Air, water, waste

Environmental monitoring asks a spectrometer to work outdoors, unattended and for long periods. Water, air and soil each have characteristic absorption and emission features, and a field instrument measures them in place. Compact spectrometers with low power draw and stable wavelength calibration are suited for this work.

Water quality

Nitrate absorbs strongly in the UV between about 200 and 240 nm. In-situ UV sensors record the full absorbance spectrum and fit it to separate nitrate from dissolved organic matter and turbidity, which also attenuate light in that region. Absorbance at 254 nm, often reported as SAC254, serves as a surrogate for dissolved organic carbon in drinking water and wastewater treatment.

Fluorescence adds biological information. Chlorophyll-a excited in the blue emits near 685 nm, and phycocyanin from cyanobacteria emits near 650 nm when excited in the orange. Continuous readings of both help utilities and researchers follow algal growth in lakes and reservoirs.

Air quality and emissions

Differential optical absorption spectroscopy, or DOAS, measures trace gases along an open light path of hundreds of meters to several kilometers. The method fits the narrow absorption structures of each gas and removes broad attenuation from aerosols and scattering. Nitrogen dioxide is retrieved in the 400 to 460 nm band, and sulfur dioxide and ozone in the UV below 340 nm. Long paths bring detection limits into the parts-per-billion range. Retrieval quality depends on optical resolution near 0.5 nm and on wavelength stability, since a small shift leaves residual structure in the fit.

Continuous emission monitoring applies the same physics inside a stack or exhaust duct. Nitric oxide, ammonia and sulfur dioxide all absorb between about 190 and 230 nm, so a deep-UV spectrometer can measure the three gases together in one short-path cell.

Soil and agriculture

NIR reflectance reports soil moisture, organic matter and mineralogy. Water absorbs near 1450 and 1940 nm. Clay minerals show an Al-OH feature near 2200 nm, and carbonates absorb near 2340 nm. Calibration models built from laboratory reference data then predict these properties from field spectra, with no chemical preparation. Crop and vegetation studies use visible and NIR reflectance, including the red edge between about 690 and 740 nm, as an indicator of chlorophyll content and plant stress.

Recycling and material sorting

Automated sorting lines identify plastics by their NIR spectra. C-H overtone bands near 1200 nm and 1700 nm differ between PET, HDPE, PP, PS and PVC, which lets a spectrometer classify each item in milliseconds as it passes on a conveyor. The 900 to 1700 nm range of an InGaAs spectrometer covers these bands. Plastics pigmented with carbon black absorb across the NIR, so lines that handle them add other sensing methods.

Key measurements in environmental monitoring

Application	Technique	Measured quantities	Typical range
Water quality	UV absorbance, fluorescence	Nitrate, SAC254, chlorophyll-a, phycocyanin	200–750 nm
Ambient air	DOAS	NO2, SO2, O3	290–460 nm
Stack emissions	UV absorption	NO, NH3, SO2	190–320 nm
Soil	NIR reflectance	Moisture, organic matter, clay, carbonate	1000–2500 nm
Vegetation	Vis-NIR reflectance	Chlorophyll, red edge, canopy water	400–1000 nm
Plastics sorting	NIR reflectance	Polymer type	900–1700 nm

Evolve Sensing for environmental monitoring

• SmartEngine: UV-Vis-NIR platform for water and air measurements.
• SideWinder: InGaAs NIR for soil, moisture and polymer sorting.
• DS Series: two spectrometers on a common trigger for UV through NIR coverage in one instrument.
• Low-power USB operation for battery and field deployments, with SDK support for data loggers.

We are happy to help configure a spectrometer for a field or process installation.