Abstract
Abstract. In May 2016, the Horse River wildfire led to the evacuation of ∼ 88 000 people from Fort McMurray and surrounding areas and consumed ∼ 590 000 ha of land in Northern Alberta and Saskatchewan. Within the plume, satellite instruments measured elevated values of CO, NH3, and NO2. CO was measured by two Infrared Atmospheric Sounding Interferometers (IASI-A and IASI-B), NH3 by IASI-A, IASI-B, and the Cross-track Infrared Sounder (CrIS), and NO2 by the Ozone Monitoring Instrument (OMI). Daily emission rates were calculated from the satellite measurements using fire hotspot information from the Moderate Resolution Imaging Spectroradiometer (MODIS) and wind information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis, combined with assumptions on lifetimes and the altitude range of the plume. Sensitivity tests were performed and it was found that uncertainties of emission estimates are more sensitive to the plume shape for CO and to the lifetime for NH3 and NOx. The satellite-derived emission rates were ∼ 50–300 kt d−1 for CO, ∼ 1–7 kt d−1 for NH3, and ∼ 0.5–2 kt d−1 for NOx (expressed as NO) during the most active fire periods. The daily satellite-derived emission estimates were found to correlate fairly well (R∼0.4–0.7) with daily output from the ECMWF Global Fire Assimilation System (GFAS) and the Environment and Climate Change Canada (ECCC) FireWork models, with agreement within a factor of 2 for most comparisons. Emission ratios of NH3∕CO, NOx∕CO, and NOx∕NH3 were calculated and compared against enhancement ratios of surface concentrations measured at permanent surface air monitoring stations and by the Alberta Environment and Parks Mobile Air Monitoring Laboratory (MAML). For NH3∕CO, the satellite emission ratios of ∼ 0.02 are within a factor of 2 of the model emission ratios and surface enhancement ratios. For NOx∕CO satellite-measured emission ratios of ∼0.01 are lower than the modelled emission ratios of 0.033 for GFAS and 0.014 for FireWork, but are larger than the surface enhancement ratios of ∼0.003, which may have been affected by the short lifetime of NOx. Total emissions from the Horse River fire for May 2016 were calculated and compared against total annual anthropogenic emissions for the province of Alberta in 2016 from the ECCC Air Pollutant Emissions Inventory (APEI). Satellite-measured emissions of CO are ∼1500 kt for the Horse River fire and exceed the total annual Alberta anthropogenic CO emissions of 992.6 kt for 2016. The satellite-measured emissions during the Horse River fire of ∼30 kt of NH3 and ∼7 kt of NOx (expressed as NO) are approximately 20 % and 1 % of the magnitude of total annual Alberta anthropogenic emissions, respectively.
Highlights
The 2016 Horse River wildfire (MNP LLP, 2017) was first observed on 1 May 2016 approximately 7 km south-west of Fort McMurray and grew rapidly
The Cross-track Infrared Sounder (CrIS) instrument is flown on-board the Suomi National Polar-orbiting Partnership (S-NPP) satellite with an overpass of ∼ 01:30 and 13:30 local solar time (LST) and a pixel spatial resolution of 14 km circles at nadir
Several other days appeared cloud-free despite a large reported cloud radiative fraction (CRF) in pixels that contained smoke plumes. This suggests that the smoke itself was being identified as cloud. On these days, the CRF was set to zero for large NO2 vertical column densities (VCDs) (> 1 ×1015 molec cm−2) and the Ozone Monitoring Instrument (OMI) air mass factors (AMFs) were modified to account for the effect of the smoke plume on the NO2 VCDs
Summary
The 2016 Horse River wildfire (MNP LLP, 2017) was first observed on 1 May 2016 approximately 7 km south-west of Fort McMurray and grew rapidly. Akagi et al (2011) estimated variability in boreal forest emission factors from aircraft and laboratory studies of 35 % for CO, 85 % for NH3, and 77 % for NOx. A study in north-western Alberta found that deciduous trees (e.g., trembling aspen) contain more nitrogen than conifers (e.g., white spruce) (Jerabkova et al, 2006); this might be expected to lead to larger emissions of NOx and NH3 for trembling aspen. Due to the close proximity of the fire to industry and communities, there is a relatively extensive surface monitoring network in the region, and many surface air quality datasets are collected routinely in the area These networks captured detailed information about the wildfire plume (Landis et al, 2018; Wentworth et al, 2018), which can be used to support the satellite-based estimates. We compare emission estimates with model data, explore relationships between CO, NH3, and NOx, and derive emission factors from the satellite data
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