Current World Environment

Introduction

Rapid urbanisation has increased energy and food demands of humans which significantly affected the N cycle in the past few decades. Inert N₂gas is converted to its reactive forms through anthropogenic processes e.g. fossil fuel combustion, fertiliser manufacturing, sewage treatment, biomass burning etc. According to several studies, increase in reactive nitrogen can cause imbalance in the nitrogen cycle,¹soil acidification,²loss of biodiversity,^3-4eutrophication of ecosystems⁵etc.

Gaseous ammonia (NH₃) is the primary alkaline trace gas that significantly contributes to total reactive nitrogen in the atmosphere and effects the overall acidity of precipitation, cloud water and airborne particulate matter.^6-9Its deposition alters the transport lifetimes and deposition patterns of sulfur dioxide and nitrogen dioxide emissions.^10-12In the urban context, NH₃plays a critical role as a precursor by neutralising acidic species such as HNO₃, HCl, H₂SO₄which act as chemical sink in the atmosphere to yield ammonium salts, constituting the fine mode secondary aerosols (diameter < 2.5µm). NH₃becomes the primary source of nitrate aerosols in the urban air (equation 1).¹³

HNO₃(g) + NH₃(g) ↔ NH₄NO₃(s) ……. (1)

Air quality in urban areas bears a direct correlation to ammoniated aerosols but their precursors are not well quantified.¹⁴Release of NH₃in vehicular exhausts is a major cause of ammonia loading in the urban air. It has been documented owing to the growing efficiency of three way catalysts to reduce NOx emissions and the introduction of selective catalytic reduction (SCR) system in diesel vehicles.^15-16

NH₃Linkages to Sick Building Syndrome

All indoor structures ‘bathe’ in the outside environment. It implies that the air inside the enclosed structures is an extension of the outside air and its quality is subject to change with respect to variations in the outdoor air depending on the permeability of the structure, nature of the pollutant and other factors.¹⁷NH₃has been directly linked to sick building syndrome (SBS) that makes work environment unsafe for employees. In urban areas, NH₃is contributed by construction materials, refrigeration units, chemical storage, household cleaners, tobacco smoke etc. Exposure to highly concentrated levels of NH₃may cause headaches, nausea and burning sensation in eyes, nose, throat and skin. NH₃has been demonstrated as a key player involved in the neuropathophysiology associated with liver failure and inherited urea cycle enzyme disorders.¹⁸Hyperammonemia may also cause cerebral dysfunction involving a wide range of neuropsychiatric and neurological symptoms. Though indoor NH₃is not a widely studied phenomenon but a few reports establish its occurrence and adverse health effects. A research in Beijing demonstrated indoor air pollution due to NH₃and benzene released from the concrete used in a newly built company office.¹⁹Higher indoor concentration of NH₃(3–6 ppm) was measured in the newly built Beijing office when compared to the reference office of the company (used as control) in Stockholm (<0.1 ppm ammonia). Workers in the Beijing office had a higher rate of complaints with respect to lesser work satisfaction and more work stress unlike the Stockholm reference group. Meininghaus et al.²⁰reported NH₃levels as high as 312 µg/m³类的一所法语学校。一些老师和pupils in the school had complained of symptoms such as headaches, dryness of eyes, irritation in the upper respiratory tract etc. Toxicological reference values (TRV) were used for calculating the risk of exposure to the pollutants under study. If the pollutant concentration was below its TRV, it was not seen as a risk for the health end point studied. For non-carcinogenic compounds TRV was based on the sensory irritation symptoms produced after acute exposure and the Nordic Committee on Building Regulations limits were used as a guideline in the case of NH₃(4000µg/m³). However, the risk of developing sensory irritation due to NH₃was found to be negligible in this study. Health risk assessment was also performed by deriving the margin of safety (MoS) which is based on the exposure limits proposed by OEHHA/INDEX values and the actual exposure of the population to a compound.²¹MoS obtained for NH₃exposure in Finland implied negligible health risk in the country. Regardless of the source of its origin, NH₃exceedance may have a significant impact on the environment and health of the inmates, if present above safety limits.

Major sources of NH₃in India

NH₃emissions are not regulated in most parts of the world. Among the source regions of NH₃in South Asia, one of the hotspots is the Indo-Gangetic Plain which is densely populated and has high yielding, fertile croplands along with ample livestock. Extensive use of fertilizers and sufficient contributions from livestock waste have led to a very high concentration of atmospheric ammonia. Irrigation activities in the croplands are associated with periods of fertilizer application and ammonia release. India has the second-largest land area under agriculture and its fertiliser consumption 16.8 Tg in 2012.²²Due to the tropical climate in India, a volatile gas like NH₃easily evaporates in the atmosphere from agricultural fields, soil under vegetation cover, landfills, fossil fuel burning etc. In addition, industrialisation and services, other sources of NH₃emissions such as refrigeration units, vehicular emissions, manufacturing processes, anthropogenic activities etc. play an important role in the urban areas.²³India does not have any policy to control NH₃emissions and reactive nitrogen species. NH₃emission and deposition budget balance also indicates a huge gap suggesting the need of comprehensive studies on NH₃in India.²⁴新德里,最进口ant North Indian city, is flanked by agriculture intensive states like Uttar Pradesh and Haryana on the geographical map of India. Sitting at this location puts Delhi at the receiving end of pollution due to dispersion of pollutants in the atmosphere along with burgeoning sources of pollution of its own. The present study is aimed at measuring the abundance and seasonal changes of indoor NH₃in two urban households that have distinct characteristics of their own such as the underlying difference in anthropogenic activities, dynamic indoor sources, land cover and land use pattern, vegetation cover etc. at the two chosen sites in the densely populated capital city of Delhi.

Methodology

It is understood that very few studies emphasise on the indoor concentrations of NH₃worldwide.²⁵There is a scarcity of adequate literature reporting the rising indoor NH₃in the Indian context, however, various reports have well established the outdoor NH₃concentrations in the urban landscape of Delhi.^26-28Objective of this study was to study the indoor abundance and variation of NH₃, based on the local and seasonal influences in the selected urban households of Delhi. Also, the toxicological risk assessment associated with the present indoor NH₃concentrations was carried out. For this purpose, NH₃concentrations were determined inside both the households from July 2017 to June 2018 on a monthly basis.

Site Description

Delhi covers an expanse of 1,484 square kilometres. It is the capital of India with an ever growing population of over 25 million. It situated between the latitudes of 28°-24’-17” and 28°-53’-00” North and longitudes of 76°-50’-24” and 77°-20’-37” East. For this study, two households (Dwarka household, DH and Mayapuri household, MH) in Mayapuri and Dwarka regions have been selected as sampling sites in Delhi (Fig. 1). Both these urban localities have unique characteristics of their own which makes them suitable for carrying out this study. Their specific features of these areas have been discussed below:

Mayapuri

It is a locality close to western part of Delhi. The coordinates of Mayapuri are 28° 37' 46'' N and 77° 7' 39'' E. It is mainly an industrialized locality having limited residential area and Tihar Jail. Mayapuri supports large industrial facilities producing heavy and light metals, chemicals, treatment plants, and metal dumpyards etc. Automotive services are prevalent in the area. Recycling of metal scraps and sale of vehicle parts are popular business activities of Mayapuri making it one of the biggest market hubs for automotive and industrial spare parts in India. Overall, the place is now a combination of residential flats (DDA and private), commercial and industrial services.

Dwarka

It is located in the south-west district of Delhi. The coordinates of Dwarka are 28°35' 31'' N and 77°2' 45'' E. It is one of the highly planned and developed residential suburbs of the capital with Indira Gandhi International airport in the vicinity. This area is a typical representative of residential land use pattern with vehicular traffic emissions from the nearby NH-8 and Najafgarh road.

Figure 1: Satellite views showing the two sampling locations at Mayapuri and Dwarka areas respectively. Click here to view Figure

Table 1 describes the features of the two representative households, DH and MH, which have been selected as sampling sites at the Dwarka and Mayapuri areas of Delhi respectively, for the present study.

Table 1: Features of the sampling site households.

Sites Indoor Features	Dwarka家庭(DH)的网站	Mayapuri household (MH) site
Building Features:
Age of Building	Ì´ 20 years	Ì´ 40 years
Sampling point height (from the ground)	Ì´ 50 feet above the ground.	Ì´ 30 feet above the ground.
Roofing and wall construction material	Bricks and concrete.	Bricks and concrete.
Paint on walls	Emulsion paint	Whitewash
Ventilation
Type	Natural ventilation (For e.g. Doors, Windows) Mechanical ventilation (only ceiling fans)	Natural ventilation (For e.g. Doors, Windows) Mechanical ventilation (only ceiling fans)
Cross ventilation	Present	Present
Central heating / cooling system	Absent	Absent
Vicinity Features
Traffic	Less frequency	High frequency
Gardens / Parks	Public parks and gardens.	Absent
Attached garage	Absent	Absent
Indoor Livelihood
Size of the family	4 members (all adults)	5 members (all adults)
Fuel type used in kitchen	LPG	LPG
Household cleaners	House cleaners such as toilet bowl cleaners, floor cleaners, glass and window cleaners etc. are used.	House cleaners such as toilet bowl cleaners, floor cleaners, glass and window cleaners etc. are used.
Furniture type	Wooden and foam furniture	Wooden and foam furniture
Tobacco smoke	Absent	Absent
Food preferences in the family	Strictly vegetarian	Vegetarian and non-vegetarian

Sampling Method

NH₃was collected using a low volume pump at the rate of 1 LPM maintained with the help of a flowmeter. Air was sucked through an open face filter pack, and it was connected to the impinger containing the absorbing solution through silicon tubing. Ammonium aerosols do not get dissolved in the absorbing solution because they are deposited on the PTFE filter (47mm diameter) mounted on the open face filter pack, in front of the entire assembly.²⁶Absorbing solution of 25mM H₂SO₄was used to collect NH₃. Sampling was carried out from July 2017 to June 2018 on a basis of 8 hours during the daytime (9:00 am to 5:00 pm) for a period of 7 days mostly every month. Sampling of NH₃could not be done in April 2018 at both the sites owing to some problems.

Chemical Analysis

NH₃samples obtained at both the sites were analysed in the laboratory by the indophenol blue method using a UV-Vis spectrophotometer. Indophenol blue dye was formed in the sodium pentacyanonitrosylferrate catalysed phenol-hypochlorite reaction with NH₃in alkaline solution. The colour intensity was directly proportional to the amount of NH₃present in the sample. The intensity of resultant ammonium ions complex was determined at a wavelength of 630 nm.

Results and Discussion

Indoor levels of NH₃

Indoor NH₃concentrations ranged from 1.3 to 241.2 µg/m³at the MH site and from 32.5 to 254.5 µg/m³at the DH site. Table 2 shows the descriptive statistics of NH₃at the two selected sites. The average values of NH₃were 57.2 and 102.5 µg/m³at MH and DH sites, respectively and the difference in the average values bears a direct relation with underlying outdoor factors in addition to dynamic indoor sources at the two sites. MH site is situated in the vicinity of an industrial area with limited residential and commercial activities. It differs greatly from DH site which is a typical example of a household in a well planned residential area. Indoor sources of NH₃are prominent contributors to the overall indoor gas phase concentrations.^29-30NH₃浓度的家庭可以归结to the indoor sources the such as cleaning agents, cooking, smoking, metabolic activities of inmates etc. and the significantly variable outdoor features such as land cover and land use pattern, anthropogenic activities in the neighbourhood, vegetation cover, atmospheric chemistry, temperature etc. which influence ambient NH₃levels in the air. Table 3 presents a source inventory for outdoor emissions of NH₃around the indoor sampling sites, MH and DH. It has been reported that most Indian sites have abundance of freely available NH₃in the atmosphere.²⁶High concentration of gaseous NH₃at urban sites is directly associated with increase in population, anthropogenic activities and lack of proper sanitation. NH₃emitted from various sources does not find similar concentrations of counter acidic species for neutralisation leading to incomplete titrations of NH₃in the ambient air and therefore its gaseous phase is prevalent in the air.²⁶Indoor concentrations of NH₃are often higher than the outdoor concentrations because the equilibrium is driven towards the gaseous phase (equation 1) in an indoor set up.^32-33

Table 2: Descriptive statistics of indoor gaseous NH₃levels (µg/m³) at MH and DH sites.

Parameters	MH site	DH site
Mean	57.2	102.5
Median	42.0	78.8
Minimum	1.3	32.5
Maximum	241.2	254.5
Number of days	77	80

Table 3: Source inventory for NH₃emissions from different outdoor sources at Dwarka and Mayapuri areas, near DH and MH sites respectively.(Source-31)

AREA		Dwarka	Mayapuri
INDUTRIAL SECTOR	Types of industries	-NA- Dwarka is a residential locality with no industries.	Various industries in Mayapuri Phase 1 and Phase 2: Engineering – 67 Chemical – 19 Metallurgical – 56 Rubber – 39 Textile – 16 Plastic – 25 Food and Pharmaceuticals – 3 Others – 100 TOTAL – 325
DOMESTIC SECTOR	Domestic sources of NH3	Building materials and paints Leftover food and waste materials. Fertilisers added in potted plants, parks and gardens	Building materials and paints Leftover food and waste materials.
EFFLUENT/ SEWAGE TREATMENT	Emissions from treatment plants	1 Sewage treatment plant (Pappankalan STP) in Sector 16D, Dwarka.	12 common treatment effluent plants from various industries.

Figure 2 shows that indoor NH₃remained higher at DH site as compared to MH site throughout the sampling months. Indoor features of the two households have been discussed in table 1 with the primary indoor sources of NH₃identified as metabolic activities of inmates, cleaning agents, cooking, preference for non-vegetarian food containing high protein levels etc. We may assume that the family setup and lifestyle in both the urban households are quite alike barring some aspects which may have similar influence more or less, on emissions of NH₃inside the households. Higher values of indoor NH₃emissions at DH site as compared to MH site can be attributed to a number of surrounding factors apart from within the household emissions at the two sites. Dwarka is a residential suburb of Delhi with a high green cover area between concrete buildings and the household which serves as our sampling location is surrounded by number of municipal parks, trees and vegetation. Volatilisation from the surrounding soil could be contributing to the indoor NH₃emissions at DH site. Increase in NH₃emissions is known to be caused by agricultural sources which have lesser possibility in urban areas. Though, intermittent fertiliser application in the surrounding parks, trees and household plants at DH site cannot be ruled out. Also, proximity to the Najafgarh drain and its branches which hoard plenty of dead and decaying matter may increase the levels of gaseous ammonia in the ambient air, especially during monsoons. On most sampling days (from July 2017 to June 2018), the indoor NH₃levels remained consistently higher at DH site, except few episodes on certain days during the monsoon season when NH₃levels were recorded to be higher at MH site as compared to DH site. Although indoor NAAQS are not defined by the Central Pollution Control Board (CPCB) in India, we have tried to use the limits of ambient air defined by the CPCB. The maximum limit for ambient NH₃(24 hours) has been prescribed as 400 µg/m³by and the recorded values in this study are well below it. Higher indoor NH₃levels were recorded at DH site as compared to MH site which marked increased NH₃occurrence at the site DH with only residential features. Plummeting levels of indoor NH₃at MH site could be attributed to the industrialised surroundings of this site. Acidic species released from the industries and other sources combine with NH₃and these redox titrations convert NH₃在充氨的气溶胶的形式,因此,decreasing its gas phase presence in the ambient air.

Figure 2: Monthly variation of the indoor NH3concentration at the two sampling sites. Click here to view Figure

Seasonal variation of indoor NH₃

Highest concentrations of indoor NH₃were recorded in August with a monthly average of 212.4 and 151.2 µg/m³at DH and MH sites respectively. Previous studies have shown that monsoons show exceedance in the NH₃concentrations owing to factors such as high humidity and temperature, damp conditions, emissions from dead and decaying organic matter etc.²⁶There is a sharp decline in post monsoon period during October as NH₃concentrations dropped to 38.5 µg/m³and 77.4 µg/m³at MH and DH sites respectively. Fig. 3a and 3b reveal that the indoor NH₃concentrations do not show any significant increase at either DH or MH site in the winter months which implies that decrease in temperature does not favour indoor NH₃. As summer season approaches, the NH₃levels gradually increase in the months of March, May, and June at DH site (Fig. 3a) which can be attributed to the higher volatilisation of NH₃at increased temperature inside the household and from the outdoor local sources such as surrounding soil covered with vegetation, trees and large parks. In Fig. 3b, a similar trend is not observed because of the absence of natural greenery in the vicinity of MH site but an abrupt increase in the month of June (78.3 µg/m³)是be due to beginning of monsoon during late June after dry summer months at the. Seasonal contribution of indoor NH₃levels was plotted using pie charts (Fig. 4a and 4b). At DH site, monsoon season (July to September) showed the highest percentage of 41%, followed by summer season (March to June) at 22%. However, both post monsoon season (October) and winter season (November to February) did not show marked variation at 19% and 18% respectively. On the other hand, at MH site, the monsoon season showed higher contribution at 51% but significant seasonal variation was not observed for rest of the seasons (summer at16%, post monsoon at 17%, winter at 16%). It has been reported that at high relative humidity (more than 50%) and temperature, the indoor NH₃concentrations are higher as compared to cold and dry months.³⁴Fig. 5 showed significant R²values between relative humidity and gaseous NH₃levels as 0.66 and 0.70 at DH and MH sites, respectively.

图3:(a)室内NH3concentration at MH during the sampling months. The dotted lines show the mean values and the solid lines show the median or second quartile values within the box. The box plot represents the 25-75thpercentile. Circles represent the outlier values. (b) Indoor NH3concentration at DH during the sampling months. The dotted lines show the mean values and the solid lines show the median or second quartile values within the box. The box plot represents the 25-75thpercentile. Click here to view Figure

Figure 4:Seasonal variation of NH3abundance at a) DH and b) MH sites Click here to view Figure

Figure 5: Correlation between relative humidity and concentration of gaseous NH3at a) MH and b) DH. Click here to view Figure

Calculation of Irritation Potential (IP) and Margin of Safety (MoS) for indoor NH₃

Meininghauset al.,²⁰used toxicological reference values (TRV) to calculate the risk of acute exposure for pollutants (see introduction). The irritation potential for non-carcinogenic NH₃, was expressed as the ratio of pollutant concentration divided by its TRV (4000µg/m³). We use the same for risk assessment of NH₃exposure to indicate health risks, if any, after short term exposure during different seasons at DH and MH sites using equation 2.

IP = C_s/ TRV …….. (2)

Where, IPis the irritation potential of NH₃during a season, C_sis the average concentration of NH₃during a season and TRV is the toxicological reference value for NH₃(4000µg/m³). Table 4 shows the values of IP for NH₃in different seasons. It is clear that the IP ratio for NH₃is less than 1 for all seasons at both the sites DH and MH, which indicates that there is no acute health risk involved due to indoor NH₃exposure at present concentrations.

表4:刺激可能在不同的海洋sons for NH₃at DH and MH sites

	Monsoon	Post-Monsoon	Winter	Summer
IPs(at DH site)	0.041	0.019	0.018	0.022
IPs(at MH site)	0.028	0.009	0.008	0.008

风险描述长期室内exposure to NH₃can be calculated using the MoS (Margin of Safety) concept.²¹MoS is the ratio of limit of exposure (EL) producing no measurable effect in animals (based on major studies describing the appropriate toxicological end limits) divided by the human exposure (E) and is given by equation 3.²¹

MoS = EL / E .….. (3)

EL for NH₃was 300 µg/m³. As per the annual mean concentrations of NH₃obtained in our study and equation 3, the MoS values for gaseous NH₃exposure were calculated as 2.9 and 5.2, at DH and MH sites respectively. It was observed that the E values in our study were far less than the OEHHA toxicological limit (EL) at both DH and MH sites and hence the MoS obtained was above 1 at both our sampling sites, implying that no indoor health hazard was associated with the present NH₃concentrations.

Hazard Quotient for indoor NH₃

Hazard Quotient (HQ) for non-carcinogenic agents can be defined as the ratio of potential yearly average daily exposure to a substance (E) and the reference concentration (RfC) for inhalation exposure (a level below which adverse health effects are not likely to occur). E can be calculated by using equation (4).³⁵

E = C. IR × ED/W × (D/7) × (WK/52) …… (4)

Where, C is the concentration in (mg /m³) of the pollutant (NH₃in this case), IR is the inhalation rate of adults (0.83 m³/h); ED is the exposure duration, W is the average body weight of an adult, D is the days of exposure per week, WK is the weeks of exposure in a year. E values at DH and MH sites were obtained as 12.1 × 10^-3and 6.7 × 10^-3mg/kg/day respectively.

On using RfC for NH₃as 0.5 mg/m³, HQ for NH₃was found as 0.40 and 0.22 at DH and MH sites respectively. The HQ values were <1 at both the indoor sites which represents negligible hazard.

The toxicological limits for NH₃used here have been derived from studies which were conducted in the developed parts of the world. However, their significance for indoor urban set ups in a rapidly developing nation needs to be adequately comprehended. Here, the indoor concentrations of NH₃are much higher as compared to residential buildings in developed countries. The air in most of the indoor spaces in India such as schools, residences etc. is an extension of the outdoor air as the interior environment is under the constant influence of its outdoor surroundings due to natural ventilation.³⁶In the Indian context, emphasis should be laid on adequate ventilation during the construction of a house; for poorly ventilated houses, measures such as a window above the cooking stove and cross ventilation though doors should be considered.³⁷Though the indoor concentrations are higher than the outdoor concentrations yet building up of pollutants till their toxic limits is prevented by frequent dilution of the indoor air by continuous exchange of fresh air masses occurring through doors and windows. Poor air quality is quite common for dwellings with cramped spaces, inadequate ventilation, high occupant density, traditional cooking fuel usage, or less hygienic surroundings in the poverty stricken areas of developing nations. Average 24-h exposure for particulate matter during biomass fuel usage in rural households was 231 ± 109 mg/m³in southern India.³⁸The indoor NH₃concentrations in these cases may increase beyond the acceptable limits which is hazardous for the occupants and need to be studied further.

Table 5: Comparison of indoor air NH₃concentrations at different locations worldwide.

Country	Site	NH3(µg/m3)	Reference
Finland	Newly constructed residential buildings	20-60	34
Finland	Office buildings	1-49	39
Croatia	Near fertiliser plant	32-352	40
France	School building	312	20
China	Newly built student dormitories in Tianjin	300-373	25
India	Household in Dwarka, New Delhi (Urban-Residential)	32.5-254.5	Present Study
India	Household in Mayapuri, New Delhi (Urban-Industrial cum residential)	1.3 – 241.2	Present Study

Comparison of indoor NH₃concentration at different sites worldwide

Table 5 compares the indoor air NH₃concentrations at different locations worldwide. Distinct ambient environments and indoor living conditions lead to variable indoor NH₃globally. Sub-tropical conditions in India facilitate higher NH₃concentration in the ambient air as compared to the colder nations. In addition, developed countries have better living conditions and sanitary arrangements which account for less ammonia release in the indoor environment.

Conclusion

For a simple fact that people breathe more of the indoor air as compared to the outdoor air, indoor air pollution studies hold definite relevance. Reports on indoor NH₃pollution are very rarely seen. The present study has brought to light the abundance of NH₃in two contrasting households representing residential and industrial features of living environment in Delhi. Results have showed seasonal variability in the indoor NH₃levels in naturally ventilated households. There were remarkable underlying differences in the outdoor surroundings of the households, in addition to the more or less common indoor sources of NH₃within the houses. DH site had higher contributions of NH₃in the indoor air throughout the sampling period as compared to MH site and both the sites recorded highest NH₃concentration during the monsoon season. For subtropical countries like India, monsoon and summer seasons offer greater possibility of NH₃release due to putrefaction and increased volatilisation of NH₃at higher temperature. No major seasonal variation was observed at MH site (except during monsoons) which could be due to its industrialised surroundings where alkaline NH₃gets rapidly neutralised.Risk characterisation for NH₃in both the households using relevant toxicological limits for acute and chronic exposure showed that indoor NH₃does not pose a risk to the health of the inmates. Though the present levels of NH₃are not hazardous at the selected sites but it may exert far reaching effects on human health in due course of time and the situation might be worse in less developed congested areas with poor living conditions. Hence, more comprehensive studies on indoor NH₃and its impacts are definitely needed in developing nations as well as worldwide.

Acknowledgement

We are extremely thankful to DST PURSE for financial support. We also want to thank JNU for providing the infrastructure to carry out this study. Author Ankita Katoch sincerely acknowledges the award of Junior Research Fellowship from CSIR-UGC. This study is a part of DRS-Net (Deposition Research Network through students)-India.

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