Integrating Nephelometer The Ecotech Aurora 3000 Integrating Nephelometer measures both aerosol total (σsp) and back (σb) scattering coefficients at three wavelengths: 450 nm (blue), 525 nm (green) and 635 nm (red). The scattering coefficient measurements (light scattering angle sampled: 10° – 170°) are combined with backscatter measurements (light backscattering angle sampled: 90° - 170°). Forward scatter can be calculated from subtracting backscatter from total scatter. The measured values are adjusted automatically and in real-time by on-board temperature and pressure sensors. The dimension of σsp are inverse length (inverse megameters Mm-1) and the instrument measurement range goes from <0.25 to 2000 Mm-1. At Chacaltaya, data is stored every minute. Zero checks are performed every 3 months.