A method comprising: directing light from at least one light source through a gas sample, the at least one light source including a tunable diode laser, a tunable quantum cascade semiconductor laser, a tunable horizontal cavity laser, a tunable vertical cavity surface emitting semiconductor laser, or a means for nonlinear frequency generation of tunable light, the light from the at least one light source comprising a target wavelength and a reference wavelength; quantifying a target analyte absorption of light in the gas sample at the target wavelength and a background reference analyte absorption of light in the gas sample at the reference wavelength, the gas sample comprising the target analyte and a background reference analyte, the target analyte having a resolvable target spectral feature at the target wavelength, the background reference analyte having a resolvable background spectral feature at the reference wavelength, that is relatively free of interfering absorption features of other components in the gas sample, and also an interfering background spectral feature at the target wavelength, wherein the at least one light source provides a light beam having a spectrally narrower emission band width than the target analyte absorption and the background reference analyte absorption; calculating an inferred background reference analyte absorption of the background reference analyte at the target wavelength using a background gas adjustment factor that relates the quantified reference absorption at the reference wavelength to light absorption quantified at the target wavelength that is due to the background reference analyte; and calculating a target analyte concentration in the gas sample by adjusting the target absorption using the inferred background reference analyte absorption to determine a calculated target analyte absorption at the target wavelength. directing light from at least one light source through a gas sample, the at least one light source including a tunable diode laser, a tunable quantum cascade semiconductor laser, a tunable horizontal cavity laser, a tunable vertical cavity surface emitting semiconductor laser, or a means for nonlinear frequency generation of tunable light, the light from the at least one light source comprising a target wavelength and a reference wavelength; quantifying a target analyte absorption of light in the gas sample at the target wavelength and a background reference analyte absorption of light in the gas sample at the reference wavelength, the gas sample comprising the target analyte and a background reference analyte, the target analyte having a resolvable target spectral feature at the target wavelength, the background reference analyte having a resolvable background spectral feature at the reference wavelength, that is relatively free of interfering absorption features of other components in the gas sample, and also an interfering background spectral feature at the target wavelength, wherein the at least one light source provides a light beam having a spectrally narrower emission band width than the target analyte absorption and the background reference analyte absorption; calculating an inferred background reference analyte absorption of the background reference analyte at the target wavelength using a background gas adjustment factor that relates the quantified reference absorption at the reference wavelength to light absorption quantified at the target wavelength that is due to the background reference analyte; and calculating a target analyte concentration in the gas sample by adjusting the target absorption using the inferred background reference analyte absorption to determine a calculated target analyte absorption at the target wavelength. <EOS>