Apportioning Smoke Impacts of 2018 Wildfires on Eastern Sierra Nevada Sites

Sean Mueller,Sean Raffuse,Susan O’Neill,Leland Tarnay

doi:10.3390/atmos11090970

Abstract

The summer of 2018 saw intense smoke impacts on the eastern side of the Sierra Nevada in California, which have been anecdotally ascribed to the closest wildfire, the Lions Fire. We examined the role of the Lions Fire and four other, simultaneous large wildfires on smoke impacts across the Eastern Sierra. Our approach combined GOES-16 satellite data with fire activity, fuel loading, and fuel type, to allocate emissions diurnally per hour for each fire. To apportion smoke impacts at key monitoring sites, dispersion was modeled via the BlueSky framework, and daily averaged PM2.5 concentrations were estimated from 23 July to 29 August 2018. To estimate the relative impact of each contributing wildfire at six Eastern Sierra monitoring sites, we layered the multiple modeled impacts, calculated their proportion from each fire and at each site, and used that proportion to apportion smoke from each fire’s monitored impact. The combined smoke concentration due to multiple large, concurrent, but more distant fires was on many days substantially higher than the concentration attributable to the Lions Fire, which was much closer to the air quality monitoring sites. These daily apportionments provide an objective basis for understanding the extent to which local versus regional fire affected Eastern Sierra Nevada air quality. The results corroborate previous case studies showing that slower-growing fires, when and where managed for resource objectives, can create more transient and manageable air quality impacts relative to larger fires where such management strategies are not used or feasible.

Highlights

In the United States, air quality has improved dramatically over the past four decades because of federal rules limiting emissions [1]
Such strategies align with air quality goals, because resource objectives require the kind of moderate fire behavior and slow growth that limit daily emissions, and limited daily emissions often result in limited smoke impacts downwind in all but the most direct or unfavorable dispersion scenarios
Relatively more transient when viewed across all Eastern Sierra monitoring sites within the study period, the Lions Fire impacts were more intense at the June Lake site

Summary

Introduction

In the United States, air quality has improved dramatically over the past four decades because of federal rules limiting emissions [1]. Wildfires contribute to high levels of air pollution and visibility impairment in the West, threatening to undo these air quality improvements [2]. They are expected to increase in frequency, size, and severity as the climate continues to change [3,4]. Smoke from wildland fires is a complex mixture that often varies spatially and temporally, and fine particulate matter (PM2.5 ) has been identified as the best single indicator of human health impacts [5,6,7]. Given the association between wildland fire smoke and public health [9,10], land management and regulatory agencies

Objectives

Methods

Results

Discussion

Conclusion