Evaluation of Particulate Matter Pollution in Micro-Environments of Office Buildings—A Case Study of Delhi, India

High level of particulate matter in an office building is one of the prime concerns for occupant’s health and their work performance. The present study focuses on the evaluation of the distribution pattern of airborne particles in three office buildings in Delhi City. The study includes the Assessment of PM10, PM2.5 and PM1 in the different indoor environments, their particle size distribution, I/O ratio, a correlation between pollutants their sources andmanagement practices. The features of buildings I, II, and III are old infrastructure, new modern infrastructure, and an old building with good maintenance. The results indicate that the average concentrations of PM10, PM2.5, and PM1 are found in the range of 55–150 μg m , 41–104 μg m 3 and 37– 95 μgm , respectively in Building I, 33–136 μgm , 30–84 μgm 3 and 28–73 μg m , respectively in Building II and 216–330 μg m , 188–268 μg m 3 and 171–237 μg m , respectively in Building III. The maximum proportion of the total mass contributed by PM0.25–1.0 i.e., up to 75%, 86%, and 76% in the meeting room of Building I, II and III, respectively. The proportion of ultrafine particles was found higher in the office area where the movement was minimum and vice versa. The higher I/O indicates the contribution of the presence of indoor sources for ultra-fine and finer particles. Further, possible strategies for indoor air pollution control are also discussed.


Introduction
Indoor Air Quality (IAQ) refers to the level of air pollutants and thermal (temperature and relative humidity) conditions that affects the health, comfort, and performance of the occupants inside a building. The high concentration of air pollutants indoor is a major concern in Delhi city, which has been many times reported as one of the polluted cities of the world [1]. The major sources in an office building are infiltration of ambient air pollutants; emissions from office equipment like printers, xerox. Etc.; emission of VOCs from building materials, re-suspension of floor dust; emission from cleaning chemicals among them [2]. In addition to the sources, poor ventilation builds the pollutant level indoors [3]. The increasing level of pollutants needs to be managed as it can affect occupant's health, comfort, and work output. Researchers in the past showed evidence that the air within residential and other commercial buildings including offices can be more polluted than the outdoor air even in the largest and most industrialized cities [4][5][6][7]. It is also reported that the health risks may be greater due to exposure of air pollutants indoor than outdoor as people spend more time in indoor environment, be it office or at home.
There are no specific criteria pollutants and standards defined to categorize classes of indoor air quality i.e. satisfactory or hazardous. Generally, researchers focus on the CO 2 level and thermal comfort parameters for Indoor air quality, which are indicators of sick building syndrome [8,9]. There is limited information available on the high exposure of indoor particulate matter in buildings, especially working offices, where people spend almost 8-9 hours daily and are exposed. Limited research is carried out on size segregated PM in indoor air in cities of developing countries where outside PM levels are higher [10][11][12]. Researchers also observed that fine and ultrafine particles are more harmful than coarse particles irrespective of indoor or ambient environments [13].
In the past, Wargocki et al. [14] have experimented in a typical office environment in which two exposure conditions were produced i.e., with and without emission source where the same office staff worked for 5 h in each condition. The productivity of the staff was found 6.5% less in poor air quality and experienced significantly increased incidences of headache i.e., a symptom of sick building syndrome [15]. Fisk [16] concluded relatively strong evidence of relationships among characteristics of buildings and indoor environments, which influence the occurrence of communicable respiratory illness, allergy and asthma symptoms, sick building symptoms, and worker performances. It is also reported that any improvement in IAQ by a factor of 2-7 can increase occupant's productivity in offices.
In the recent past, some studies are carried out to assess the Indoor PM 10 and PM 2.5 levels in school buildings and residential buildings in different Indian cities ( Table 1). The major objectives of these studies were to assess PM exposure on children, who are more sensitive [22,23,26]. Kulshreshtha   concentrations in the range of 197-713 μgm À3 in winter and 34-60 μgm À3 in summer while PM 1 found in the range of 169-623 μgm À3 in winter and 23-36 μgm À3 in summer, respectively in a low and medium-income group house where emissions from kitchen are generally high due to Indian cooking style. The results indicate a higher level of PM concentration during the winter season. However, the level of PM 2.5 and PM 10 in western cold countries is comparatively very less [19,25].
Recently, Gupta et al. [25] have reported PM 2.5 concentration level as 116 AE 67 μgm À3 in one of the office buildings in Delhi during the winter period. The higher level of PM 2.5 might be due to the penetration of ambient PM 2.5 , which is generated from nearby high traffic roads. The high level of indoor PM (PM 10 ,PM 2.5, and PM 1.0 ) in the office building is an emerging issue in view of its adverse effects on working productivity and health. There is a need to assess it comprehensively at different locations in the city for different types of office buildings.
The present study is an attempt to assess the size of fractioned PM in different sections of the office buildings. The study has monitored the different size PM in different building sections like staff cabin, meeting/conference room, office halls, accountant room, and outside building in Delhi city. PM monitoring is carried out in three different types of buildings. The particle size distribution plot of each monitoring location has been carried out and compared to further correlate with the sources. The correlation between sites for a particular size PM is calculated along with the Indoor/outdoor ratio.

Site description
Three different types of office buildings are considered in the present study to assess the PM levels in the indoor environment. The buildings are named Building I, Building II and Building III located at sites I, II and III, respectively. Sites I and II represent South Delhi, while site III represents Central Delhi, as shown in Figure 1. Building I is a traditional office building with old infrastructure, Building II is a newly constructed office space (with Modern Infrastructure) and Building III is an old Building, but maintained very well. The details of the buildings and surrounding site features are described in Table 2.

Instrumentation and monitoring protocol
PM monitoring was carried out using a laser aerosol monitor (GRIMM Aerosol Technik Gmbh & Co. KG, Ainrig, Germany, Mini-LAS Model 11R) [27]. The instrument captures every single particle ranging from 0.25 to 32 μm and classifies it into 31 size range channels. The instrument was calibrated before monitoring. The data were recorded and stored at every 6-second interval. The monitor provides concentration levels at the cut of point of PM 1.0 ,PM 2.5 ,andPM 10 which are generally monitored for health exposure and from a regulatory compliance point of view.
Monitoring was carried out for 1 day each at all the three sites in December 2018 (Winter) on different dates. At each location of the building at all three selected sites, 15 minutes of measurement was recorded. The monitor was placed in the center of each room (about 1 m above the floor), which corresponds to the breathing zone of the sitting occupants, and the outdoor monitor was placed at least 1.5 m away from any obstacle at a height of 1 m above the ground. The details of the monitoring protocol followed are summarized in Table 3. The photographs of monitoring locations for Buildings I and II are shown in Figure 2, whereas photographs were not taken at site III due to security reasons. Based on the discussion with the office staff about their comfort and visualizing the situations of the Heating, Ventilating and Air Condition (HVAC) system, in each compartment of all three buildings, building I am categorized as poor ventilated, however, buildings II and III as good ventilated. Kulshreshtha

Status of indoor PM 10 ,PM 2.5, and PM 1 concentration
Generally, the particles are monitored in terms of PM 10 (particles having aerodynamic diameter ≤ 10 μm), PM 2.5 (particles having aerodynamic diameter ≤ 2.5 μm), and PM 1 (particle having aerodynamic diameter ≤ 1.0 μm) for regulatory as well as health exposure assessment in ambient as well as in the indoor environment. Additionally, the particles are defined as Ultrafine (<1 μm), Fine or accumulation mode (1 to 2.5 μm) and Coarse particle (> 2.5 μm) as described by Tiwary & Williams [28]. A similar assessment was carried out in the present study as well to evaluate the level of these particles. The monitored data of PM 10 ,PM 2.5, and PM 1.0 concentrations were analyzed statistically and are summarized in graphical form in Figures 3 to 5 for Buildings I to III, respectively.  Table 3.
Monitoring protocol adopted in each building.
The average concentrations of PM 10 ,PM 2.5, and PM 1.0 in Building I were found to be 101 μgm À3 (range 55-150 μgm À3 ), 72 μgm À3 (range 41-104 μgm À3 ) and 64 μgm À3 (range 37-95 μgm À3 ), respectively. The concentration of particulate matter was found higher in the account's department compartment and Halls E and  Hall A, which might be due to higher activities and deposition of particles on files that move here and there on daily basis along with the staff.
At Building II, the average levels of PM 10 ,PM 2.5, and PM 1 were 88 μgm À3 (range 33-136 μgm À3 ), 70 μgm À3 (range 30-84 μgm À3 ) and 63 μgm À3 (range 28-73 μgm À3 ), respectively. The concentrations of all three fractions of PM were found higher at the reception area and in the cafeteria/ pantry area, which is directly correlated with the high activity area. The high level of PM 10 at reception and halls A and B (next to the reception area) might be due to the high movement of staff and visitors in the office compared to other office areas.
At Building III, the concentrations of PM 10 ,PM 2.5, and PM 1 were found in the range of 119-129 μgm À3 , 102-106 μgm À3 and 90-99 μgm À3 , respectively during non-meeting hours, however, these values during meeting hours were found to be high as 216-330 μgm À3 , 188-268 μgm À3 and 171-237 μgm À3 , respectively. This difference might be due to the penetration of PM due to the opening and closing of doors from the entrance gate to the lobby area and then the lobby gate to outside due to the high movement of people. The meeting was going during the monitoring and about 60-70 persons were present in the meeting hall.
Each of the compartments of respective buildings varied notably in dimension, number of doors, frequency of closing and opening, and the number of units of air filtration vents as described in Tables 2 and 3. The combination of these variables provided highly variable ventilation conditions and huge differences in indoor PM concentrations. A higher proportion of ultrafine particles also indicates the possibility of bio-aerosols in indoor spaces, which needs to be assessed and managed from a health impact point of view.
Further, the correlation between the size of the room/halls (indoor volume, m 3 ) and size segregated particulate concentrations were estimated for Building I and II.  The correlation coefficient (r 2 ) values for PM 10 ,PM 2.5 and PM 1 were estimated to be À0.35, À0.55, À0.54, respectively at Building I and À 0.19, À0.28, À0.28 at Building II. The negative correlation means larger halls/rooms increase the dispersion of particles, which results in low concentrations. It is also important to note that particulate concentrations at Building I (Old infrastructure and poor ventilation) have a good negative correlation with the size (volume) of the indoor compartments/rooms as compared to Building II (Modern infrastructure and good ventilation). It might be due to the impact of a good ventilation system, which dominated the impact of room size. Further, the fine and ultra-fine particles have a good correlation with the size of the room compared to coarser particles.

Particle size distribution in indoor work environment
The particles in the atmosphere may be primary or secondary, solid, or liquid depending upon their formation/sources. In the air, particles remain in suspended form for a longer time depending upon their sizes, which vary from very ultra-fine particles (nm) to coarse fine particles (μm). In literature, it is reported that ambient air particles below 2.5 μm are called fine particles which are further divided into transient nuclei (<0.1 μm) and accumulation range (0.1-2.5 μm). The fine particles are mainly generated due to primary emissions (controlled combustion activities, bio-aerosols, secondary aerosol, room air freshener, room cleaner spray in Indoor environments etc.). The particles in the size range of 2.5-100 μm are called coarse particles and are generated from wind-blown dust, sea spray etc. [29,30].
In the present study, particle size between 0.25 μmto32μm is monitored at different 31 intervals. The fraction of different sized particle mass is compared between different indoor work environments and then with the ambient air. The fraction of total mass (%) contributed by different size range particles are described in Tables 4-6 and Figure 6.
In Building I, the maximum mass was contributed by particles of size range 0.25-1.0 μm, in the range of 33-55% in Halls (Staff sitting area with half-sized individual cabin). These values for meeting rooms were even higher, being in the range of 60-75% (empty room during monitoring). The second dominant particle size range was 2.5-10 μm, which contributed 27-40% of the total mass in Halls, 12-21% in meeting rooms, however, the contribution at the common building entrance was 38%. The proportion of particle size 10-32 μm was between 11 and 24% (except Hall D, 5% only), 4-7% in meeting rooms, and 18% at the common entrance gate. In ambient air the mass contribution by particles of size 0.25-1.0 μm, 2.5-10 μm and 10-32 μm was found as 7%, 48%, and 41% respectively, which seems to be opposite to the trend of mass distribution in the different indoor environment except for the common entrance area.
In Building II, which is a modern office and located in the lower ground floor of a shopping mall (no direct opening in the ambient environment), the trend of particle size distribution was more or less similar with more percentage of ultrafine particles (0.25-1.0 μm); in the range of 36-64% in Office Halls, 82-86% in conference/meeting rooms, 30% at Main entrance of the Mall. In this building, the pantry area is near to the office staff sitting area and where the dominant particle size range was 2.6-10 μm with 40% of the total mass.
In Building III, a similar trend was observed for the meeting hall and common Indoor lobby area during non-meeting hours. However, during meetings, the proportion of ultrafine particles decreased from 78-64%, whereas particles of 2.6-10 μm increased from 13-22%. This indicates the re-suspension of particles due to the movement of people in the indoor environment. In the meeting hall, approx. 60-70 people were present during the meeting, which enhanced the particle concentrations even in the presence of sufficient ventilation systems.  Table 4.  Table 5.

Proportion of mass (%) contributed by different size particles in different indoor compartments of building II.
It is observed that the proportion of finer particles is maximum in the indoor environment where the activity level is minimum (meeting rooms), followed by staff sitting area and then common building entrance (high people movement). It indicates that ambient air particles are more influenced by windblown dust particles from road and construction dust and natural dust. The particle size distribution indoor indicates the possibility of accumulated particles and bio-aerosol which are generally found in the range of fine particle size (diameter < 1 μm).  Table 6.
Proportion of mass (%) contributed by different size particles in different indoor compartments of building III. Norhidayah et al. [31] also found a dominant particle size range 0.3-0.5 μminan office building in Malaysia and reported printing and photocopier machines as the major source of particles which is supported by work carried out by Massey and Taneja [13]. They have found that photocopier and printer machines generated accumulation phase particles i.e., 0.25-1.0 μm, and air freshener and cleaner generate particles of size l μm. Similarly, Tang et al. [32] reported a significant increase in fine and ultra-fine particle concentration in 43 out 62 office's rooms. They reported the average size of emitted particles in the range from 0.23 and 20 μm.

The ratio of Indoor/Outdoor (I/O) PM Concentrations
The  In Building I, the I/O of ultrafine particles (0.25-1 μm) was found higher as compared to fine and coarse sized particles in all indoor compartments of the building. The I/O ratio of ultra-fine particles in the meeting/conference room (nonactive area) was found maximum in the range of 1.6-1.7 when compared to other compartments of the building where office staff movement was more (0.5-1.1). Secondly, particles of size 1.1-2. 5  The I/O ratio pattern of Building III is more or less similar to Building I during non-meeting hours which is found to be 0.8, 0.3, 0.2, and 0.1 in the meeting hall for particle sizes of 0.25-1.0 μm, 1.1-2.5 μm, 2.6-10 μm and 10.1-32 μm, respectively. However, during meeting hours, these I/O values were found to be higher as 1.9, 1.4, 0.7 and 0.3, respectively. The occupants found the I/O ratio in Building III higher because of the opening and closing of the door many times during the monitoring period.
It is inferred that fine and ultrafine particles have higher I/O at all three sites, which might be due to the presence of Indoor sources and/or poor ventilation. Building II and III are well maintained, ventilated, and have modern infrastructure compared to Building I. This is reflected by low I/O values in all indoor compartments of Building II compared to Building I for ultrafine and fine particles. At Building III, there were no open files on desks, no cafeteria activities like Building II, however, still I/O was found >1 for the finer particles. Based on the discussions, it was found that regular cleaning of the tables, chairs and other areas was carried out through cleaning spray in the meeting room, which might generate fine aerosols. Similar observations were found by Goyal and Kumar [33], they found that I/O ratio for PM 10 ,PM 2.5 and PM 1.0 varied from 0.37-3.1, 0.2-3.2 and 0.17-2.9 respectively, at a commercial building in Delhi city. In one of the office buildings in Delhi, the I/O ratio of PM 2.5 was found to be 0.28-1.07 μgm À3 , which indicates that indoor PM 2.5 sources exist in the building apart from infiltration from outdoors [25]. The findings in developed countries also indicate average I/O ratios of PM 2.5 between 0.4 and 0.9 in an office room in Beijing and Xi'an cities in China [34,35] and 0.62 AE 0.14 in Milan, Italy [36].
The analysis indicates that fine and ultrafine particles are dominantly generated from indoor activities at the monitoring location, which is not directly connected with outdoor gate (e.g. reception area, common entrance area etc). High I/O ratio for ultrafine and fine particles neglect the hypothesis of intrusion of outside PM in a mechanical ventilated building as coarse particles do not have such trend in I/O ratio.

IAQ management approach
Adequate and properly designed ventilation systems are the most effective strategies for achieving IAQ objectives. Smart planning of building uses and internal layout may help prevent many unnecessary IAQ problems. The mixed-use buildings having common facilities like Xerox facilities, pantry area among others should be properly ventilated and disconnected from the main office sitting area by the air-filter. There should be proper storage spaces for the old office records. The partitioning of the layout may affect the effectiveness of air distribution resulting in stagnant zones with poor air quality, which needs to be taken care of by architectural planning and ventilation engineering. Housekeeping is important in preventing IAQ problems as it keeps dust levels down and removes dirt, which could otherwise become sources of contamination, including mold growth. The cleaning schedule should be arranged according to occupancy patterns and activity levels. Daily cleaning of surfaces and vacuuming of floors is advisable for areas with high occupancy or which are in constant use during the day. The use of eco-friendly or non-toxic chemicals for cleaning also improves IAQ.
Numerous studies are available that strongly suggest that foliage plants in offices may improve health and reduce discomfort symptoms [37,38] Kobayashi et al. [39] tested more than 20 plants to improve indoor air quality. Gawrońska, & Bakera [40] concluded that Spider plants (Chlorophytum comosum L.) phytoremediation particulate matter from indoor air. Torpy & Zavattaro [41] tested Chlorophytum comosum (Spider Plant) and Epipremnum aureum (Pothos) and concluded that indoor green plants can significantly reduce particulate matter concentration and hence improve Indoor Environment Quality (IEQ).

Conclusion
The study has focussed on the assessment of size segregated particulate matter (PM) in different indoor environments of three office buildings located in different parts of Delhi city. The PM concentrations were found higher in the indoor environment where activities were high but had poor ventilation. The levels of PM in the old building were found higher compared to the newly built office building having the modern infrastructure and well-maintained activities/files etc. The presence of people and activities generated re-suspended particles greater than 2.5 μgm À3 , which is noticed when compared PM concentration in the common area, reception area with office cabin area and meeting room with and without meeting hours. The indoor/outdoor ratios were greater for ultrafine and fine particles than coarser particles, which indicates presence of sources of finer particles indoors in all three buildings. Further, the meeting room/conference hall has a higher portion of ultra-fine particles of the total PM concentration. Further, correlation between room size (Indoor volume) and size segregated PM concentration found good negative correlation with finer particles in both buildings. This helps the indoor air quality managers to decide the suitable technology for the improvement of IAQ in different compartments of an office building.
Currently, the country does not have any IAQ standards nor have any monitoring protocol for Indoor air quality assessment. Therefore, it is suggested that country should come out with regulatory framework for IAQ assessment in different types of buildings. The findings of the present study suggest that any proposed IAQ standards should cover ultrafine (PM 1 ) and fine particle (PM 2.5 ) instead of coarser particles especially in office buildings.

Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Author details
Saurabh Mendiratta, Sunil Gulia*, Prachi Goyal and Sanjeev Kumar Goyal CSIR-National Environmental Engineering Research Institute, Delhi Zonal Centre, Naraina, New Delhi, India *Address all correspondence to: s_gulia@neeri.res.in; sunilevs@gmail.com © 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.