Use of airborne PM 10 concentrations at air quality monitoring sites in Imperial County, California, as an indication of geographical influences on lung health during drought periods: a time-series analysis
Authors: Aubrey Doede, Robert Davis
Journal: The Lancet Planetary Health (2018)

Background2012–16 marked the worst drought in California, USA, in more than a century. Droughts are expected to recur in broader areas as a result of anthropogenic climate change. The Salton Sea, a landlocked depression without natural river inflow, is almost entirely dependent on agricultural irrigation of Imperial Valley's 475 000 acres of farmland, although its water level has been diminishing because of decreased precipitation and river flow. Exposure of the lakebed and ground heating in an already arid climate might cause an increase in airborne PM10 (particulate matter less than 10 μm in diameter), reactive nitrogen, and ground-level ozone, exacerbating asthma symptoms. During the most severe drought years, admissions of children to the emergency department for asthma-related symptoms in Imperial County were among the highest in California and double the number for the entire state. However, previous analyses have not taken into account environmental mediators with more specific geographical granularity than the county level.MethodsIn this analysis, we used 2006–16 data from the US Drought Monitor and the five air quality monitoring stations (AQMS) within Imperial County, CA, USA. To reconcile sampling differences between 7-day drought severity reports and 6-day PM10 measurements, a date windowing function was applied to match each PM10 measurement to the drought severity value at the most closely related point in absolute time. Upon visually examining the data, lower concentrations of PM10 appeared to drive the correlation between AQMS. Therefore, in two time series—all years and non-drought years only—all concentrations of PM10 that were lower than 75 ppm were removed, and the remaining concentrations were used to measure correlations between AQMS.FindingsPM10 concentrations across all years were poorly correlated between AQMS (r=0·41–0·80; p<0·05). When removing PM10 concentrations lower than 75 ppm and examining only the remaining values, the correlation coefficients for these values decreased (r=0·16–0·53; p<0·05). When removing drought years (2012 onwards), these values were slightly more correlated in comparisons between some AQMS than across all observed years (r=0·46–0·77; p<0·05).InterpretationThe inconsistency in PM10 concentrations between AQMS on high PM10 days and during drought years suggests that different AQMS do not experience the same changes in air quality, particularly on days most likely to cause asthma exacerbations. This finding indicates a geographical component of air-quality differences and the potential for children near rural farmland to be more susceptible to asthma and lung disease. Future research regarding respiratory health in drought areas will provide a perspective on under-represented local and regional environmental challenges. Drought is one of the most expensive natural events from a number of economic and public health stances, and findings in support of the health implications of agriculture and water use have broader potential implications for water policy, drought mitigation strategies, and health improvement.FundingNone.