Environmental monitoring and analysis

Environmental Science (B.Sc) · Environmental management · free study notes for exams, placements and interviews

In short

Environmental monitoring is the planned, repeatable measurement of pollutants and physical parameters in air, water, soil, noise and biota, and the laboratory or instrumental analysis that converts samples into numbers comparable with standards. It is the evidence base for every other environmental activity — a consent to operate, a court case, a compliance report or a pollution control decision stands or falls on how the sample was collected and analysed. Indian practice runs on CPCB/SPCB protocols, the National Ambient Air Quality Standards (2009), the Environment (Protection) Rules, 1986 effluent and emission schedules, and IS 10500:2012 for drinking water, with laboratories recognised under Section 12 of the Environment (Protection) Act, 1986 and accredited to ISO/IEC 17025 by NABL. It is examined in B.Sc/M.Sc environmental science papers, GATE Environmental Science and Engineering (ES paper), UPSC/state pollution board recruitment, and is the core skill tested in interviews at consultancies, EPC firms, CSR/ESG teams and SPCB laboratories.

Explained

What monitoring is, and how a programme is designed

Monitoring vs surveillance vs survey: monitoring is repeated measurement against a defined objective; surveillance is continuous watch for exceedance; a survey is a one-time snapshot (baseline).
Objectives: baseline characterisation, compliance/regulatory reporting, trend detection, source apportionment, process control, health-exposure assessment, research.
Design steps: (1) define the objective and the decision it supports; (2) select parameters; (3) fix sampling locations using wind rose/land-use/flow direction; (4) fix frequency and duration; (5) choose sampling and preservation method; (6) analyse by a standard method; (7) apply QA/QC; (8) compare with standards and report.
Types of sample: *grab (instantaneous)* — one point in time; *composite* — several aliquots pooled, time- or flow-proportional, gives an average load; *integrated* — simultaneous samples from different points mixed. Grab is mandatory for DO, pH, temperature, chlorine, cyanide, oil & grease, coliforms (parameters that change on standing).
Representativeness is the governing idea: a perfect analysis of a bad sample is worthless. Sample size, location, time and handling together decide representativeness.
Detection terms: *LOD* (limit of detection ≈ blank + 3σ), *LOQ* (≈ blank + 10σ), *dynamic range*, *selectivity*, *sensitivity* (slope of calibration), *accuracy* (closeness to true value), *precision* (repeatability, expressed as RSD).

Air quality monitoring

NAAQS (CPCB notification, 18 November 2009): 12 parameters — PM10, PM2.5, SO₂, NO₂, CO, O₃, Pb, NH₃, benzene, benzo(a)pyrene, As, Ni — with one set of limits for industrial/residential/rural areas and a stricter set for ecologically sensitive areas. Key annual/24-h values: PM10 60/100, PM2.5 40/60, SO₂ 50/80, NO₂ 40/80 µg/m³; CO 8-h 2 mg/m³, 1-h 4 mg/m³; O₃ 8-h 100, 1-h 180 µg/m³.
Sampling frequency under NAAQS: 24-hourly values to be met 98% of the time in a year; 2% exceedance allowed but not on two consecutive days. Minimum 104 measurements per year per parameter (twice a week, 24 h each).
Samplers: *High Volume Sampler (HVS)* ~1.1–1.7 m³/min with cyclone/impactor for PM10 on glass/quartz fibre filter; *Fine Particulate Sampler* at 16.67 L/min (1 m³/h) with WINS/sharp-cut cyclone for PM2.5; *Respirable Dust Sampler* combines PM10 filter with gaseous attachments.
Gaseous sampling is by absorption in a reagent in impingers at ~0.5–1 L/min: SO₂ by the improved West–Gaeke (tetrachloromercurate/pararosaniline) method, NO₂ by the modified Jacobs–Hochheiser / sodium arsenite (Na-arsenite) method, NH₃ by boric acid + indophenol.
Continuous analysers (CAAQMS): SO₂ by UV fluorescence, NOx by chemiluminescence, O₃ by UV photometry, CO by NDIR gas filter correlation, PM by beta attenuation (BAM) or TEOM. Data feed CPCB's real-time network and the daily AQI.
Stack/source emission monitoring: isokinetic sampling (sample velocity = flue gas velocity) using a pitot tube, nozzle, heated probe, thimble/filter and impinger train; velocity by S-type pitot, moisture by condensate, gases by Orsat or electrochemical/NDIR analysers. CEMS (continuous emission monitoring systems) are mandated for 17 categories of highly polluting industries with online data transmission to CPCB/SPCB servers.
Indoor/workplace air: personal samplers and area sampling; stack height and dispersion are checked against CPCB's minimum chimney height formula H = 14 Q^0.3 (Q = SO₂ emission in kg/h) for smaller plants.
Limitations: filter-based methods give 24-h averages only, need gravimetric lab conditions; continuous analysers need calibration gases, span/zero checks and high capital/maintenance cost.

Water and wastewater monitoring

Standards: IS 10500:2012 (with amendments) for drinking water — acceptable and permissible-in-absence-of-alternate-source limits; CPCB designated best-use classification A–E for surface water; General Standards for Discharge of Environmental Pollutants, Schedule VI of the Environment (Protection) Rules, 1986, plus industry-specific schedules.
Key EP Rules general effluent limits (inland surface water): pH 5.5–9.0, BOD (3 d, 27 °C) 30 mg/L, suspended solids 100 mg/L, oil & grease 10 mg/L, temperature rise ≤5 °C above ambient; COD 250 mg/L; limits differ for public sewers, land for irrigation and marine disposal.
Field parameters (measure on site): temperature, pH, electrical conductivity, DO, turbidity, free residual chlorine, ORP — multiparameter probes/sondes.
Dissolved oxygen: Winkler's iodometric method with azide modification (manganous sulphate + alkaline KI-azide → acidify → titrate liberated iodine against sodium thiosulphate with starch), or membrane/optical DO probe. DO saturation at 25 °C ≈ 8.3 mg/L.
BOD: oxygen consumed by microbes degrading organics, measured as DO depletion over 3 days at 27 °C in India (5 days at 20 °C internationally); needs seeding, nutrient-buffered dilution water, dilution so that DO depletion is 40–70%.
COD: oxidation by acidified potassium dichromate with silver sulphate catalyst and mercuric sulphate for chloride masking, 2 h reflux at 150 °C, titrate excess dichromate with ferrous ammonium sulphate (FAS) using ferroin; or closed-reflux colorimetric at 600 nm. TOC by catalytic combustion–NDIR.
Solids: total solids (evaporate at 103–105 °C), total dissolved solids (filtrate dried), total suspended solids (filter residue), volatile vs fixed (ignite at 550 °C), settleable solids (Imhoff cone, mL/L).
Other analyses: hardness and Ca/Mg by EDTA titration (Eriochrome Black T), alkalinity/acidity by acid-base titration, chloride by Mohr's argentometric method, sulphate turbidimetrically, nitrate by UV/cadmium reduction, fluoride by SPADNS or ion-selective electrode, phosphate by ascorbic acid–molybdenum blue, heavy metals by AAS/ICP-OES/ICP-MS after acid digestion, pesticides and VOCs by GC-ECD/GC-MS, non-volatile organics by HPLC/LC-MS, bacteriology by MPN (multiple tube) or membrane filtration for total and faecal coliforms (IS 10500 requires absence of coliforms in 100 mL).
Preservation (APHA/IS): cool to 4 °C; H₂SO₄ to pH <2 for COD/TOC/nutrients; HNO₃ to pH <2 for metals; NaOH + zinc acetate for sulphide; no preservative, 6 h holding for microbiology; BOD within 24–48 h at 4 °C.

Noise, soil and biological monitoring

Noise: Noise Pollution (Regulation and Control) Rules, 2000 — ambient limits in dB(A) Leq: industrial 75 day/70 night, commercial 65/55, residential 55/45, silence zone 50/40; day 6 a.m.–10 p.m., night 10 p.m.–6 a.m. Measured with a Type 1/Type 2 integrating sound level meter, A-weighting, slow response, calibrated with an acoustic calibrator; indices Leq, L10, L50, L90, Ldn, NPL.
Soil and solid waste: sampling by grid, random or stratified design; auger/core sampler; depth-wise profiles; coning and quartering to reduce bulk; analysis of pH, EC, organic carbon (Walkley–Black), available N (alkaline permanganate), P (Olsen/Bray), K (flame photometry), CEC, texture (hydrometer/sieve), heavy metals after aqua regia digestion. Leachability by TCLP and, for hazardous waste classification, the Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016.
Biological monitoring: bioindicators (lichens for SO₂, Lemna/algae for nutrients), saprobic and diversity indices, benthic macroinvertebrate scores, fish bioassays (LC50), Ames test and Microtox for toxicity, chlorophyll-a for eutrophication, biomagnification studies in tissue.
Remote and sensor-based monitoring: satellite AOD (MODIS/INSAT), NDVI for vegetation, thermal bands for heat islands, low-cost IoT sensor networks for indicative data (not legally valid for compliance without equivalence testing).

Instrumental analysis — principles

UV-Visible spectrophotometry: Beer–Lambert law; used for nitrate, phosphate, COD, SO₂, NO₂ colorimetry. Needs calibration curve with standards and reagent blank.
Atomic Absorption Spectroscopy: atomise sample in flame (FAAS, mg/L range) or graphite furnace (GFAAS, µg/L) and measure absorption of element-specific light from a hollow cathode lamp; cold vapour for Hg, hydride generation for As/Se.
ICP-OES/ICP-MS: argon plasma at 6,000–10,000 K; multi-element, wide linear range; ICP-MS reaches ng/L (ppt) detection.
Chromatography: GC separates volatile compounds on a capillary column, detected by FID (hydrocarbons), ECD (organochlorines), or MS (identification by mass spectrum); HPLC/IC for ions, phenols, pesticides. Ion chromatography is the standard for F⁻, Cl⁻, NO₃⁻, SO₄²⁻ in one run.
Electrochemical: pH and ion-selective electrodes (Nernst equation), conductivity cells (cell constant), polarographic DO sensors.
Gravimetry and titrimetry remain the reference for solids, hardness, alkalinity, chloride, DO, COD — cheap, robust, no costly instrument, but higher detection limits.

Quality assurance, data handling and reporting

QA/QC elements: method validation, calibration with traceable standards, field blank, trip blank, method blank, duplicate and split samples, spiked sample (% recovery, acceptable ~80–120%), certified reference material, control charts, inter-laboratory proficiency testing.
Chain of custody: labelled, sealed containers with sample ID, location, date-time, preservative, sampler's name and signature, transferred with signatures at each handover — the document that makes data defensible in court or before an SPCB.
Accreditation and legal standing: laboratories must be recognised under Section 12 of the Environment (Protection) Act, 1986 (with State laboratories and government analysts under Sections 52–53 of the Water Act, 1974 and Sections 28–29 of the Air Act, 1981) and accredited to ISO/IEC 17025:2017 by NABL; analysts' reports from such labs are admissible evidence.
Reporting: results with units, method reference, LOD, uncertainty, date of sampling and analysis; non-detects reported as "<LOD", never as zero. Significant figures must match instrument resolution.
Data interpretation: compare with standard; compute exceedance frequency, percentile (98th for NAAQS), moving averages, trend tests (Mann–Kendall), and indices (AQI, WQI).
Public disclosure: CPCB real-time AQI and effluent data portals, SPCB consent conditions, annual environmental statement (Form V, due 30 September each year under Rule 14 of the Environment (Protection) Rules, 1986).

Key points

Representative sample - the single most important requirement; location, time, volume and handling decide validity more than instrument quality.
Grab vs composite - grab for unstable parameters (DO, pH, chlorine, coliforms); composite for average load and mass-balance work.
NAAQS 2009 - 12 parameters, two area categories, 98-percentile compliance, minimum 104 readings a year per parameter.
PM2.5 sampler flow - 16.67 L/min (1 m³/h) through a sharp-cut cyclone; PM10 by HVS at ~1.1–1.7 m³/min.
Isokinetic sampling - stack sampling must draw gas at flue velocity; non-isokinetic sampling biases particulate results high or low.
CEMS - continuous online emission monitoring with data transmitted to regulators; mandated for the 17 highly polluting industry categories.
BOD (Indian convention) - 3 days at 27 °C; international 5 days at 20 °C; depletion must be 40–70% of initial DO.
COD - dichromate oxidation, closed/open reflux 2 h; always ≥ BOD; BOD/COD ratio indicates biodegradability (>0.5 readily biodegradable).
Winkler method - iodometric DO determination with azide modification to remove nitrite interference.
EP Rules Schedule VI - general effluent limits: pH 5.5–9.0, BOD 30, SS 100, oil & grease 10 mg/L for inland surface water.
IS 10500:2012 - drinking water with acceptable and permissible limits; coliforms must be absent in 100 mL.
Noise Rules, 2000 - 55/45 dB(A) residential, 75/70 industrial, day 6 a.m.–10 p.m.
AAS vs ICP-MS - AAS one element at a time at mg/L–µg/L; ICP-MS multi-element at ng/L, costlier.
LOD vs LOQ - 3σ and 10σ above blank; below LOD report "<LOD", never zero.
Spike recovery 80–120% - the routine accuracy check; duplicates check precision (RSD).
Chain of custody - unbroken documented trail; without it data are not legally defensible.
NABL/ISO 17025 + Section 12 recognition - makes a laboratory's report admissible for regulatory and legal use.
Bioindicators - lichens for SO₂, benthic invertebrates and diversity indices for river health; integrate effects over time, unlike instant chemical readings.

Formulas and examples

Beer–Lambert law: A = ε·c·l — A = absorbance (dimensionless), ε = molar absorptivity (L mol⁻¹ cm⁻¹), c = concentration (mol/L), l = path length (cm)

Gravimetric PM concentration: C = (W₂ − W₁) × 10⁶ / V — W₁, W₂ = initial and final filter mass (g), V = volume of air sampled (m³), C in µg/m³

Volume of air sampled: V = Q × t — Q = average flow (m³/min), t = sampling time (min); convert to standard conditions by V_std = V × (P/P_std) × (T_std/T)

BOD (diluted, seeded): BOD = [(D₁ − D₂) − (B₁ − B₂)·f] × dilution factor — D = DO of sample initial/final, B = DO of blank, f = fraction of seed; dilution factor = volume of bottle / volume of sample (mg/L)

COD = [(A − B) × N × 8000] / mL of sample — A = FAS used for blank (mL), B = for sample (mL), N = normality of FAS, 8000 = 8 g O₂/equivalent × 1000 (mg/L)

DO (Winkler) = (mL thiosulphate × N × 8 × 1000) / volume of sample titrated (mL), in mg/L

Equivalent continuous noise level: Leq = 10 log₁₀[ (1/T) Σ tᵢ · 10^Lᵢ/10 ] dB(A); Ldn = 10 log₁₀[(1/24)(15·10^Ld/10 + 9·10^(Ln+10)/10)]

Sub-index for AQI: Iₚ = I_LO + [(I_HI − I_LO)/(C_HI − C_LO)] × (Cₚ − C_LO); AQI = max of all sub-indices (CPCB, 2014; needs at least 3 pollutants including PM10 or PM2.5)

Stack gas velocity (S-type pitot): v = Kp · Cp · √(2ΔP/ρ); isokinetic rate Q_n = v × A_nozzle

Mass emission rate E = C × Q_flue, with C in mg/Nm³ and Q in Nm³/h → E in mg/h (divide by 10⁶ for kg/h)

Water Quality Index (weighted arithmetic): WQI = Σ(Qᵢ·Wᵢ)/ΣWᵢ, with Qᵢ = 100 × (Vᵢ − V_ideal)/(Sᵢ − V_ideal), Wᵢ = K/Sᵢ

Example 1 — PM10 from a high volume sampler. Filter mass before 11.2840 g, after 11.4360 g. Flow averaged 1.2 m³/min for 24 h.

Mass collected = 11.4360 − 11.2840 = 0.1520 g = 152,000 µg.
Air volume = 1.2 × 24 × 60 = 1,728 m³.
C = 152,000 / 1,728 = 87.96 ≈ 88 µg/m³.
NAAQS 24-h PM10 limit is 100 µg/m³ → compliant, but above the 60 µg/m³ annual standard, so a year of such days would fail.

Example 2 — BOD with dilution. 10 mL of sewage diluted to 300 mL. Initial DO 8.0 mg/L, DO after 3 days at 27 °C = 2.4 mg/L. Blank DO fell from 8.2 to 8.0 mg/L; seed correction negligible.

Dilution factor = 300/10 = 30.
Depletion = 8.0 − 2.4 = 5.6 mg/L → fraction depleted = 5.6/8.0 = 70%, just inside the valid 40–70% window.
Blank correction = 0.2 mg/L.
BOD = (5.6 − 0.2) × 30 = 162 mg/L. Against the Schedule VI limit of 30 mg/L, the effluent needs treatment of about 81% BOD removal.

Example 3 — COD by open reflux. 20 mL sample; FAS normality 0.25 N; blank titre 24.0 mL, sample titre 14.6 mL.

(A − B) = 24.0 − 14.6 = 9.4 mL.
COD = 9.4 × 0.25 × 8000 / 20 = 18,800/20 = 940 mg/L.
If BOD of the same sample is 310 mg/L, BOD/COD = 310/940 = 0.33 → only partly biodegradable; chemical or advanced oxidation pre-treatment is indicated before biological treatment.

Example 4 — Leq from a noise survey. Measured in a residential area at night: 60 dB(A) for 30 min, 50 dB(A) for 60 min, 45 dB(A) for 30 min (total 120 min).

Σtᵢ·10^Lᵢ/10 = 30×10⁶ + 60×10⁵ + 30×10^4.5 = 30,000,000 + 6,000,000 + 948,683 = 36,948,683.
Divide by T = 120 → 307,906. log₁₀(307,906) = 5.4883.
Leq = 10 × 5.4883 = 54.9 dB(A). The night-time residential limit is 45 dB(A), so there is an exceedance of about 10 dB(A).

Example 5 — mass emission rate and AQI sub-index.

A stack discharges flue gas at 25,000 Nm³/h with SO₂ at 180 mg/Nm³ → E = 180 × 25,000 = 4,500,000 mg/h = 4.5 kg/h. Minimum chimney height H = 14 × 4.5^0.3 = 14 × e^{0.3 × ln4.5} = 14 × e^0.3×1.5041 = 14 × 1.5725 = 22 m.
PM2.5 24-h average of 95 µg/m³ falls in CPCB's "poor" band (91–120 µg/m³ ↔ AQI 201–300): I = 201 + [(300−201)/(120−91)] × (95−91) = 201 + (99/29)×4 = 201 + 13.66 = AQI ≈ 215 (poor).

Parameter	Method	Container	Preservation	Holding time
pH, temperature	Electrode, in situ	—	None	Immediate
DO	Winkler / probe	Glass BOD bottle	Fix on site	8 h (fixed)
BOD	3 d, 27 °C	Plastic/glass	4 °C	24–48 h
COD	Dichromate reflux	Glass/plastic	H₂SO₄ to pH<2, 4 °C	7 days
Heavy metals	AAS/ICP	Plastic, acid-washed	HNO₃ to pH<2	6 months
Coliforms	MPN / membrane filter	Sterile glass	4 °C, no preservative	6 h
Pesticides	GC-ECD/MS	Amber glass, Teflon cap	4 °C, dark	7 days to extraction

Aspect	Manual (filter/wet chemistry)	Continuous (CAAQMS/CEMS)
Output	24-h or grab average	Minute-level real-time
Capital cost	Low (₹ lakhs)	High (₹ tens of lakhs per station)
Skill needed	Lab analyst	Instrument engineer, calibration gases
Legal status	Reference methods, widely accepted	Accepted where certified and calibrated
Weakness	Delay, no episode capture, handling errors	Drift, downtime, costly spares

Where it is used

SPCB/CPCB laboratories and regional offices: consent-to-operate verification, NAAQS and water quality network operation, prosecution evidence, AQI publication.
Environmental consultancies and EIA firms (e.g. those on the NABET/QCI accredited list): three-month baseline monitoring for air, water, noise, soil and ecology in EIA studies; post-clearance compliance monitoring.
Industry environment cells: cement, steel, thermal power, refineries, pharma and textile units run CEMS and effluent online monitors, in-house labs, Form V environmental statements and ZLD verification.
Commercial testing labs: NABL-accredited analytical labs (water testing for municipalities, packaged drinking water under BIS certification, food and soil testing).
Urban local bodies and water utilities: Jal Jeevan Mission water quality testing, sewage treatment plant inlet/outlet monitoring, Namami Gange river water monitoring.
Job roles: environmental chemist/analyst, monitoring engineer, lab QA officer, EHS executive, ESG data assurance analyst, research assistant in NEERI/IITs/state remote sensing centres.

Interview questions

Q: When would you take a composite sample instead of a grab sample? A: When the aim is an average concentration or pollutant load over time — for example a day's effluent BOD or COD; a grab sample is used for parameters that change on standing, such as DO, pH, chlorine or coliforms.
Q: Why must stack sampling be isokinetic? A: If the sampling velocity differs from the flue gas velocity, inertial separation causes over- or under-sampling of larger particles, biasing the particulate concentration.
Q: Why does India report BOD at 3 days and 27 °C? A: It reflects Indian ambient temperatures and gives roughly the same oxygen demand as the 5-day 20 °C test in a shorter time; the EP Rules limit of 30 mg/L is defined on that basis.
Q: What does a BOD/COD ratio of 0.2 tell you? A: The waste is largely non-biodegradable, so biological treatment alone will not work; chemical or advanced oxidation, or adsorption, is needed first.
Q: Why is azide added in the Winkler method? A: Sodium azide destroys nitrite, which otherwise oxidises iodide and inflates the apparent dissolved oxygen.
Q: How does AAS differ from ICP-OES? A: AAS measures absorption of element-specific lamp light by atoms in a flame or furnace, one element at a time; ICP-OES excites atoms in an argon plasma and measures emission from many elements simultaneously with a wider linear range.
Q: What is a field blank and why is it taken? A: A clean container of reagent water taken to the site, opened, preserved and transported like a sample; it detects contamination from containers, reagents, handling or transport.
Q: What makes monitoring data legally defensible in India? A: Sampling by a prescribed method, an unbroken chain of custody, and analysis in a laboratory recognised under Section 12 of the Environment (Protection) Act, 1986 and accredited to ISO/IEC 17025 by NABL.
Q: How is the CPCB AQI computed? A: Sub-indices are calculated for each pollutant by linear interpolation within its breakpoint band; the AQI is the highest sub-index, and at least three pollutants including PM10 or PM2.5 must be available.
Q: A result comes out below the detection limit — how do you report it? A: As "<LOD" with the numerical LOD and the method stated; reporting it as zero overstates the finding and distorts averages.
Q: Spike recovery in a batch is 55%. What do you do? A: Treat the batch as failed; check matrix interference, digestion efficiency, calibration and standard stability, then re-analyse — recovery is normally expected in the 80–120% band.
Q: Why are 104 readings a year specified under NAAQS? A: Twice-weekly 24-hour sampling gives enough data for a statistically meaningful annual average and for the 98-percentile compliance test.

Common mistakes

Using the wrong container or missing the preservative and holding time — acidified bottles for metals, sterile unpreserved bottles for microbiology, fixing DO on site.
Forgetting the dilution factor in BOD, or accepting a test where DO depletion is outside 40–70%, which makes the result unreliable.
Converting sampled air volume incorrectly, or not correcting to standard temperature and pressure before comparing with NAAQS.
Confusing the 24-hour standard with the annual standard, and declaring compliance from a single day's reading.
Adding noise levels arithmetically instead of logarithmically — two 60 dB sources give 63 dB, not 120 dB.
Quoting instrument readings to more significant figures than the method supports, or reporting non-detects as zero.
Skipping blanks, duplicates and spikes because the schedule is tight, then being unable to defend the data when questioned.