Perceived air quality (PAQ) assessment methods in office buildings: A systematic review towards an indoor smellscape approach

Indoor air quality (IAQ) has significant impacts on office occupants ’ productivity, well-being and health. Addressing IAQ not only means ensuring that contaminants are below harmful concentration but also that people exposed are satisfied. However, current standards often lack clear metrics and thresholds dedicated to Perceived Air Quality (PAQ). Therefore, it is important to examine whether there is a prevalent method in the literature that could lead towards standardization. This review study constitutes the first comprehensive critical exploration of the subject. Adopting the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, the objective is to synthesize and compare diverse methods (subjective vs instrumental evaluations; object of judgment; component of perception; rating scales) for assessing PAQ in office buildings, based on insights from 93 field and laboratory studies. Results show that the assessment of PAQ predominantly relies on questionnaires (90 %), with a very smaller percentage using alternative methods such as olfactory indices, diaries, interviews, sensory testing, and text mining techniques. Workers ’ satisfaction is the most commonly evaluated aspect in PAQ questionnaires, often measured on a 7-point Likert scale. Odours are typically characterized in terms of intensity by utilizing a continuous 6-point unidirectional scale. Olfactory stimuli are usually considered with a negative connotation


Introduction
Since the 1980s, there has been a growing interest in the impact of indoor air quality (IAQ) on well-being, productivity, and health [1].This is particularly true today as buildings are constructed with increased airtightness for reasons of energy efficiency.Office buildings are a very sensitive building category as people spend a significant amount of time in them, but as end users, they often have limited control over ventilation and IAQ.
Organizations such as the World Health Organization (WHO) have proposed guidelines for pollutants and thresholds to ensure acceptable IAQ, considering their harmful effects on health [2].Thus, achieving good IAQ goes beyond safeguarding health; it must also create feelings of comfort, pleasure, and enhance productivity.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines Acceptable IAQ the "Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80 % or more) of the people exposed do not express dissatisfaction" [3].On the other hand, Acceptable perceived air quality (PAQ) is defined as the "Air in an occupied space toward which a substantial majority of occupants express no dissatisfaction on the basis of odour and sensory irritation.Acceptable PAQ is necessary, but not sufficient, to meet acceptable IAQ" [4].Furthermore, the concept of odour is introduced in standards as "A quality of gases, liquids, or particles that stimulates the olfactory organ" [3].From these definitions, it is evident that PAQ is a sub-aspect of IAQ, which involves both objective requirements (concentration of contaminants) and subjective requirements (i.e., satisfaction in reference to PAQ).On the other hand, the perceptual evaluation of odours is a sub-aspect of PAQ, which is a broader evaluation compared to that of odour because it also covers other aspects, such as possible mucosal irritations (e.g., eyes, throat, nose).
People can assess PAQ based on a feeling of comfort, which can be more precise than instrumental devices [5].This sense of comfort relies on information gathered through various sensory organs, including the nose, throat, eyes, skin, and hypothalamus.The combined response to temperature, humidity, and a wide range of contaminants allows us to perceive the air as either fresh and pleasant or stale, stuffy, and irritating [6].
Assessing IAQ based on human senses is challenging due to various factors.Firstly, there are many different chemicals involved, and some harmful air contaminants might not be sensed at all (for example, carbon monoxide or radon) [7].Even for pollutants that can be detected by their odour or irritation effects, it is necessary to determine who is to judge what is acceptable.This could involve a random sample of occupants, a panel of individuals entering a building, those untrained (i.e., uncalibrated but representative, sometimes called "naïve"), or individuals trained to respond according to consistent criteria.Moreover, the challenge of adaptation should be considered.Indeed, it takes only 3 min for people to become less sensitive to odours present in a room [4].Over longer periods (weeks or months), individuals may come to accept even a harmless odour as normal.Another challenge arises from the interaction of IAQ with other factors.Human responses may stem from IAQ problems, but they can also be influenced by factors independent from IAQ, such as temperature, humidity, draught, lighting, noise, or personal control over the environment [8,9].
To assess PAQ, Standards ISO 16000-30 [10] and ISO 16000-28 [11] introduced the predicted Percentage of Dissatisfied (PD) index, as a percentage ratio of dissatisfied individuals to the total number of the untrained panel of people.However, there is a lack of standardized methods to determine this dissatisfaction percentage.In the following, the PD calculation methods outlined in standards and protocols are introduced.These methods involve both approaches relying on human feedback and methods using proxies such as indices obtained through instrumental measurements.Additionally, chemical and cognitive investigation techniques are presented, which can offer complementary information to objective and subjective evaluations.
Standards such as CEN 1752 [12], ISO 16814 [4] and ISO 17772-1 [13] express the PD as a function of ventilation rates, Olf and Decipol index, and CO 2 concentration.Other standards, like ISO 28802 [14], suggest evaluating PAQ through questionnaires, introducing the intensity, acceptability and satisfaction scales.Subjective evaluation is also recommended by ASHRAE 62.1 and Chartered Institute of Building Services Engineers (CISBE), that defines acceptable PAQ if less than 50 % people perceive odours, less than 20 % feel discomfort, less than 10 % experience mucous irritation, and less than 5 % feel irritable for less than 2 % of the time in enclosed spaces [3,15].Leading building classification and certification protocols like WELL and LEED adopt subjective survey methods, utilizing tools like the CBE (Center for the Built Environment) Occupant Survey [16].Furthermore, there are also methods of chemical and cognitive investigation that can complement subjective measurements of PAQ by adding information on the chemical nature of odours or cognitive insights into the mechanisms underlying the perception of olfactory stimuli depending on the activated part of the brain.Electronic noses can detect and differentiate odours by mimicking the capabilities of a human nose.Conductance sensors can detect odours through changes in electrical conductivity caused by the presence of specific chemical substances in the odours.Brain imaging techniques are used to study brain activity associated with the perception of odours.
Since there are various methods for assessing PAQ, it is important to examine whether there is a prevalent method in the literature that could lead towards future standardization, thereby facilitating the harmonization of methodologies employed in IAQ research and enabling future meta-analyses.Adopting the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [17], this review aims to address the following research questions: (1) How is PAQ assessed in office buildings in the literature?(1.1)To what extent are the metrics used in the literature present in existing standards and protocols?

Methods
A literature review analysis was conducted to investigate the methods of evaluating PAQ as documented in scientific literature, with a focus on office buildings.The literature review adheres to the PRISMA guidelines [17] to ensure a systematic approach to the collection, analysis, and reporting of relevant literature.

Search strategy
A literature search was conducted on the 'Scopus' database in July 2023 to identify studies related to the perception of IAQ ('perceived air quality' OR 'odour*' OR 'smell*' OR 'odour*' OR 'scent*' OR 'indoor environmental quality') specifically in office environments ('office*').The complete research query was formulated as follows: (((('perceived air quality' OR 'odour*' OR 'smell*' OR 'odour*' OR 'scent*' OR 'indoor environmental quality') AND ('office*'))).The decision to use both "perceived air quality"/"indoor environmental quality" and "odour*"/ "odour*"/"smell*"/"scent*" as search keywords aimed to capture a broad range of studies on both general indoor air quality perception (as a G. Torriani et al. subfield of indoor environmental quality research) and specific odour perception research.This approach addresses the lack of consistent terminology in the field, ensuring a comprehensive review by maximizing the inclusion of relevant articles and minimizing the risk of omitting important studies.
The search included papers that focused on PAQ assessments (I1).Articles written in English (I3) after the year 2000 (I4) were considered in their final version (I5), excluding books, book chapters, and conference papers (E1).Field studies conducted in office buildings or laboratory experiments simulating office environments through furnishings and participant activities were included (I2).Papers from distant research areas unrelated to indoor environments (e.g., business, dentistry) were excluded (E2).The inclusion and exclusion criteria are detailed in Table 1.
A total of 1244 documents were retrieved using the specified research query.Some articles were excluded through search filtering based on language (n = 79), year of publication (n = 132), publication stage (n = 9), document type (n = 368), and subject area (n = 117).Titles and abstracts of 483 articles were reviewed, leading to exclusion of articles not focused on offices (n = 157), and not addressing occupants' perception of indoor air quality (n = 207).
A total of 119 articles were assessed for eligibility, and their full text was reviewed.Subsequently, 24 articles were further excluded as not representing field studies or laboratory experiments (n = 10), not addressing occupants' perception of IAQ (n = 14) and as from distant research area (n = 2).Ultimately, the articles included in the review amounted to 93 papers.
Fig. 1 illustrates the selection procedure in accordance with the PRISMA guidelines.

Data extraction and analysis
The data information was manually extracted from the papers, encompassing general article information (e.g., keywords), details on the type of study (i.e., field study or laboratory experiment), the country and the altitude where it was performed, the type of buildings assessed (i.e., year of construction/renovation of the office building, office layout), the monitoring details (i.e., year, season, monitoring duration), and the human sample (i.e., total number of human samples, number of males, number of females, average age).Regarding the assessment methods of PAQ, details were recorded regarding the evaluation approach (e.g., questionnaire, text mining), and in the case of questionnaire evaluations, the type of questionnaire (i.e., one-off or right here-right now), the assessed categories (e.g., air acceptability, odour intensity), and the related scale (e.g., Likert, check-box) and number of points.Additionally, information was gathered to determine if the papers also evaluated the effects of PAQ on health and productivity.
For the completed review table, please refer to Supplementary Material.

Description of the included papers
Ninety-three studies addressing the perception of indoor air quality in offices, published from 2000 to July 2023, have been reviewed.A notable 40 % of these articles were published in the last five years (2019-2023), with a peak in 2020 and 2021, which may be related to the spread of the Covid-19 pandemic and a consequent interest in the subject (Fig. 2).Ninety-eight percent of the studies analyse at least one additional domain besides IAQ, with thermal comfort being the most common, given the established influence of parameters such as air temperature and relative humidity on PAQ [18].However, in recent years, there has been a growing trend towards an approach that simultaneously considers all domains of IEQ (IAQ, thermal comfort, acoustic comfort, visual comfort) (Fig. 2).This could be the effect of milestones review works on multi-domain studies in 2018-2020, also following the activity of international working group (e.g., IEA EBC Annex 79) [19,20].It should be noticed that no study has investigated the relationships of IAQ exclusively with visual comfort or exclusively with acoustic comfort.
Examining studies worldwide, it was found that 19 % were conducted in the United States (North America), 14 % in Denmark (Europe), and 8 % each in China and Singapore (Asia).This highlights a nonuniform distribution of studies across the globe that may lead to findings that are not universally applicable due to perception bias and environmental variability across different countries (Fig. 3).
Two-thirds of the reviewed studies were conducted as field studies, while one-third took place in laboratories simulating office environments.Table 2 illustrates the relative frequencies of information reported in the reviewed papers.
The monitoring duration was less than one week in 57 % of lab studies, whereas it spanned several months in the case of field studies, allowing for a relatively even coverage of all seasons.Studies have been conducted in open-space building types (no partitions, low partitions, high partitions) and enclosed office types (shared, private) with similar relative frequencies in the case of field studies.However, there is a higher frequency of simulation for the enclosed type in lab studies.
Field studies involved more than 100 participants in 65 % of cases, while laboratory studies typically included a range of 11-50 participants in 70 % of cases.Information on the average age of the human sample, when available, indicates a preference for the age range of 18-28 years, especially in lab studies where this occurs in 70 % of cases due to the recruitment of predominantly student participants.
Studies were either gender-balanced or skewed towards either female or male participants, especially when investigating phenomena specific to a particular gender (e.g., Ref. [21]).In this analysis, gender balance is considered achieved if there is a ratio of 50 ± 5 % of men/women.It can be noticed that gender balance was more easily attainable in lab studies where participants were pre-selected.

Table 1
Eligibility criteria used in the selection process of the articles.

Assessment methods of PAQ in office buildings
The assessment of PAQ in the 93 reviewed papers involves both methods relying on human feedback and methods using proxies such as indices obtained through instrumental measurements.Among the former, we find diaries [62,63], interviews [63], sensory testing [23,64], and text mining techniques [65], as well as questionnaires, which are employed in the vast majority of cases [21-23,23,25-36,38-43, 45-50,52-63,63-112].In the second case, indices such as Olf and Decipol [23,66], or the Indoor Air Quality Component Index [68] are utilised.Fig. 4 illustrates the distribution of the assessment methods of PAQ in office buildings while the following paragraphs focus on each method.

Olf and Decipol
Only 2 % of the analysed papers, which were conducted in Denmark in the early 2000s, attempt to investigate IAQ using the Olf and Decipol indices [23,66].
Introduced in 1988 by Fanger [113], the Olf index is used to quantify pollution sources, while the Decipol is employed to measure the concentration of air pollution perceived by humans.An Olf is defined as the emission rate of air pollutants from a standard person (bioeffluents).Any other pollutant source intensity is expressed as an equal source intensity, defined as the number of standard persons (Olf) causing the same dissatisfaction for the actual pollution source.If we dilute a pollutant source with 10 L/s of pure air, the perceived pollutant intensity is defined as 1 Decipol, or 1 Decipol equals 0.1 Olf/(L/s).The Decipol, in particular, is used in literature to quantify the percentage of dissatisfaction related to IAQ, exploiting the relationship between dissatisfaction percentage (PD, %) and perceived air pollution (Decipol, C), using Equations ( 1) and (2) [23,66].When pollution intensity exceeds 31.3Decipols, the IAQ dissatisfaction percentage is deemed absolute dissatisfaction. (1)

Indoor air quality component index I IAQ
Mujan et al. [68] (1 % of the reviewed papers) tried to correlate occupants' satisfaction with the concentrations of indoor air pollutants such as Total Volatile Organic Compounds (TVOC), PM 2.5 , and CO 2 , using the Indoor Air Quality Index (I IAQ ).This index represents the minimum value among satisfaction indices I CO2 , I TVOC , I PM2.5 , respectively calculated by measuring logarithmic concentrations of CO 2 , TVOC, and PM 2.5 according to Equations ( 3)-( 6) [68].Part of a comprehensive index covering all aspects of Indoor Environmental Quality (I IEQ ), the I IAQ demonstrated good agreement with occupants' perception, with a mean absolute error of less than 3 %.

Questionnaire
The vast majority of reviewed papers (90 %) investigate PAQ through the use of questionnaires.
The questionnaire method involves quantifying human responses to an environment using subjective scales on surveys relevant to the psychological or physiological phenomenon of interest [14].
Questionnaires are administered in paper form [46,68,103] or digitally, either as web-based surveys sent via email [50,83,98,102,104,105] or through dedicated smartphone or computer applications [34,52,106], or via an intranet [80].A novel method for collecting feedback is through occupant voting systems (OVS), which allow occupants to express their discomfort using a button with a corresponding colour, positioned at each workstation [114,115].
The investigated studies assess PAQ by examining two different objects of judgment, i.e. general feedback regarding IAQ, and/or specific feedback regarding odours.The second category of questions allows for more detailed responses regarding odours compared to the broader category of questions, of which it is a subgroup.Evaluations encompass different components of experience, which can be categorized into six groups, namely freshness/stuffiness, quality, comfort, acceptability, satisfaction, intensity, and character.The IAQ is most often evaluated in terms of satisfaction, acceptability and freshness/stuffiness. Odours are mainly evaluated in terms of intensity.Fig. 5 illustrates the clustering of reviewed papers involving the questionnaire method according to the object of judgment and the assessed component of perception.
In the case of satisfaction regarding IAQ, PD can be calculated as the percentage ratio of people who gave a score equal to or lower than − 1 to

Table 2
Relative frequencies of information reported in the reviewed papers.N/S = Not specified.IAQ = Indoor Air Quality; TC = Thermal Comfort; AC = Acoustic Comfort; VC = Visual Comfort. the total number of participants [85], or the average score can be calculated, and participants are considered dissatisfied if this average score is equal to or lower than − 2 [91].
In the case of acceptability of PAQ, the mean acceptability ratings can be converted to PD according to the equation by Gunnarsen and Fanger [121]: Where PD = Percentage of dissatisfied with the air quality (%) and Acc = Mean vote of air acceptability.PD can also be calculated as the percentage ratio of people who responded with values between clearly unacceptable and just unacceptable to the total number of respondents [80,82].In some instances, only individuals who stated that PAQ is clearly unacceptable are considered dissatisfied [66,72].The mean acceptability ratings can also be transformed to PD and subsequently into Decipol units, which are used to quantify the PD related to PAQ [23,66].
When assessing PAQ through questionnaires, most studies (59 %) also evaluate other aspects of IEQ like thermal comfort, acoustic comfort, and visual comfort.Additionally, PAQ assessment is often linked with productivity evaluation in 34 % of studies, and with the evaluation of SBS in 36 % of cases.Other questionnaire modules can be used to collect data on office usage (e.g., working hours, occupancy density) and/or respondent characteristics (e.g., demographic information, personal habits).

Diary
2 % of reviewed papers investigate PAQ using diaries.The Diary method entails participants documenting their observations, emotions, or encounters related to PAQ at irregular intervals throughout the day [123].Diaries may be either unstructured or structured, the latter involving predefined questions or scales to gauge perceptions of odours, stuffiness, or other sensory experiences [62].Diaries can also take the form of video recordings over a specific period; every time workers encounter an episode they wish to note, they can document it through these recordings [63].

Interview
1 % of reviewed papers investigate PAQ using interviews.Interviews involve direct conversation between the researcher and participants, offering a platform for in-depth exploration of individual experiences with PAQ.These can be structured (i.e., using predetermined questions with fixed response formats), semi-structured (i.e., using predefined questions with flexibility for follow-up inquiries), or unstructured (i.e., using free-flowing conversation), allowing flexibility in how information is gathered.Gathering direct feedback through interviews has the advantage of further exploring responses, getting in-depth information on participants' experience.Interviews can be combined with sensory tests, such as employing video-taped smell-oriented interviews using paper strips impregnated with "office smells" like coffee, sweat, and office furniture [63].

Text mining
2 % of reviewed papers investigate PAQ using text mining techniques.Text mining involves analysing large volumes of text data to extract relevant information about PAQ.This can include online reviews [65] or responses in POE surveys [69].Using algorithms and natural language processing, researchers can identify patterns, trends, and themes related to air quality perceptions without direct interaction with participants.

Sensory testing
2 % of reviewed papers investigate PAQ using sensory testing.Unlike other subjective techniques such as questionnaires, diaries, interviews or text mining, sensory tests are specifically targeted to find the cause(s) of unpleasant or objectionable odours.Sensory testing is a structured approach where participants (either trained or untrained) assess specific sensory aspects of air quality on site [23,64] or in controlled environments.In the latter case, air is collected from the site and transported to the laboratory in sampling containers where it is presented to human participants using odour presentation instruments, such as olfactometers.The evaluation is point in time, and the duration of odour exposure should not exceed 90 s, to avoid adaptive phenomena [10].
Sensory testing is used to classify odours according to.
-Rating of acceptability by untrained panel (yes/no question; continuous scale from "clearly acceptable" to "clearly unacceptable");   -Rating of intensity with a comparative scale by a trained panel (sensory comparison between the sample and a series of concentrations of a calibrated reference substance (e.g.acetone)); -Rating of intensity with a category scale by a trained or untrained panel; -Rating of hedonic tone by a trained or untrained panel (scale from − 4 (extremely unpleasant) to +4 (extremely pleasant) with a neutral point); -Evaluation of odour quality through descriptive verbal classifications [64].
Panel members undergo an olfactory test [23,64] to assess their ability to identify odours, their intensity and discriminate between different odours.

Discussion
The 93 reviewed papers on PAQ in offices present diverse evaluation methodologies, often not standardized by any specific standard.In almost all cases, they share the approach of considering the condition of olfactory neutrality as the most satisfactory for individuals.The following paragraphs discuss the various assessment methods for PAQ in office buildings towards the introduction of a smellscape approach for the indoor built environment.

Assessment methods of PAQ in office buildings
International standards such as CEN 1752 [12], ISO 16814 [4], and ISO 17772-1 [13] define categories of PAQ to be evaluated using proxies obtained through instrumental measurements, such as CO 2 concentrations, ventilation rates, or Decipol index.These evaluations necessitate the presence of qualified personnel and specific instrumentation.Probably due to this limitation, researchers often rely on human feedback using questionnaires, which are more cost-effective in distribution.The collection of subjective feedback is also adopted by practitioners, as recommended by leading building certification protocols such as WELL and LEED.
When evaluating PAQ, questions commonly target two objects of evaluation, i.e. a general assessment on IAQ (e.g., "How do you perceive the current quality of the air in the room?" [68]) or odours (e.g., "Are there unpleasant odours in the room?" [99]).In the former case, a 7-point Likert satisfaction scale is used in most cases, ranging from "very dissatisfied" to "very satisfied" [25,27,28,30,32,35,36,55,56,61,69,76,77,83,85,91,[93][94][95][96][97]106,108].This scale resembles the 7-point satisfaction scale which is standardized in the case of thermal comfort [124] but is not standardized in the case of PAQ.In the latter case, odours are normally evaluated using a continuous intensity scale (from "no odour" to "overpowering odour") [22,23,39,40,59,72,80].This scale can be found in sensory testing standards such as ISO 16000-30 [10] and ISO 16000-28 [11].Choosing to evaluate IAQ in general or specifically odours shifts the focus from a broader, complex concept to a more specific, sensory one.The first object of evaluation has the power to encompass a wider range of aspects that are part of PAQ, such as irritations or visibility issues (in terms of smog or chemical fog) caused by certain pollutants.
In order to assess the two different evaluation objects, a total of 37 different evaluation scales are used in literature (Table 3).Choosing one evaluation scale over another can potentially influence the results, as each scale involves different methods and thresholds for calculating PD.This can compromise the meta-analysis of the data and thus the formation of substantial scientific evidence on the subject.
In conclusion, there exists a gap in the standardization of PAQ assessment methods.Standards often recommend indices that are not practically utilised.In literature, the evaluation scales that are employed often differ from study to study, making comparisons between the different papers challenging due to the lack of consistency.

Beyond odour neutrality towards an indoor smellscape approach
The assessment of PAQ in offices revolves around the percentage of people perceiving the air as unacceptable.The focus of the reviewed papers is primarily on evaluating factors that negatively impact human experience, with no consideration for those positively influencing the perception of office air quality.One of the most commonly perceived aspects of IAQ by individuals is odours, which is normally characterized using intensity scales (from "no odour" to "overpowering odour").
According to the reviewed papers, an indoor office environment is deemed as satisfactory if it reflects a condition of olfactory neutrality, meaning people do not perceive any odour [59,99,111].If an odour is detected, individuals are considered dissatisfied, and the environmental quality is deemed unacceptable.
This approach is also shared by international standards and regulations.ISO 28802 states that "it can be reasonably assumed that if a person rates an environment as 'smelly,' then they would prefer no smell at all." [14].In this sense, the term "smell" itself is assumed just with a negative connotation.
However, this is a research gap as neutralizing odours might not always be the ideal solution.The presence of pleasant olfactory stimuli can be perceived as more comfortable than the complete absence of detectable odours [125], positively affecting people's mood, well-being, health, satisfaction (also in other domains), and behaviour across various everyday situations, such as spending patterns or increasing productivity [126,127].
In the practices of assessing and designing IAQ, there could thus be a shift from perceiving odour as a "waste" to seeing it as a potential "resource".This involves shifting the focus from odours that cause discomfort to those that can potentially be pleasant.This paradigm shift in the target of building design from a neutral to a potentially pleasant condition for humans has already been made in other IEQ domains (Fig. 6).In the thermal domain, research has progressed beyond the conventional approach based exclusively on the steady-state heat balance equation, which posits 'neutrality' as the optimal state for occupant comfort.This has evolved towards the concept of thermal alliesthesia, which acknowledges that people can find pleasure in a broader range of thermal conditions, depending on the context and the human physiological conditions [128].In the acoustic field, there has been a transition from focusing on noise issues to valuing sound as potentially a design resource through the introduction of the indoor soundscape approach, where soundscape is defined as the "acoustic environment as perceived or experienced and/or understood by a person or people, in context" [129].Similarly, in the visual domain, environmental satisfaction is no longer solely determined by illuminance levels (lux).Instead, researchers have been exploring the effects of the context (e.g., window view quality) and non-visual effects (e.g., circadian lights) on perception [130,131].
Unsurprisingly, in recent years, there has been a growing interest in the concept of smellscape in the built environment [132].In 1985, Porteous introduced the smellscape concept [133], described as the smell environment perceived and understood by a person in a place.Distinguishing between "smell" (i.e., a sensation detected by inhaling airborne molecules of a substance) and "odour" (i.e., the combined substances in the air causing olfactory sensations), the former emphasizes the human experience as a perceptual construct, making it a user-centred approach within the built environment community.This definition originated and is used in outdoor settings [134], but it could be adapted to indoor environments.Drawing on the definition of indoor soundscape, the indoor smellscape could be defined as the smell environment perceived and understood by a person in an indoor context.The term "context," as opposed to the original term "place" used in Porteous's definition [133], also accounts for social, cultural, and historical aspects [135].The indoor smellscape approach will be seen as an expansion of the "traditional" odour control approach.The traditional approach focuses only on "odours", which are "combined substances in the air  causing olfactory sensations," and which carry a negative connotation.On the other hand, the "smellscape" approach will talk more generally about "smells" meaning the "sensations detected by inhaling airborne molecules of a substance" ", with possible negative or positive connotations.Fig. 7 shows a graphical synthesis of the proposed paradigm shift towards the definition of a framework of an indoor smellscape approach.
To move towards an approach that accounts for human experience in the olfactory stimuli of indoor environments, it is essential to understand the main dimensions underlying olfactory perception, along which assess people's perception of the olfactory environment (e.g., in POEs).However, to date, indicators contributing to the emotional dimensions of smell perceptions are not yet fully understood, and a model of indoor smellscape perception is still lacking.This gap is partly due to the fact that smellscape studies have primarily focused on the outdoor environment [134].Additionally, there is a lack of studies attempting to link the chemical characterization of olfactory stimuli that could potentially elicit positive perceptual responses in occupants.Indeed, existing studies have investigated pollutants such as carbonyl chemicals and volatile organic compounds (VOCs) with the aim of correlating high levels of these substances with people's discomfort in relation to odours (and generally to a poor PAQ) [64,67,101].

Future research directions
This review has painted a complex picture of the methods for assessing PAQ in office buildings.A possible definition of the indoor smellscape approach has been introduced, proposing a paradigm shift towards an assessment method and design that focuses on the human experience related to non-neutral olfactory stimuli in indoor environments, leveraging on the hedonic potential of olfactory stimuli.Future work will need to.
-Validate the accuracy of existing evaluation scales towards a standardization.-Study the main dimensions underlying human perception of indoor smellscapes (e.g., arousal, comfort), as already done for other domains [129,135].-Construct a consistent measurement system based on principal component dimension underlying people's perception of indoor smellscapes.This model would be highly valuable in POE studies, as it would indicate the perceptual constructs to be measured and the attribute scales to be employed.Furthermore, understanding human perceptual response to the olfactory environment will be fundamental for filling the gap between predicted and experienced olfactory performance of built environments.Fig. 8 highlights the importance of having a principal component model of olfactory perception to, for instance, measure the effectiveness of an improvement intervention.-Complement the study of the perceptual aspects of indoor smellscapes with instrumental approaches for the chemical characterization of indoor smellscapes.The goal is to model perception based on measurable parameters, moving towards the development of indices that allow for predicting perception based on objective measurements.This would be very useful as it would enable the design of smellscape interventions by predicting the perceptual effect they will generate.-In addition, research will also need to explore the possible effects (positive or negative) on health of a non-neutral olfactory environment.

Conclusions
The current study systematically examined 93 research papers focusing on PAQ in office buildings with the following objectives: (1) to understand the various assessment methods for PAQ adopted in literature studies, and (1.1) to assess whether these methods align with existing standards and protocols.
In a context where there is a lack of shared standardized methods for determining the PD towards PAQ and inconsistencies across literature studies, this paper represents the first comprehensive examination of the topic with a critical perspective.
Regarding the first research question, the main conclusions are.
-In literature, the assessment of PAQ relies predominantly on questionnaires (90 %), with a smaller percentage using alternative methods like Olf and Decipol (2 %), I IAQ (1 %), diaries (2 %), interviews (1 %), sensory testing (2 %), and text mining techniques (2 %) (paragraph 3.2).-Questionnaires evaluate two objects of judgment (IAQ in general and odour) on various components of experience (freshness/stuffiness, quality, comfort, acceptability, satisfaction, perceived odour intensity, and perceived odour character) using different scales (Likert, continuous divided, continuous undivided, open question, checkbox question, multi-choice question, and dichotomous scales) with different number of points.The different scales impact the calculation of the PD, thereby potentially influencing the results and hindering the comparison between studies (paragraph 3.2.3).-The most commonly assessed aspect of PAQ is satisfaction, often measured on a 7-point Likert scale, ranging from "very dissatisfied" to "very satisfied" (paragraph 4.1).-Odours are typically assessed in terms of intensity using a continuous unidirectional categorical scale, ranging from no odour to overpowering odour, with variations in the number of points (e.g., 5 or 6 points) (paragraph 4.1).-In literature, an indoor office environment is considered satisfactory if no odour is present (paragraph 4.2).
Regarding the second research question, the main conclusions are.
-The methods for evaluating PD towards PAQ are not universally standardized by existing standards and protocols (paragraph 4.1).-The evaluation using instrumental indices, which are suggested by standards, are not commonly used by researchers and practitioners (paragraph 4.1).-The satisfaction scale for PAQ, which is mainly used in literature, is not standardized but is adapted from the reference standard for thermal comfort (paragraph 4.1).
Fig. 8. Using a n-dimensions space for target-setting for smellscape design, example of a two-dimensions space developed in analogy to Cain et al. [137].
Each point represents a person's perception of the evaluated smellscape.

Fig. 1 .
Fig. 1.PRISMA flow diagram for the identification of the studies via database.

Fig. 2 .
Fig. 2. Number of PAQ in office articles published per year of publication with respect to the combination of indicated domains.IAQ = Indoor Air Quality; TC = Thermal Comfort; AC = Acoustic Comfort; VC = Visual Comfort.

Fig. 3 .
Fig. 3. Geographical distribution of PAQ studies conducted in offices from 2000 to July 2023.N/S = not specified.

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.Torriani et al.