Biomass Cookstoves Research Articles

Application of multi-response robust parameter design for performance optimization of a hybrid draft biomass cook stove

A novel design of a hybrid draft biomass cook stove was proposed, constructed and tested for 54 combinations of five important parameters viz. Inlet area ratio, Fuel surface to volume ratio, Pot diameter, Secondary air flow rate, and Pot gap. The combined effects of these factors on the stove performance parameters such as overall efficiency (ηo), CO emissions and PM2.5 emissions were estimated. The data obtained by executing designed experiments (CCD) on the stove prototype was fitted to independent second-order models using RSM. The fitted models were further used to predict the stove performance for different combinations of the five factors. The analysis revealed that the prototype cannot achieve energy performance better than Tier 2 level and ηo greater than 30%. However, the hybrid draft enabled the prototype to achieve Tier 4 level performance in CO and PM2.5 emissions. Desirability function coupled with the fitted RSM models was used for robust parameter optimization of the stove performance to maximize efficiency, minimize emissions and propagation of error. The robust parameter optimization resulted in the best possible overall stove performance of ηo = 26.54%, CO/MJd = 2.249 g/MJ and PM/MJd = 34.67 mg/MJd obtained at the control factor levels of Ms = 1.74 g/s and Pg = 14 mm.

Quantifying the air quality, climate and equity implications of India's household energy transition

Economic growth, urbanization and changes in lifestyles are leading to a transition from traditional fuels to liquefied petroleum gas (LPG) and electricity in Indian households. We use National Sample Survey data – 43rd (1987–88) and 68th (2011−12) rounds – to show that contrary to concerns about rising greenhouse gas (GHG) emissions from fossil-fuel use, switching to LPG and electricity provides health and climate benefits, if non-Kyoto emissions are considered. Our modelled household energy transition scenarios (2011–2030) show that: one, adoption of LPG by 2030 in Business-As-Usual (BAU) projections results in 80% of urban India meeting the World Health Organization's (WHO) indoor PM 2.5 guidelines. In rural households, persistent use of firewood does not significantly improve indoor air quality across the income spectrum. Two, BAU scenario projects only a 3% rise in rural GHG emissions by 2030, driven by a transition away from kerosene lighting in spite of rising electricity consumption. Three, a complete transition to LPG and electricity by 2030 reduces PM 2.5 exposure to below WHO guidelines across all urban and rural households. This is not achieved in the other partial transition scenarios. Four, across scenarios improving coal-based power plant efficiency to 40% and increasing renewables' share to 40% lead to a decrease of 14–18% in GHG emissions by 2030 relative to 2011. Finally, improved biomass cookstoves can reduce indoor exposure by 75–86% but not below the WHO guideline, and result in higher GHG emissions compared to LPG replacement due to non-Kyoto emissions from burning firewood.

Development of a practical evaluation approach of a typical biomass cookstove

Abstract Exposure to air pollutant emissions from household combustion of solid fuels is leading risk factor for premature deaths in the developing countries. A natural draft Improved Cook Stove (ICS) was designed for household combustion of solid fuels. The objectives of the design included multi fuel usage, user friendliness, lower emissions and better efficiency. Comparisons of newly designed cookstove (ND) with Traditional cookstove (TCS) and three other ICS have been discussed. The performance of the ND when loaded with five different solid fuels has also been discussed. Modified Water Boiling Test (WBT) and Bureau of Indian Standards (BIS, 2013) methodology was used for performance evaluation of the designed ICS. The cookstove was designed for 2kW energy output and fuel consumption rate of 1.5 kg/hr. Turn down ratio of 3.23, fire power of 7kW and specific fuel consumption of 85 g/liter was estimated from the WBT. The ND performed better than TCS and other commercial ICS with 75% reduction in PM2.5 and 63% reduction in CO concentrations respectively. The thermal efficiency of ND indicated a significant increase of 106% from TCS. Outcomes from this study can be used for designing a multi fuel biomass stove with enhanced efficiency and lowered emissions.

Cookstove Smoke Impact on Ambient Air Quality and Probable Consequences for Human Health in Rural Locations of Southern Nepal.

Residential emission from traditional biomass cookstoves is a major source of indoor and outdoor air pollution in developing countries. However, exact quantification of the contribution of biomass cookstove emissions to outdoor air is still lacking. In order to address this gap, we designed a field study to estimate the emission factors of PM2.5 (particulate matter of less than 2.5 µ diameter) and BC (black carbon) indoors, from cookstove smoke using biomass fuel and with smoke escaping outdoors from the roof of the house. The field study was conducted in four randomly selected households in two rural locations of southern Nepal during April 2017. In addition, real-time measurement of ambient PM2.5 was performed for 20 days during the campaign in those two rural sites and one background location to quantify the contribution of cooking-related emissions to the ambient PM2.5. Emission factor estimates indicate that 66% of PM2.5 and 80% of BC emissions from biomass cookstoves directly escape into ambient air. During the cooking period, ambient PM2.5 concentrations in the rural sites were observed to be 37% higher than in the nearby background location. Based on the World Health Organization (WHO)’s AirQ+ model simulation, this 37% rise in ambient PM2.5 during cooking hours can lead to approximately 82 cases of annual premature deaths among the rural population of Chitwan district.

The Effect of Inlet Area Ratio on the Performance of Multi-pot Natural Draft Biomass Cookstove

The performance of cookstove is mostly determined by trial-and-error experiments and its evaluation using simple thermodynamics and heat transfer equations. The effect of variation in inlet area ratio on the flame temperature and the exhaust is investigated on natural-type biomass cookstove. Numerical simulations have also been carried out and validated with the experimental results. Commercially available software ANSYS ver. 16.2 is used to simulate the two-dimensional computational domain. The computational domain has been simulated using non-premixed combustion and standard k-e turbulence model. Geometry creation and meshing of the domain are done using ICEM ver. 16.2. Probability density function (PDF) accounts for the interaction between turbulence and fuel composition. The data obtained from the experiment is used as a boundary condition for the numerical simulation. Results showed that CFD is a great tool with accuracy and time-saving features to understand the thermal behavior of cookstove and can be used to model different stoves at different conditions without performing the actual experiment. The value of critical inlet area ratio remains almost the same for any natural draft biomass cookstove, which is around 0.7.

Kitchen concentrations of fine particulate matter and particle number concentration in households using biomass cookstoves in rural Honduras

Cooking and heating with solid fuels results in high levels of household air pollutants, including particulate matter (PM); however, limited data exist for size fractions smaller than PM2.5 (diameter less than 2.5 μm). We collected 24-h time-resolved measurements of PM2.5 (n = 27) and particle number concentrations (PNC, average diameter 10–700 nm) (n = 44; 24 with paired PM2.5 and PNC) in homes with wood-burning traditional and Justa (i.e., with an engineered combustion chamber and chimney) cookstoves in rural Honduras.The median 24-h PM2.5 concentration (n = 27) was 79 μg/m3 (interquartile range [IQR]: 44–174 μg/m3); traditional (n = 15): 130 μg/m3 (IQR: 48–250 μg/m3); Justa (n = 12): 66 μg/m3 (IQR: 44–97 μg/m3). The median 24-h PNC (n = 44) was 8.5 × 104 particles (pt)/cm3 (IQR: 3.8 × 104–1.8 × 105 pt/cm3); traditional (n = 27): 1.3 × 105 pt/cm3 (IQR: 3.3 × 104–2.0 × 105 pt/cm3); Justa (n = 17): 6.3 × 104 pt/cm3 (IQR: 4.0 × 104–1.2 × 105 pt/cm3). The 24-h average PM2.5 and particle number concentrations were correlated for the full sample of cookstoves (n = 24, Spearman ρ: 0.83); correlations between PM2.5 and PNC were higher in traditional stove kitchens (n = 12, ρ: 0.93) than in Justa stove kitchens (n = 12, ρ: 0.67). The 24-h average concentrations of PM2.5 and PNC were also correlated with the maximum average concentrations during shorter-term averaging windows of one-, five-, 15-, and 60-min, respectively (Spearman ρ: PM2.5 [0.65, 0.85, 0.82, 0.71], PNC [0.74, 0.86, 0.88, 0.86]).Given the moderate correlations observed between 24-h PM2.5 and PNC and between 24-h and the shorter-term averaging windows within size fractions, investigators may need to consider cost-effectiveness and information gained by measuring both size fractions for the study objective. Further evaluations of other stove and fuel combinations are needed.

Scenario analysis for promoting clean cooking in Sub-Saharan Africa: Costs and benefits

Nearly 900 million people in Sub-Saharan Africa rely on traditional biomass for cooking, with negative impacts on health, biodiversity and the climate. In this study, we use the IMAGE modellingframework to construct two sets of scenarios for promoting clean cooking solutions. In the first set, specific policy options to promote clean cooking are evaluated, while in the second the SDG target to achieve universal access to modern cooking energy by 2030 is imposed. The study adds knowledge to understanding the impact of individual policy options on access to clean cooking solutions, and provides insight into synergies and trade-offs of achieving the SDG targets on human health, biodiversity and climate change. The results show that, in the absence of coordinated actions, enabling policies and scaled-up finance, the number of people in Sub-Saharan Africa relying on traditional biomass cookstoves could amount to 660–820 million by 2030. Subsidies on specific clean cooking technologies or fuels could increase their use substantially, but could hinder the uptake of alternative clean cooking fuels or technologies. Meeting the SDG target has considerable social, environmental and economic benefits, and could even lead to lower total fuel expenditures. However, investments in cookstoves need to be quadrupled relative to baseline.

Successes and Challenges of Improved Biomass Cooking Stoves Adoption along the Product Value Chain in Kilimanjaro Region, Tanzania

The aim of this study was to assess the adoption of ICS along the value chain. The existing studies have focused much on measuring adoption based on the user’s installation or purchase of the ICS and few have gone to the level of assessing other aspects along the ICS value chain. The argument of this paper is that adoption is a multidimensional concept that goes beyond the initial acquisition of the stove to the sustained use of the same. Using a cross-sectional study design data were collected from 294 households in two Districts of Kilimanjaro regions and were analyzed using both quantitative and qualitative approaches. The findings show that at the lower levels of value chain i.e. promotion and distributions the efforts have been somehow successful since people are aware of ICS benefits and negative effects of using traditional fuels and stoves. In addition, various stove distributors and technicians are in place. On the other hand, the uptake is limited since only 26% of all households had ICS in place of which only 22.1% had functional stoves. The intensity of ICS use is very limited and households have not integrated the stove into household cooking behavior. The study concludes that the stoves program implementers have adopted a disintegrated approach that disconnects various levels of the value chain. The efforts are much concentrated at lowers levels with limited interventions to address challenges limiting uptake, the intensity of use and sustained adoption. The study recommends that a holistic and integrated approach that will facilitate ICS adoption along the value chain should be adopted. This approach will facilitate forward and backward communications on challenges facing each level of the value chain.

Predicting and analyzing the performance of biomass-burning natural draft rocket cookstoves using computational fluid dynamics

Nearly three billion people in the world today rely on biomass for their cooking needs. Indoor cooking using biomass has been identified as a major cause of respiratory illnesses, resulting in four million premature deaths every year. Improved biomass cookstoves may help mitigate this challenge. This paper presents a two-dimensional axisymmetric steady-state computational fluid dynamics (CFD) model of a biomass burning, natural draft rocket cookstove. The CFD model includes coupled sub-models representing combustion, turbulence, and heat transfer. The model is validated against experimental data and used to predict temperatures and flow inside the cookstove, including the airflow rate through the cookstove and heat transfer to the cookpot. We find that the excess air is typically many times stoichiometric air during standard operating conditions and is sensitive to flow field obstructions. We analyze the effects of geometric and operational features such as the pot support height, secondary air entrainment, cone-deck shape, and baffle placement within the cookstove on the flow, airflow rate, mixing, and stove thermal efficiency. The model shows that secondary air entrainment, though ineffective by itself, increases turbulent mixing when used in conjunction with a central baffle but reduces thermal efficiencies due to enhanced heat transfer to the walls. We find that a lower pot support height decreases the airflow rate and increases thermal efficiency. We model thirty-six cone-deck configurations and find that the cone-deck shape primarily affects the airflow rate through the stove, with more constricted designs leading to higher thermal efficiencies.

Feasibility study of TEG-integrated biomass cook stove for electrical power generation specific to rural areas with inadequate electricity

ABSTRACT Access to standard form of energy in cooking and lighting has been a serious concern among most of the people residing in rural parts of the world. More than 2 billion people concentrated mostly in rural areas of India and sub-Saharan Africa use firewood in inefficient (thermal efficiency is <8–10%) traditional cook stoves. Around 15% of input energy from fuel is stored within the stove body as waste heat. Further, the annual per capita electricity consumption is just over 1000 kWh compared to world average of more than 3000 kWh. Whereas, the figure drops to 314 kWh in the northeastern state of Assam, India. Thermoelectric generator (TEG) can be used to recover the waste heat and utilize it in the conversion into electricity on the principle of Seebeck effect. This research work is attempted to test the feasibility of integrating a TEG module with an Ministry of New and Renewable energy (MNRE)-approved improved clay made cook stove named Sukhad using fundamental heat transfer and thermoelectric equations. Preliminary tests of the TEG-integrated cook stove showed a potential of generating 2.7 W of electrical power and illuminating a 3 W LED bulb.

The Ghana Randomized Air Pollution and Health Study (GRAPHS): a cluster randomized trial of Liquified petroleum gas (LPG) and efficient biomass cookstoves delivered during pregnancy

OPS 33: Health impact of interventions 2, Room 411, Floor 4, August 28, 2019, 10:30 AM - 12:00 PM Background/Aim: Household air pollution from inefficient biomass cookstoves causes millions of avoidable deaths annually. We urgently need reliable information on potential interventions. The Ghana Randomized Air Pollution and Health Study (GRAPHS) was a cluster randomized trial assessing the effect of a cookstove intervention delivered during the first two trimesters of pregnancy on birth weight and on physician-assessed pneumonia during the first year of life. Methods: We recruited pregnant women in Kintampo North and South districts in Ghana prior to 24 weeks gestation, as determined via ultrasound performed by trained midwife, and assigned them to one of three study arms. In control arm communities, study participants continued to cook with traditional cookstoves. In LPG communities, households received one two-burner LPG cookstove and free LPG. In efficient biomass cookstove communities, households received two fan-assisted improved biomass-burning stoves. Control and efficient cookstove participants received LPG stoves at the end of the trial. Birth weight was assessed by study staff stationed in birth clinics, or, in the case of home births, by home visit within 24 hours of delivery; in both settings, birth weights were measured using calibrated digital scales. Trained field staff visited study children weekly during the first year of life, and referred all community-assessed respiratory illnesses to a study physician, who assessed pneumonia status using the WHO Integrated Management of Childhood Illness (IMCI) guidelines. Results: We enrolled 1414 non-smoking, pregnant women resulting in 1303 live births. 1122 infants completed follow-up through the first year of life, with 54,768 child-weeks of fieldworker surveillance. Our intention to treat analysis showed no significant difference in birth weight or physician-assessed IMCI pneumonia in either of the intervention arms. Conclusions: Neither intervention reduced pneumonia risk or increased birth weight. Future intervention studies should consider community-level energy system transitions.

Exposure misclassification from area sampling in epidemiologic studies of cookstove emissions

TPS 722: Low and middle income countries: indoor air pollutants, Exhibition Hall, Ground floor, August 28, 2019, 3:00 PM - 4:30 PM Background/Aim: Measuring personal exposure to cookstove emissions in resource-poor settings is logistically challenging, and kitchen area sampling is commonly used as a proxy for personal exposure. However, little is known about the effectiveness of this approach to accurately classify exposure in epidemiologic studies of cookstove emissions. Methods: We sampled area concentrations and personal exposure to fine particulate matter (PM2.5) and carbon monoxide (CO) among 180 women in a randomized controlled trial of a liquified petroleum gas (LPG) cleaner-cooking intervention in Puno, Peru. PM2.5 and CO were monitored for 48 hours at one-minute intervals and PM2.5 measurements were gravimetrically-adjusted. Using simple linear regression, we assessed the ability of kitchen area measurements to predict personal exposures using the log-transformed mean and 99th percentiles for each pollutant, stratifying between 90 participants using biomass cookstoves and 90 using LPG cookstoves. Results: The adjusted R2 for predicting mean PM2.5 personal exposure given mean PM2.5 kitchen area concentration was 0.17 for biomass-users, 0.05 for LPG-users, and 0.33 for all participants. When predicting 99th percentile PM2.5 personal exposure given 99th percentile PM2.5 kitchen area concentration, the adjusted R2 increased to 0.27 for biomass-users, 0.06 for LPG-users, and 0.45 for all participants. For CO, the adjusted R2 using the means was 0.05 for biomass-users, 0.04 for LPG-users, and 0.25 for all participants. For 99th percentile CO, the adjusted R2 increased to 0.09, 0.12, and 0.30 for biomass, LPG, and all participants, respectively. Conclusions: Kitchen area concentrations are moderately effective at predicting mean personal exposures among a group of both biomass and LPG users, but are poor at predicting personal exposures within a single fuel group. Kitchen area monitors with high-temporal resolution can predict personal exposure to cookstove-related concentration spikes with moderate accuracy, facilitating epidemiologic studies of health outcomes associated with short-term, high-dose exposures.

Adoption of Clean Cook stoves in Rural Ghana

S02: Harmonizing insights from intervention studies, contextual information and resource availability to develop policy advocacy for clean cooking and domestic fuel adoption in Africa, Room 417, Floor 4, August 27, 2019, 10:30 AM - 12:00 PM Background/Aim: Clean cook-stoves reduce exposure to household air pollution and associated health problems, conserve firewood, and save time from firewood gathering and cooking. Despite these benefits, adoption of these stoves is low in many countries. The aim of the study is to help determine the best way to promote the adoption and sustained use of clean cook-stoves in rural Ghana. Methods: Participants for this study were sampled from the Ghana Randomized Air Pollution and Health Study (GRAPHS), which provided participants with BioLite (an improved biomass cook stove) and Liquefied Petroleum Gas (LPG) cook-stoves. Qualitative interviews were conducted to identify the motivators and barriers to the adoption of clean cook-stoves. Quantitatively, stove use and time use surveys were conducted. Behavioral change and LPG delivery models were also implemented to improve adoption of clean cook-stoves in the study area. Results: Participants in the qualitative survey reported that the clean cook-stoves cook faster, emits no or very little smoke, improves their health and promotes harmony in the home. Cost was the main barrier to the adoption of clean cook-stove especially the LPG stoves. LPG participants spent about 19 minutes less time gathering firewood compared to users of the traditional three-stone cook-stoves and about 15 minutes less time compared to users of the Biolite cook-stove. This was significant at a p-value of 0.002. Cooking time per cooking episode was lesser for LPG users compared to the other stove users. Conclusion: Understanding the motivators and barriers to clean cook-stove usage could help promote usage of these stoves. LPG were well liked, and save household time for gathering firewood and also time per cooking episode. Cost remains a critical barrier.

Effects of a cleaner-burning biomass cookstove intervention on augmentation index and central pulse pressure during a randomized controlled trial in rural Honduras

Effects of a cleaner-burning biomass cookstove intervention on augmentation index and central pulse pressure during a randomized controlled trial in rural Honduras

Abstract # 4273 Stocking density during rearing affects the immune system of laying hens

Traditional cooking is today's largest global environmental health risk. Over 640 million people in Africa are expected to rely on biomass for cooking by 2040. In Kenya, cooking inefficiently with wood and charcoal persists as a cause of deforestation and household air pollution. This research analyses the effects of four biomass cookstove strategies on reducing air pollutant emissions in Kisumu County between 2015 and 2035 using the Long-Range Energy Alternatives Planning system. The Business as Usual scenario (BAU) was developed considering the historical trends in household energy use. Energy transition scenarios to Improved Cookstoves (ICS), Pellet Gasifier Stoves (PGS) and Biogas Stoves (BGS) were applied to examine the impact of these systems on energy savings and air pollution mitigation. An integrated scenario (INT) was evaluated as a mix of the ICS, PGS and BGS. The highest energy savings, in relation to the BAU, are achieved in the BGS (30.9%), followed by the INT (23.5%), PGS (19.4%) and ICS (9.2%). The BGS offers the highest reduction in the GHG (37.6%), CH4 (94.3%), NMVOCs (85.0%), CO (97.4%), PM2.5 (64.7%) and BC (48.4%) emissions, and the PGS the highest reduction in the N2O (83.0%) and NOx (90.7%) emissions, in relation to the BAU.

Waste heat recovery from improved cookstove through thermoelectric generator

An improved, family-sized biomass cookstove was designed with a thermoelectric generator (TEG). The main objective of coupling the cookstove to the TEG was to produce electricity by utilising the waste heat emitted from the outer body and grate of the cookstove. A rectangular metal plate of 0.12 × 0.08 m2 was used to hold five TEG modules in series. The plate was coupled with the outer body of the cookstove to collect waste heat from conduction losses. A L-shaped extension strip of length 0.11 m was extended from the metal strip to collect the waste heat from the grate. The power produced from the TEG was used to power a small fan (0.16 A, 12 Volt DC) which supplied primary and secondary air for fuel combustion. The cookstove was tested for power production with a multi-fuel option in the dual draft air supply mode. The average power output from the TEG tested in forced convention mode with Desi babul (Acacia nilotica) wood and Groundnut (Arachis hypogaea) shell pellet was 2.3 and 2.6 W, respectively. It was observed that the produced power was enough to operate the fan in forced draft air supply mode.

Computational Fluid Dynamics Study of Biomass Cook Stove—Part 1: Hydrodynamics and Homogeneous Combustion

In this work, a computational fluid dynamics (CFD)-assisted optimization study has been carried out, implementing geometric design modifications in a biomass cook stove (BCS) to achieve uniform air...

Experimental and numerical analyses for designing two-pot biomass cookstove

The use of cookstoves is as old as human civilization, and food cooking is considered to be one of the major steps responsible for human brain development. Around 60% of the world population still relies on the use of biomass cookstoves for cooking and heating needs. The present work is an attempt to find a better and easy solution for designing a cookstove. A mathematical approach is presented in the paper to determine the performance of a cookstove to reduce the trial and error method of experimentation. The mathematical model is verified and validated with the experimental results. Three sets of water boiling test are performed to measure the cookstove performance. The average deviation in the model predicted and the experimental values for mass flow rate, temperature and thermal efficiency is 4.4%, 9%, and 7%, respectively. To determine the exhaust values, the mathematical outputs are set as the computational model input and the values of temperature, exhaust and flow structures are determined. The exhaust values of the computational model are in good agreement with the experimental results.

A mathematical modeling of two-pot biomass cookstove

Biofuels are extensively used as primary fuel in cookstoves by the rural masses in India. About 70% of the population resides in the rural area, out of which 70% are entirely dependent on biofuels for their energy requirements. The traditional cookstoves are poorly designed causing inefficient burning. Hence, the efforts are needed to improve the quality of these cookstoves concerning of design and efficiency. The present work overcomes the difficulty of designing the two-pot biomass cookstove by presenting a simple mathematical approach to evaluate the thermal performance using the heat and mass transfer equations. The model predicts the heat interaction between the stove body and pots, combustion temperatures in different zones, the thermal efficiency and excess air ratio for different geometrical parameters of the stove. The model values are validated with the experimental results and found to be in close agreement. The findings of the model are likely to change the future cookstove modeling and design approach.

A follow-up study after an improved cookstove intervention in rural Mexico: Estimation of household energy use and chronic PM2.5 exposure

The benefits of improved biomass cookstoves (ICS) depends on their adoption and sustained use. Few studies have documented if and how they are used more than five years after being introduced.We conducted a 9-year prospective cohort study among young rural women in the highlands of Michoacan, Mexico. Participants had received a Patsari ICS during a community trial either in 2005 or 2006. With retrospective information collected in 2012–13, we studied the households' energy use, ICS survival, and cooking practices during the follow-up period. Using an exposure model constructed with personal PM2.5 measurements in a subsample of homes at the time of the initial trial in 2005, we estimated the exposure associated with different energy use patterns during the follow-up period.The ICS had a mean lifespan of 4 years, after which more than half of the stoves were not in use; therefore, the use of open fire increased, particularly among the indigenous communities. ICS use peak was achieved two years after the initial trial, either exclusively or combined with open fire. Yearly household energy use and other variables were used to estimate chronic air pollution exposure. Mean PM2.5 exposure during the follow-up period ranged from 51 to 319 μg/m3; the median was 102 and 146 μg/m3 for mainly ICS and mainly open fire use, respectively.The ICS has a useful period after which it needs maintenance, repair, or replacement. Unfortunately, many programs have not afforded a follow-up component. Exposure to biomass smoke air pollutants can be reduced by using an ICS instead of the traditional open fire. Household energy strategies should ensure equitable access to clean energy options adapted to local needs and preferences with culturally appropriate technology implemented on a sustainable perspective.