Chemical and optical properties of smoke aerosol from the 1998 Mexico fires

Severe drought conditions in Mexico and Central America in 1998 led to numerous fires that Spring; heavy plumes of smoke were transported into the U.S. in April and May. The optical properties of the smoke-impacted aerosols were observed by in-situ airborne and ground-based Sun photometers. The haze was also sampled at long-term monitoring sites operated as part of the IMPROVE (Interagency Monitoring of Protected Visual Environments) network, and the chemical composition of the particulate matter was derived from these measurements. Both the optical and chemical data suggest that the smoke-impacted aerosols were more hygroscopic, with higher single-scattering albedos, than smoke aerosols observed closer to biomass burning sources. A model of the optical properties of the haze was developed that is consistent with optical properties of other smoke-impacted aerosols, taking into account variations in the aerosol hygroscopic and black carbon fractions. The model demonstrates the inter-dependency of the key optical parameters: particle size, single-scattering albedo and real refractive index.