleaner on at low speed; ACH: air cleaner on at high speed. d RO: respirator off; KN: KN95 respirator; KP: KP95 respirator. e FO: portable fan off; FL: portable fan on at low speed; FH: portable fan on at high speed. f SP height indicates the height of the two side panels. g This duration refers to the running duration after the cooking activities were complete. b
2
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conducive to ventilation design during the pre-construction stages of new buildings and for reference when purchasing a new range hood. However, they are not very helpful for most old residences, given the reconstruction work required to adopt the strategies. Hence, an objec tive of this study is to investigate the control effect of combined in terventions under various strategies based on an orthogonal test design by measuring inhalation exposures to PM2.5 in real residential cooking conditions. Another objective is to determine the most effective means of reducing exposure to cooking-related PM2.5 in the kitchen and adja cent rooms (i.e., living room) that are cost-efficient and free of reno vation requirements.
(Columns 3–7 in Table 1) and another for the post-cooking period (the last 2 columns in Table 1). In total, 24 sets of experiments were estab lished, comprising 18 open-kitchen-door cases and 6 closed-kitchen-door cases. 2.2. Instrumentation and measurements A residential kitchen equipped with two gas stoves in Beijing was chosen for the experiments, which were performed between November 3, 2018, to December 9, 2018. Because the forced ventilation pre dominated when the range hood was in operation, seldom impacted by the indoor and outdoor temperature differences, the period of the year with higher outdoor temperatures was not covered in this study. Fig. 1 shows the layout of the kitchen, and the schematic of the measurement apparatuses can be found in the Supplementary Materials (Fig. S1). A wall-mounted range hood that had been used for more than 10 years was located near the kitchen door to discharge the cooking-oil fumes. The flow rates of the range hood were measured in situ before each cooking test by multiplying the kitchen volume (11.25 m3) and the air-exchange rate (h 1) obtained via the CO2-decay method. The average flow rates of the kitchen exhaust hood for the low- and high-fan-speed settings were determined to be 84 and 123 m3/h, respectively (Table S1). The air exchange in the living room (volume of 47.62 m3) comprised the makeup air being pulled from the other connected zone or that which infil trated through the closed windows with no air conditioning. Two laser photometers, each equipped with a 2.5-μm impactor (AM510; TSI Inc., Shoreview, MN, USA), were used to monitor the real-time mass con centrations of PM2.5. One of the photometers was placed at a height of approximately 1.2 m (close to the height of the breathing zone when an occupant sits) in the living room. The other was carried in a shoulder brace in the vicinity of the cook’s breathing zone in the kitchen, which was roughly 0.15-m away from, but on the same horizontal plane as the cook’s nose. In the following discussion, the measured PM2.5 levels from the two instruments are referred to as “exposure concentrations” in the living room and the kitchen, because they precisely reflect the PM2.5 concentrations in the breathing zone. The two photometers were cali brated before the experiments. Calibration details can be found in the Supplementary Materials, Fig. S2. The personal portable fan fixed on a shoulder strap around the cook’s chest, 1.2 m above the floor, was operated at a high speed of 3.5 m/s or at a low speed of 2 m/s, where the airflow from the fan was in a vertical direction, as shown in Fig. S1. The two types of non-powered air-purifying particle respirator, KN95 and
2. Methods 2.1. Orthogonal test design As reported in previous studies, the range hood is a conventional tool for re-routing cooking-oil fumes during cooking. Additionally, side panels mounted beneath the hood baffle are used indigenously to block the escape of cooking emissions in traditional houses. Furthermore, the reduction of harmful emissions actually inhaled by occupants at the kitchen countertop while cooking should also be considered. Because face masks are widely used in some construction works to protect from PM2.5 air pollution [33], these devices were considered as a prevention measure in our experiment design. Thus, two types of non-powered air-purifying particle respirators, KN95 (SZ5107; EPC, Beijing, China) and KP95 (EPR HH-10; EPC, Beijing, China), were used. The other two control strategies included carrying a two-speed personal portable fan at the breathing zone when cooking and the activation of an air cleaner having a two-shift operation mode (i.e., high and low speeds) to remove the dispersed cooking-emitted PM2.5 from the living room. For the post-cooking period, when the stove was deactivated after cooking completion, the range hood or air cleaner was either deactivated (duration ¼ 0 min) or left on for an additional period (5–10 min at high speed) with the kitchen door open, to investigate the effect on the PM2.5 levels in the living room. Thus, an L18 (2 � 37) orthogonal experiment, which can efficiently handle multifactor experiments by adopting a minimum number of tests, was performed to obtain the optimal ar rangements for all interventions designed to effectively lower PM2.5 exposure in the kitchen and living room. The schemes of the orthogonal experiment are listed in Table 1. In our experimental design, the in terventions were separated into two parts: one for the cooking period
Fig. 1. Diagram of the testing room and the location of sampling points (unit: cm). 3
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KP95 (specialized for preventing oil particles), were connected to the AM510 air inlet through a 30-cm-long antistatic silicone tube inserted with a sample probe (8025-N95; TSI Inc., Shoreview, MN, USA) to obtain PM2.5 exposure concentrations. A household air cleaner was placed approximately 0.5 m from the measuring point on the floor of the living room. The clean air delivery rates were found to be 18 and 268 m3/h (a clean air exchange rate of ~5 h 1) for low and high air volumes, respectively. An average of 6 tests per day were completed with a time interval of at least 3 days before the next test day. The protocol for each cooking test was as follows. First, the background PM2.5 levels were measured for 15 min before cooking was initiated; the range hood was operated at the designed fan speed settings (i.e., off, low speed, or high speed) for the subsequent cooking stage. To obtain the exact PM2.5 emissions caused by cooking when analyzing the measurement data, the PM2.5 contribution of the make-up air entering the test rooms was eliminated by subtracting the background PM2.5 concentrations. Then, the cooking activity (i.e., frying of mutton with shallots for 3.8 min) was conducted under the designed test conditions with interventions detailed in the orthogonal table. After the stove was deactivated following cooking completion, the range hood or air cleaner was either deactivated or left on for an addi tional duration as described in the orthogonal test design. The PM2.5 concentrations were sequentially monitored during cooking and for 10 min after the cooking period. Between each experiment, the kitchen was forcibly ventilated for at least 45 min by operating the range hood and opening all the windows to ensure that the PM2.5 concentration returned to the background level. The air exchange rate (AER) for each ventilation pattern was also determined via the CO2-decay method, where the baseline concentrations before and after each measurement were averaged. The AERs of the kitchen with the kitchen door open and closed were 3.11 � 0.53 and 1.74 � 0.15 h 1, respectively.
returned to the background level between each experiment. All windows and interior doors, excluding the kitchen door, were closed during the tests to minimize air exchange in the house, aside from that generated by the exhaust hood. 3. Results 3.1. Control effect of intervention measures 3.1.1. Kitchen Fig. 2 shows that, among the controls, the range hood provided the most protection, reducing exposure concentrations by a factor of ~10 for otherwise similar conditions. The use of a mask appears to have reduced concentrations by a factor of 3–5. The reduction in the average PM2.5 exposure concentrations in the kitchen during the cooking period was mainly attributed to range-hood operation and respirator use. These measures appear to be the most effective methods of handling PM2.5 exposure. The fan had a relatively small effect: on the order of 10% or less. More specific results are shown in Tables S4 and S5 of the Sup plementary Materials. The results varied from 0.017 to 2.176 mg/m3 with different interventions, where a combination of wearing a mask and operating both the range hood and the portable fan at high speed was proven to be the most efficient measure for reducing PM2.5 expo sure. The average PM2.5 exposure concentrations with a range hood and respirator employed separately were approximately 200 and 400 μg/m3, respectively. The exposure concentrations dropped significantly with the use of the range hood, and a decreasing trend was observed when an air-purifying particle respirator was equipped for both masks evaluated in this study. However, the effect of wearing a respirator was less remarkable that of range-hood operation, which could possibly be attributed to the lower-measured respirator efficiencies (88% for KN and 92% for KP, as shown in Fig. 3) compared to the nominal efficiency (95%). Additionally, application of a portable fan in the vicinity of the breathing zone likely decreased the exposure levels in general, espe cially when the range hood was kept off.
2.3. Quality assurance and control The same dish of fried mutton with shallots chosen for all cooking tests was cooked by a professional chef, who used the same cooking utensils and followed an identical cooking procedure in each case (Table S2 in the Supplementary Materials) with a stopwatch to ensure repeatability. The dish, which involved 360 g of food ingredients, is suitable for families of 3–4 persons, and was suggested by our profes sional chef to provide a common cooking scenario for most Chinese residences. It was also selected as a typical Chinese dish based on an online survey of 309 Chinese families conducted by Chen et al. [6] (specific results can be found in Table S3). For each test, the food in gredients were weighed in advance on an electronic scale having an accuracy of 0.001 g. All food ingredients were placed within reach to reduce the movements of the cook, and the timekeeper inside the kitchen during the measurement stood away from the cooktop, almost motionlessly. Thus, the movement of the occupants can be neglected. Each room in the flat was equipped with heating radiators, and the temperatures varied within a narrow range of 20.2–22.5 � C. The relative humidity in the kitchen changed from 32 to 46% during the experiment period (Fig. S3). Each set of designed conditions (the 18 open-door cases and 6 closed-door cases) was repeated twice for a total of 48 cooking tests. The relative deviation of the repeated experiments ranged from 1 to 20%, as shown in the Supplementary Materials (Fig. S4). Addition ally, the two AM510 photometers were calibrated before testing, and a set of comparisons between the two instrument readings, ranging from 0.4 to 3.2 mg/m3, was performed for concentration measurement. The relative correlation for the concentration curve between the 2 a.m.510 photometers was higher than 0.98 (R2 ¼ 0.981). Before the experiments, the exposure concentrations for the cook wearing a mask were moni tored. During the test, the cook adjusted the mask to perfectly attach onto his face until the AM510 readings yielded 0 μg/m3, indicating that the mask was sufficiently sealed in consideration of data validity. The kitchen was force-ventilated to ensure that the PM2.5 concentration
3.1.2. Living room Regarding the living room, the average concentrations during entire period of cooking and post-cooking were 0.282–1.187 mg/m3 with the range hood off during cooking, roughly 20 times those when the range hood was running (0.010–0.068 mg/m3). The increase of PM2.5 con centrations during cooking generally rose ~3 min after cooking started. Recall that the entire cooking period was 3.8 min. This addresses the time lapse for PM2.5 pervasion. As shown in Fig. S5, the PM2.5 concen tration in the living room continued to increase for approximately 3–4 min after cooking was finished, and then decayed with time. How ever, on condition that the range hood was running during cooking time, the PM2.5 levels in the living room tended to be stable before the mea surement for post-cooking period ended. Notably, the PM2.5 concen trations can exceed 1.700 mg/m3 if no intervention is performed, as shown in Fig. 4. It was quite apparent that, during the cooking period, the air quality in the living room seldom was affected when the range hood was running. The results shown in Fig. 4 for the living room show that range hood operation was the most effective intervention by far, reducing peak concentrations by a factor of 50–100. With the hood off, operating the air cleaner on high appears to have ~22% effect. Simi larly, the results in Fig. 5 indicate that using a range hood during cooking, irrespective of the speed setting, which contributed ~95% benefit, was much more effective compared to post-cooking in terventions (namely the range hood or air cleaner was left running for an additional period of 5–10 min). By contrast, a decrease of 50%–75% was observed with the application of these post-cooking interventions. The average PM2.5 concentrations in the living room during the entire period ranged from 0.250 to 0.650 mg/m3, indicating that an air cleaner with a clean air exchange rate of ~5 h 1 was not enough to remove cooking emissions effectively. There was a downward trend as the running 4
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Fig. 2. PM2.5 exposure concentration in kitchen during cooking with kitchen-door open (FO: portable fan off; FL: portable fan on at low speed; FH: portable fan on at high speed; RO: respirator off; KN: KN95 respirator; KP: KP95 respirator; HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed).
corresponding reductions were slightly lower when a respirator was worn (80% for KN95 and 83% for KP95). Moreover, the PM2.5 exposure for the cook was reduced by up to 98% when both interventions were applied simultaneously. The removal efficiency of the range hood in this study was determined to be consistent with the results of Poon et al. [34] (87–92%), but much higher than that reported by Chen et al. [6] (52–63%), despite the fact that a higher exhaust rate was used in their experiments (233 m3/h). The PM2.5 concentration distribution in the kitchen was non-uniform when the range hood was kept off. However, in the study by Chen et al. [6], two fans were used to ensure proper mixing of air. Thus, the exposure concentrations obtained with no in terventions, which were considered a benchmark in the reduction cal culations, could be elevated to a higher level. This behavior could likely explain the higher reduction measured in that study. Furthermore, the average exposure concentrations in the open-door cases were generally 10% lower than those of closed-door cases (Fig. S8 of the Supplementary Materials). This is consistent with the findings in the study of Zhou et al. [35].
Fig. 3. Filter efficiency of the two types of non-powered air-purifying particle respirators.
3.2. Significance analysis of interventions Range-hood operation and respirator user were statistically signifi cant interventions affecting the PM2.5 exposure concentrations, compared to the results obtained using a portable fan or by configuring the range hood with side panels (Fig. 6). The range of influence on the air distribution created by the portable fan was relatively smaller than that with the range hood. Moreover, the average PM2.5 exposure for the cook registered an approximate 13% reduction when employing the portable fan at high speeds. However, it was not statistically significant. The reductions observed when the kitchen door was kept open while cooking were statistically significant. Operating the range hood at a high or low speed while wearing a KP95 respirator contributed to effective PM2.5 exposure reduction with a significant difference level of 0.01, in contrast to the significance at a level of 0.05 achieved when wearing a KN95 respirator. No significant difference was observed between the results measured with high- and low-speed settings for the range hood in this study. This is likely due to their similar exhaust rates (123 and 84 m3/h for high and low speeds, respectively, with a relative error <6.4%).
duration of the air cleaner or the range hood increased if the range hood was not used when cooking. The average concentrations in the living room were 7.4% those in the kitchen when the range hood was operated continuously, and 29% those in the kitchen if the range hood was deactivated. Moreover, configuring the side panels for the range hood may have slightly reduced the PM2.5 concentrations in the living room when the range hood remained off during the cooking period (see Fig. 4) Although the average PM2.5 concentrations in the living room were much lower than those of the kitchen during the cooking period, a sta tistically significant increase of 2–20 times was observed during the post-cooking period compared to the cooking period, as shown in Fig. S6. These findings indicate that the PM2.5 emissions remaining in the kitchen could subsequently diffuse into the living room, even with continuous operation of the range hood after cooking, demonstrating that one can abate PM2.5 pollution in the living room by closing the kitchen door immediately after the cooking activities are complete. 3.1.3. Reduction percentage As shown in Supplementary Materials, Fig. S7, the average exposure concentrations could be reduced by 90 and 93% (mean values) using a range hood at low and high flow rates, respectively. However, the 5
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Fig. 4. Peak concentrations of PM2.5 in the living room during cooking (0 cm: the height of the two side panels is 0 cm; 12 cm: the height is 12 cm; 24 cm: the height is 24 cm; ACO: air cleaner off; ACL: air cleaner on at low speed; ACH: air cleaner on at high speed; HO: range hood off; HL: range hood on at low speed; HH: range hood on at high speed).
Fig. 5. Average concentrations of PM2.5 in the living room during entire period of cooking and post-cooking (0 cm: the height of the two side panels is 0 cm; 12 cm: the height is 12 cm; 24 cm: the height is 24 cm; AC duration: air cleaner running duration; Range hood duration: the running duration of range hood).
4. Discussion
closing the kitchen door after cooking to restrain the subsequent dispersion of PM2.5 into the adjacent room, rather than leaving the range hood on, is overall more effective and energy-saving.
4.1. Recommendations to reduce exposure to PM2.5 from cooking The results demonstrate that a low hood-flow rate can be partially compensated by wearing a respirator during cooking, which is costeffective and avoids the inconvenience of ventilation retrofits. Thus, range hood operation at a relatively low flow rate during cooking could be considered sufficient for reducing the cook’s exposure to PM2.5 to an acceptable level, provided a respirator is used simultaneously. Given the discomfort of wearing a respirator, we believe that it should serve as an auxiliary means of partially compensating for low flow rates for resi dents who do not perform retrofit works, such as with the configuration of a new range hood with a sufficiently high flow rate or removal effi ciency. Meanwhile, PM2.5 concentrations in the kitchen can be reduced by keeping the kitchen door open when cooking. The adverse effects in the adjacent room can be reduced by using a range hood. Nonetheless,
4.2. Limitations and prospective research The present study has several limitations. The cooking activity con ducted in this study lasted for a short time of 3.8 min and was composed of only one typical dish, in consideration of the fact that a more complex cooking procedure could add to uncertainty of the experiment results. However, the representativeness of the chosen dish was ensured based on an online survey about cooking behaviors of Chinese residents (Tables S3–(a)-(e)). Besides, only a limited post-cooking period of 10 min was taken into account in this study. However, it was supposed as a reasonable course of action, considering that most Chinese residents would leave the range hood running no more than 15 min according to our previous survey as shown in Tables S3–(e), which was also 6
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Fig. 6. Control effect comparison based on statistical significance analysis (average PM2.5 exposure concentrations in the kitchen during cooking were applied).
consistent with the study of Dobbin et al. [22]. This study focused on interventions free of reconstruction work in existing buildings. Nevertheless, further studies on various ventilation systems are of significance for ventilation design in the pre-construction stages of new buildings, because this is an effective means of improving indoor air quality [36]. Further efforts to enhance extraction-hood ef ficiency are also essential, because respirator wearing may be uncom fortable. Furthermore, the uncertainties concerning some experimental variables (e.g., cooking type and the range hood flow rate) should be considered in future investigations.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by grants from the National Key Research and Development Program of China [grant number 2017YFC0702700] and the Innovative Research Groups of the National Natural Science Foundation of China [grant number 51521005].
5. Conclusions
Appendix A. Supplementary data
In this study, PM2.5 exposure concentrations caused to cooking ac tivities were measured to investigate the utility of multiple interventions based on an orthogonal design. The average PM2.5 exposure concen trations during cooking ranged from 0.017 to 0.473 mg/m3 with a range hood or respirators employed. The results indicated that running the range hood and wearing respirators during cooking decreased the inhalation exposure to PM2.5 in a statistically significant manner, where the reduction percentage was 90–95% and 79–84%, respectively. By contrast, the effect of using a portable fan or configuring side panels for the range hood did not reach statistical significance. Moreover, a scarce increase of PM2.5 concentrations in the living room during a cooking period of 3.8 min occurred when running the range hood with the kitchen door open, which could then be elevated to a much higher level during a post-cooking period of 10 min. The average PM2.5 levels in the adjacent living room could be lowered by 50%–75% with an additional period of 5–10min running the range hood or the air cleaner. In com parison, it would make an improvement of more than 95% if the range hood was remained on during cooking time. These findings provide helpful recommendations to Chinese residents to protect from cookingrelated PM2.5 exposure via low-cost interventions and appropriate cooking behaviors.
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Notes The authors declare no competing financial interest. Competing financial interests The authors have declared that they have no actual or potential competing financial interests. 7
Y. Zhao and B. Zhao
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