Sampling and analysis techniques for inorganic air pollutants in indoor air

Figures & data

Table 1. List of inorganic compounds identified in indoor air, their sources, reported indoor concentrations and indoor guideline values.

No.	Pollutants	CAS number	Sources	Indoor concentrations	Guideline Values
Carbon oxides
1	Carbon dioxide (CO2)	124-38-9	Human breath, combustion sources^[^13^,^23^]	269 − 4960 ppmv (schools)^[^24–26^] 294 − 10000 ppmv (residences)^[^23^] 607 − 2249 ppmv (infant bedrooms)^[^27^]	It depends on building type and occupancy^[^28–31^]
2	Carbon monoxide (CO)	630-08-0	Tobacco smoke, wood and gas stoves, kerosene heaters, malfunctioning gas appliances, car or truck exhaust from attached garages^[^32^]	0.4 − 33.0 mg m^-3 [14]^a LOD − 1.6 mg m^-3 (infant bedrooms)^[^27^] LOD − 4.5 mg m^-3 (schools)^[^26^]	100 mg m^-3 (15 min)^b / 35 mg m^-3 (1 h)^b10 mg m^-3 (8 h) / 7 mg m^-3 (24 h)^[^14^] 11.5 mg m^-3 (24 h) 28.6 mg m^-3 (1 h)^[^33^]
Reactive oxygen species
3	Ozone (O3)	10028-15-6	Household air cleaners generating O3, soldering or welding-related hobbies, photocopy machines, outdoor air^[^32^]	0.8 − 114 μg m^-3 (as average, schools)^[^34^] 0.0 − 96.8 μg m^-3 (offices)^[^34^] 0.0 − 32.0 μg m^-3 (infant bedrooms)^[^27^]	100 μg m^-3 (8 h)^[^35^] 0.07 ppmv (8 h)^[^36^] 40 μg m^-3 (8 h)^[^33^]
4	Hydrogen peroxide (H2O2)	7722-84-1	O3-initiated indoor chemistry, air cleaners, cleaning products^[^37^]	–	–
N-containing compounds
5	Nitric oxide (NO)	10102-43-9	Fuel combustion, kerosene and gas stoves, malfunctioning gas appliances^[^32^]	4.9 ± 3.1 μg m^-3 (home with gas appliances)^[^38^] 39.4 μg m^-3 (museum)^[^39^] 25.0 μg m^-3 (office)^[^40^]	–
6	Nitrogen dioxide (NO2)	10102-44-0	Fuel combustion, kerosene and gas stoves, malfunctioning gas appliances, tobacco smoke^[^32^]	13 − 62 μg m^-3 [14]^c 8.5 − 65.8 μg m^-3 (homes)^[^7^] LOD − 88 μg m^-3 (schools)^[^24^] 26.1 μg m^-3 (6 − 68.5μg m^-3) (schools)^d 23 μg m^-3 (3.4 − 56.5 μg m^-3) (offices)^d	200 μg m^-3 (1 h)^[^14^] 40 μg m^-3 (1 year)^[^14^] 20 μg m^-3 (24 h)^[^33^] 170 μg m^-3 (1 h)^[^33^]
7	Ammonia (NH3)	7664-41-7	Building materials, cleaning products, human emissions, tobacco smoke, outdoor air^[^7^]	5.7 − 43 μg m^-3 (homes)^[^7^]^e	200 µg m^-3 [41]
8	Nitric acid (HNO3)	7697-37-2	Complex reactions from nitrogen oxides^[^7^]	< 1.5 μg m^-3^e	–
9	Isocyanic acid (HNCO)	75-13-8	biomass burning, diesel and gasoline vehicles, industrial processes, tobacco smoke^[^9^]	0.15 ppbv (<LOD − 0.55 ppbv; residence)^[^9^]	–
S-containing compounds
10	Sulfur dioxide (SO2)	7446-09-5	Coal combustion, kerosene^[^32^]	1.2 − 21.9 μg m^-3 (homes)^[^7^]^e	500 μg m^-3 (10 min) 125 μg m^-3 (24 h) 50 μg m^-3 (annual) ^[^42^]
11	Hydrogen sulfide (H2S)	7783-06-4	Human bioeffluents, crude Petroleum, natural gas, volcanic gases, hot springs, groundwater, industry^[^43^,^44^]	86 − 600 pptv (museums)^[^45^] < 60 ppbv (households)^[^10^]f 2.5 − 6.3 ppbv (schools)^[^8^]	150 μg m^-3 (24 h) 7 μg m^-3 (30 h odor annoyance)^[^42^]

^a Data varies greatly between studies and in the absence of indoor sources, concentrations of CO in indoor air in European and North American cities are well below the levels of existing air quality guidelines and standards.^[14]

^b Exceedance to this level should not occur more than once per day.

^c Maximum levels associated with the use of gas appliances in European homes are in the range 180–2500 μg m⁻³.^[14]

^d Median concentrations and range of average concentrations in brackets.^[46]

^e Median concentration in different indoor environments.^[7]

^f Median concentration but corresponds also to the limit of detection.

Table 2. Common objectives for an indoor air quality assessment plan and different aspects to be considered in defining the most appropriate strategy for sampling (adapted from Seifert et al.^[49]).

Sampling objective	Sampling condition	Sampling timing and frequency	Sampling duration	Minimum number of samplers	Minimum number of sampling points	Sampling method
Assessing exposure and health risks
Average exposure concentration	Real-life conditions	Two seasons (winter and summer)	Long-term	2–4	1–2^b	Passive or active sampling
Maximum exposure concentration (peak of exposure)	Worst case	Any time	Short-term	1–2	1–2	Active sampling (continuous monitoring)
Studying the sources of symptoms and complaints
Chronic effects	Worst case	Any time^a	Long-term	1–2	1–2	Active or passive sampling
Acute effects	Worst case	Any time^a	Short-term	1–2	1–3	Active sampling (continuous monitoring)
Investigating the effectiveness of a remedy adopted	Real-life conditions	Before and after	Short/long-term	1–2	1	Active or passive sampling
Testing the compliance with indoor air quality guidelines or standards	Real-life conditions/Worse case	Any time	Period of reference value	2–3	1	Active (continuous monitoring) or passive sampling
Characterizing emission source(s) (e.g., cleaning activity, cooking etc.)	Real-life conditions	Before, during and after activity	Short-term	1	1	Continuous monitoring

^a According to activities.

^b Personal sampling.

Table 3. Methods for sampling and analysis of carbon oxides.

Pollutant	Kind of Instrument	Mode of operation^a	Standards	Analysis Technique	Brand (e.g.,)	Accuracy/precision	LOD	Operation range	Ref.
Carbon oxides
Carbon dioxide (CO2)	High precision Automatic analyzer	OnM	ISO 16000-26	Non-dispersive infrared spectrometry (NDIR)	LICOR-Li 840	Accuracy better than 1.5% of reading	10.2 ppmv	0–20000 ppmv	^[^64^]
	Automatic portable indoor air quality monitor	OnM	ISO 16000-26	NDIR	Delta Ohm HD21ABE17 IAQ-CALC 7545	Precision ±3% of reading or ±50 ppmv	n.a	0–5000 ppmv	^[^25^,^27^]
	Low cost sensor	OnM	n.a	NDIR	Aranet4	Precision 0-2000 ppmv ± 50 ppmv or 3 % of reading	n.a	0–9999 ppmv	–
	Automatic analyzer	OnM	n.a	Cavity ring-down spectroscopy (CDRS)	Picarro G2401	Precision < 50 ppbv	<0.04 ppmv	0–1000 ppmv	^[^64^,^82^]
Carbon monoxide (CO)	Automatic analizer	OnM	EN 14626	NDIR	Teledyne Ins (T300)	Precision < 0.5 %; accuracy < 1%	<0.04 ppmv	0–1000 ppmv	^[^77^]
	Automatic Monitor	OnM	n.a	CDRS	Picarro-G2401	Precision 1.5 ppbv at 5 min	<2 ppbv (1 hour average)	0–5 ppmv	^[^64^]
	Automatic portable indoor air quality monitor	OnM	n.a	Electrochemical sensor (EC)	Delta Ohm HD21ABE17, Gray Wolf	Precision ±3 ppmv + 3% of reading	n.a	0–500 ppmv	^[^24^]
	Diffusive sampler (DS)	OffM	n.a	Focaltin Reaction, Photometric determination	Passam	Expanded uncertainty 24.3 % at levels of 10 mg m^-3	0.6 mg m^-3 for a 2-week sampling period	0.5–20 mg m^-3	-

n.a: not available.

^a OnM: on-line monitoring; OffM: offline monitoring

Table 4. Methods for sampling and analysis of reactive oxygen species.

Pollutant	Kind of Instrument	Mode of operation^a	Standards	Analysis Technique	Brand (e.g.,)	Accuracy/precision	LOD	Operation range	Ref.
Reactive oxygen species
Ozone (O3)	Automatic analyzer	OnM	EN 14625 ISO 13964	Ultraviolet Photometry (UV-Pho)	Envea (O342e) Teledyne Ins.(model T400)	Precision 0.5% of reading above 100 ppbv	0.2– 0.4 ppbv	Min: 0–10 ppmv Max: 0–10 ppmv	^[^86^,^87^]
	Automatic analyzer	OnM	n.a	Nitric oxide- Chemiluminiscence (NO-CL)	Teledyne Ins (model T265)	Precision 0.5% of the reading	<0.3 ppbv	0–2000 ppbv	–
	Diffusive sampler. Nitrite-coated filter (DS-IC)	OffM	EN 14412	Ion Chromatography with conductivity/ absorbance detection	Ogawa	n.a	n.a	n.a	^[^90^,^105^]
	Diffusive sampler. Silica gel coated with 4,4′-dipyridylethylene (DS-Spec)	OffM	EN 14412	UV-Vis spectrophotometer	Radiello® Passam	Uncertainty 14.5 % over the whole sampling rate linearity range	2 µg m^-3 for 7 days of exposure	2–400 μg m^-3	^[^24^,^106^]
Hydrogen peroxide (H2O2)	Diffusion scrubber of PTFE with a solution of Ti(IV)-4-(2-pyridylazo) resorcinol (Denuder)	OffM	n.a	HPLC with spectrophotometric detector at 508 nm	n.a	Precision of standard solution between 1.2 % and 2.1%	9 pptv (sampling volume of 55 L)	n.a	^[^101^]
	Monitor	OnM	n.a	Chemiluminescence oxidation of luminol by H2O2 (Luminol-CL)	n.a	n.a	25 pptv	25pptv–100 ppbv	^[^102^]
	Automatic analyzer based on wet chemical dual-enzyme (WCDET)	OnM	n.a	Fluorescence spectroscopy	Aero-Laser (AL 2021)	n.a	100 pptv	100 pptv − 3 ppmv (gas)	^[^104^]

n.a: not available.

^a OnM: on-line monitoring; OffM: offline monitoring.

Table 5. Methods for sampling and analysis of N-containing compounds.

Pollutant	Kind of Instrument	Mode of operation^a	Standards	Analysis Technique	Brand (e.g.,)	Accuracy/precision	LOD	Operation range	Ref.
N-containing compounds
Nitrogen dioxide (NO2)	Automatic Analyzer	OnM	EN 14211 ISO 7996 ASTM D3824-20 ISO 16000-15	Chemiluminescence (Molybdenum catalyst or Photolytic converter) (CL-Mo CL-Pho)	Thermo Scientific, Model 42i, Teledyne, Eco-Physics	Accuracy 10% Precision ± 0.4 ppbv (500 ppbv range)	50 pptv	50 pptv–1 ppmv	^[^114^,^115^]
	Automatic Analyzer	OnM	n.a	Luminol-Chemiluminescence (Luminol- Cl)	Unisearch  Associates, Inc. (LMA 3 D	n.a	<10 pptv	10 pptv–4 ppmv	^[^117^]
	Automatic Analyzer	OnM	n.a	Cavity Attenuated Phase Shift Spectroscopy (CAPS)	Teledyne-CAPS (model T500U)	Precision 0.5% of reading above 5 ppbv	50 pptv	Min:0–5 ppbv Max: 0– 1000 ppbv	^[^118^,^119^]
	Laser	OnM	n.a	Laser-induced fluorescence spectroscopy (LIF)	n.a	Accuracy ± 0.5 %	80 pptv (10 sec)	n.a	^[^120^]
	Automatic Analyzer	OnM	n.a	(Incoherent broadband) Cavity-enhanced absorption spectroscopy ((IBB) CEAS)	n.a	Uncertainty 7.8 %	0.9 ppbv (5 sec)	n.a	^[^122^]
	Difussive sampler with Triethanolamine (DS-TEA)	OffM	ISO 16000-15	Griess-Saltzman method, Spectrophotometry/ion chromatography	Radiello®, Ogawa, IVL, Gradko (Palmes)	Uncertainty 11.9 %	It depends on the sampler. LOQ 1 ppbv for 7 days of exposure (Radiello)	3–130 µg m^-3	^[^66^,^124^,^125^]
	Active sampler with fritted bubblers system (AS-FSB)	OffM	ISO 6768 ASTM D1607-91	Griess-Saltzman method. Spectrophotometry	–	–	It depends on the sampler	3–2000 μg m^-3 (ISO 6768) 4- 10000 μg m^-3 (ASTM 1607)	–
Nitric oxide (NO)	Automatic Analyzer	OnM	EN 14211	Chemiluminescence (Molybdenum catalyst or Photolytic converter) (CL-Mo/CL-Pho)	Thermo Scientific, Model 42i	Precision ±0.4 ppbv (500 ppbv range)	40 pptv (60 sec averaging time)	50 pptv–100 ppmv	^[^115^]
	Automatic Analyzer	OnM	n.a	Cavity Attenuated Phase Shift Spectroscopy (CAPS)	Teledyne-CAPS (model N500)	Precision 0.5% of reading above 5 ppb	< 10 pptv	Min:0–5 ppbv Max: 0–1000 ppbv	–

n.a: not available.

^a OnM: on-line monitoring; OffM: offline monitoring

Table 5. Continued

Pollutant	Kind of Instrument	Mode of operation^a	Standards	Analysis Technique	Brand (e.g.,)	Accuracy/precision	LOD	Operation range	Ref.
N-containing compounds
Ammonia (NH3)	Automatic Analyzer	OnM	n.a	Cavity ring-down spectroscopy (CRDS)	Picarro G-2103	Accuracy 0.5 ppbv ± 5% of reading Precision of 0.10 ppbv + 0.1% of reading for 30 sec of data.	0.5 ppbv	Guaranteed range 0 − 500 ppbv Operational range 0 − 10 ppmv	^[^64^,^130^,^143^]
	Automatic Analyzer	OnM	n.a	Chemiluminiscence (CL)	ECO physics nCLD 855 CY; Teledyne-API Model T201; Ecotech Pty Ltd model EC9842B	accuracy ± 0.050 ppbv of all the ranges	n.a	0 − 5 ppbv; 0–5000 ppbv	^[^145^,^146^]
	Difussive sampler (DS)	OffM	EN 17346	Ion chromatography/ Flow injection analysis with conductivity detector/ spectrophotometry	Radiello®	Depends on the sampler expanded uncertainty (6.5 % − 29% for 0.001 mg m^-3 )	0.0002–0.0015 mg m^-3 3 for 4 sampling weeks 0.001 mg m^-3 (24 h exposure, Radiello®)	0.0005–0.150 mg m^-3 (depending on the kind of sampler)	^[^147^]
Nitric acid (HNO3)	Annular Denuder Systems (ADS)	OffM	n.a	Ion chromatography	n.a	Precision 2.6 %	0.07 ppbv (24 h sampling at 10 L min^-1)	n.a	^[^150^]
	Difussive sampler (DS)	OffM	n.a	Ion chromatography	n.a	Method precision was ± 3% across 5 calibrations; Accuracy 94 % (upper range standards)	5 pptv (30 day sampling period) or 121 pptv (24 h sampling period)	n.a	^[^154^]
	Continuous automated system	OnM	n.a	Chemical ionization mass spectrometry (Cl-MS)	n.a	n.a	< 50 pptv	n.a	^[^156^]
	Ambient ion monitor	OnM	n.a	ion chromatography	AIM model 9000 D, University Research Glassware Corp, IC (model ICS-2000, Dionex Corp.,)	n.a	14 ng m^-3	n.a	^[^155^,^157^]
	Automatic Analyzer	OnM	n.a	Long path liquid absorption photometer (LOPAP)	n.a	Precision 2-3%, accuracy 10%	5-30 pptv	5 pptv to 400 ppbv	^[^158^]
Isocyanic Acid (HNCO)	Continuous automated system	OnM	n.a	Negative ion proton transfer chemical ionization mass spectrometry (NI-PT-CIMS)	n.a	n.a	0.005 ppbv.	n.a	^[^159^,^167^]
	Continuous automated system	OnM	n.a	Proton transfer reaction-mass spectrometry (PTR-MS)	Ionicon Analytik GmbH)	n.a	2.5 ppbv	low ppbv (2.5 ppbv) up to 1000s of ppbv	^[^162^,^163^]

n.a: not available.

^a OnM: on-line monitoring; OffM: offline monitoring.

Table 6. Instrumentation and measurement techniques for the determination of S-containing compounds in indoor air.

Pollutant	Kind of Instrument	Mode of operation	Standards	Analysis Technique	Brand (e.g.,)	Accuracy/precision	LOD	Operation range	Ref.
S-containing compounds
Sulfur dioxide (SO2)	Automatic Analyzer	OnM	EN 14212 ISO 10498	Ultraviolet Fluorescence (UV-Flu)	Teledyne T100	Precision 0.5% of reading above 50 ppbv	0.4 ppbv	Min:0–50 ppbv; Max: 0 − 20000 ppbv	^[^64^]
	Diffusive sampler with triethanolamine (DS-TEA)	OffM	n.a	Ion chromatography	IVL (Palmes) Ogawa	Accuracy 15%	4 (IVL) − 8 (Ogawa) µg m^-3 (1 day)	0.1–200 μg m^-3	^[^170^,^173^]
Hydrogen sulfide (H2S)	Diffusive sampler (DS)	OffM	n.a	UV/ Visible Spectrophotometry for 24 h exposure.	Radiello® Analyst® IVL	Uncertainty 8.7 % over the whole exposure range	30 ppbv for 1 h exposure or 1 ppbv	–	^[^8^,^177^,^180^]
	Active sampler with-Filter + Sorbent tube. (AS)	OffM	NIOSH 6013	Ion chromatography- conductivity	SKC	Accuracy 11.8 %	11 µg per sampler (0.55 mg m^-3 in 20 L)	0.6–14 ppmv (0.9–20 mg m^-3 ) for a 20 L air sample	–
	Portable H2S gas meters (PGM)	OnM	n.a	Gold film sensor technology	Jerome 631-X	Accuracy ±0.003 ppmv at 0.05 ppmv, precision 5%	<0.003 ppmv	0.003–50 ppmv	^[^178^,^187^]
	Automatic Analyzer	OnM	n.a	UV fluorescence (UV-FLuo)	Teledyne T101	Precision 0.5 % of reading above 50 ppbv	< 0.4 ppbv	0–50 ppbv to 0–10 ppmv	^[^185^]

n.a: not available.

^aOnM: on line monitoring; OffM: offline monitoring.

Table 7. Quality control parameters that must be included in indoor air sampling studies.

Quality control parameter	Description	Frequency	Purpose
Replicate samples	Two or more samples collected simultaneously.	At least 10 % replicate samples per each batch of samples.	To assess repeatability of sampling method.
Laboratory blank	A sampler that is not handled in the field and is stored in the laboratory.	At least one laboratory blank per batch of samples.	To assess contamination from storage in the laboratory.
Field blank	A sampler which accompanies sampler to field and back to laboratory.	At least one field blank per batch of samples.	To assess contamination from transportation of samplers to and from the field.
Series sampling (with active sampling)	Two or more cartridges attached in series.	One series sampling set-up per sampling location with highest expected concentrations.	To detect “breakthrough” and loss of sample.
Backdiffusion (with passive sampling)	Backdiffusion happens when the adsorbed mass of analyte is far from the maximum amount allowed by the adsorbing medium capacity.	It is only necessary to follow the instruction given by manufactures regarding sampling time and concentration of pollutants.	To improve confidence in measured concentrations.
Pump flows (active sampling)	Verification of pump flows by use of calibrated flowmeters. The flow rate should be within a range of ± 5%.	At the start and end of each sampling period.	The start and stop flow rates are averaged to obtain an average flow rate.

Table 8. Parameters for the analytical quality control.

Quality control parameter	Description	Sampling	Analysis	Calculation
Precision^a	Degree of agreement between independent measurement obtained in well-defined conditions (ISO 5725-3:1994^[^190^]). Precision measures the variability associated with repetitive analyses of the same sample.	Data variability may be evaluated by taking field duplicates or multiple air samples at a location.	Data variability may be evaluated with Certified Reference Materials (CRM) and/or laboratory-fortified blanks with analytes at a known concentration (3–5 samples are recommended). Different levels of concentration can be used.	$\mathit{RSD}\left(\mathrm{\%}\right)=\frac{SD}{\overline{X}}x100$ SD: standard deviation $\overline{X}:$ average value
Accuracy^a	It is the closeness of a measurement to the true value (ISO 5725-1:1994^[^191^]). Accuracy can be evaluated with the calculation of desorption efficiency or recovery.	–	Accuracy may be valuated with CRM and/or laboratory-fortified blanks with analytes at a known concentration (3– 5 samples are recommended). Different levels of concentration can be used. Values for acceptable accuracy are define in the international Standards or must be defined if they are not available.	$DE=\mathrm{ }\frac{\overline{X}}{X_{\mathit{ref}}}$ DE: Desorption efficiency $\overline{X}$= average amount recovered $X_{\mathrm{r}ef}$= Spike amount
Linearity (Instrument calibration)	Calibration involves analyzing a series of standards which contain the analytes of interest at several different concentrations.	–	The analytical system must be initially calibrated using a minimum of 5 standard concentrations in the range of expected concentrations in the samples in order to determine the linear response of the target analytes. Continuing calibrations are mid-level calibration standards containing all of the compounds of interest designed to assess the accuracy of an instrument. They are usually run on an on-going (at least daily) basis. It is recommended that the lowest instrument calibration standard be run at the LOD.	By means of a plot of instrument response versus standard concentration. The equation of the plot or the response factor can be used to calculate the concentrations.
Limit of detection (LOD)	It is the smallest measure that can be detected with reasonable certainty for a given analytical procedure.^[^192^] It presents different definitions	–	It can be calculated: from the blank samples, from the signal to noise ratio and from the calibration curve at low concentrations. Laboratories should provide information about the method used to estimate LOD and LOQ. It is recommended that a LOD study be performed twice a year to verify that the values obtained are below the lowest standard used for reporting or for each batch of samplers in case of passive or active samplers using adsorbents. They are usually expressed in units of µg m^-3 for both outdoor and indoor air	$\mathit{LOD}\mathrm{ }or\mathrm{ }\mathit{LOQ}=\frac{k\mathrm{ }x\mathrm{ }SD}{b}$ k: is a factor of 3 (for LOD) and 10 (for LOQ) SD:is the standard deviation of the blank signal, the standard deviation of the ordinate intercept or residual standard deviation of the linear regression b: the slope of the linear regression
Limit of quantification (LOQ)	It is the lower limit of precise quantitative measures.

^a The samples are extracted and analyzed following the same procedure used for field samples

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