Connections between summer air pollution and stagnation

Abstract

The body of literature on ambient air pollution suggests that atmospheric stagnation events trigger high levels of air pollution. In this paper we use fifteen years (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) of summertime in situ air quality measurements together with meteorological reanalysis data to examine the temporal correlation of pollutants with the Air Stagnation Index (ASI) on daily timescales. We find that while the direction of the relationship between the ASI and summertime PM 2.5 and O 3 ranges from near-zero to positive throughout regions comprising the contiguous United States (US), the strength of the relationship is very weak (e.g. in the Northeast the correlation coefficient between the ASI and PM 2.5 is 0.09). Moreover, similar to our analysis of the correlation of day-to-day variations of the ASI and pollutants, the percentage of co-occurring extreme pollution and stagnation events is small (e.g. days with a high coverage of stagnation only co-occur with extreme pollution events about one-third of the time in the Northeast). The southern US is an exception to our overall findings as the strength of the relationship between the ASI and pollution is stronger and the percentage of co-occurring events is higher compared with other regions. The results of this study suggest a reevaluation of the ASI as an index to assess meteorological and climatic impacts to air quality.

Disentangling the Drivers of the Summertime Ozone‐Temperature Relationship Over the United States

“…This results in a strong positive correlation coefficient ( r ( T ,O 3 ) = 0.67) and a high dO 3 /d T of 1.72 ppbv/K, both calculated using regionally averaged quantities. These results hold beyond the summer shown in Figure (Kerr & Waugh, ).…”

“…Differences between simulations are also examined in terms of the impact they have on days with extreme temperatures and O 3 concentrations. Similar to recent studies (e.g., Kerr & Waugh, 2018;Schnell & Prather, 2017;Sun et al, 2017), we define extremes in terms of exceedances above percentile thresholds. We adopt the 10th and 90th percentiles (P 10 and P 90 , respectively) as the thresholds for extreme O 3 and temperature events on both sides of the distributions, and we calculate the average O 3 concentration on days falling above (below) P 90 (P 10 ).…”

“…It is well known that high concentrations of surface‐level ozone (O 3 ) coincide with high temperatures (e.g., Bloomer et al, ; Kerr & Waugh, ; Schnell & Prather, ). This relationship is often quantified by the slope of the linear regression of O 3 versus temperature, herein referred to as “dO 3 /d T .” The observed dO 3 /d T in the United States generally ranges from 0–6 ppbv/K, with higher values found (1) in the northeastern compared with the southeastern United States (e.g., Brown‐Steiner et al, ; Rasmussen et al, ), (2) in urban regions (e.g., Sillman & Samson, ), and (3) during periods with higher anthropogenic nitrogen oxide (NO x ≡ NO + NO 2 ) emissions (e.g., Bloomer et al, ; Rasmussen et al, , ).…”

“…It is well known that high concentrations of surface-level ozone (O 3 ) coincide with high temperatures (e.g., Bloomer et al, 2009;Kerr & Waugh, 2018;Schnell & Prather, 2017). This relationship is often quantified by the slope of the linear regression of O 3 versus temperature, herein referred to as "dO 3 ∕dT."…”

Near-surface elevated pollution: what we don’t know doesn’t hurt? A numerical study over Mt. Carmel

“…Most air pollution assessments are based on surface data (e.g. Kerr andWaugh 2018, McLagan et al 2018) and do not refer to the elevated layers. This may be justified by the focus on population exposure.…”