Increasing ozone in marine boundary layer inflow at the west coasts of North America and Europe

Abstract

Abstract. An effective method is presented for determining the ozone (O 3 ) mixing ratio in the onshore flow of marine air at the North American west coast. By combining the data available from all marine boundary layer (MBL) sites with simultaneous wind data, decadal temporal trends of MBL O 3 in all seasons are established with high precision. The average springtime temporal trend over the past two decades is 0.46 ppbv/yr with a 95% confidence limit of 0.13 ppbv/yr, and statistically significant trends are found for all seasons except autumn, which does have a significantly smaller trend than other seasons. The average trend in mean annual ozone is 0.34±0.09 ppbv/yr. These decadal trends at the North American west coast present a striking comparison and contrast with the trends reported for the European west coast at Mace Head, Ireland. The trends in the winter, spring and summer seasons compare well at the two locations, while the Mace Head trend is significantly greater in autumn. Even though the trends are similar, the absolute O 3 mixing ratios differ markedly, with the marine air arriving at Europe in all seasons containing 7±2 ppbv higher ozone than marine air arriving at North America. Further, the ozone mixing ratios at the North American west coast show no indication of stabilizing as has been reported for Mace Head. In a larger historical context the background boundary layer O 3 mixing ratios over the 130 years covered by available data have increased substantially (by a factor of two to three), and this increase continues at present, at least in the MBL of the Pacific coast region of North America. The reproduction of the increasing trends in MBL O 3 over the past two decades, as well as the difference in the O 3 mixing ratios between the Correspondence to: D. D. Parrish (david.d.parrish@noaa.gov) two coastal regions will present a significant challenge for global chemical transport models. Further, the ability of the models to at least semi-quantitatively reproduce the longerterm, historical trends may an even greater challenge.

Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006

“…Jaffe and Ray (2007) have examined 20 years of data (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) and found an average increase of 0.26 ppbv/year of O 3 . Parrish et al (2009) have found a similar trend from looking at west coast marine boundary layer sites (0.34 ppbv/year). Chan and Vet (2010) used a muti-site cluster analysis and also found a significant upward trend in background ozone along the west coast of North America.…”

Free tropospheric peroxyacetyl nitrate (PAN) and ozone at Mount Bachelor: potential causes of variability and timescale for trend detection

“…Several previous analyses of O 3 and PAN trends have used data from multiple sites with complex data segregation schemes. This was done due to the fact that no single site existed in this region with long term data (Parrish et al, , 2009Cooper et al, 2010). Our analysis suggests that if the true O 3 trend over western North America due to rising Asian precursor emissions is on the order of 1 % per year, it could be corroborated at a site like MBO in a relatively short timeframe with a direct analysis of mean O 3 concentrations.…”

“…They used a retroplume analysis to show that the rate of increase in O 3 mixing ratios is greatest in air masses directly transported from Asia. Parrish et al (2009) also showed a positive trend (0.46 ppbv year −1 ) in springtime onshore flow of marine air along the North American west coast. However O 3 concentrations above the boundary layer (BL) at Trinidad Head, California do not show a significant change over the last 10 years (Oltmans et al, 2008).…”

“…There are multiple lines of evidence that springtime O 3 concentrations are increasing over western North America Chan and Vet, 2010;Parrish et al, 2009;Jaffe et al, 2003;Jaffe and Ray, 2007;NRC, 2010;Parrish et al, 2004). The most recent analysis by Cooper et al (2010) showed a strong increase in lower free tropospheric (FT) springtime O 3 mixing ratios from 1995 to 2008.…”

Characteristics of Summertime Volatile Organic Compounds in the Lower Free Troposphere: Background Measurements at Mt. Fuji

“…Air pollutants such as ozone released in the boundary layer of East Asia are sent into free troposphere predominately through the process of frontal lifting (Liu et al, 2003). The increased ozone in East Asia can therefore be rapidly spread over the northern Pacific (Hoell et al, 1997;Zhang et al, 2008) and transport to North America (Jaffe et al, 1999;Parrish et al, 2009;Cooper et al, 2010;Verstraeten et al, 2015;Lin et al, 2017). A deeper understanding of the characteristics of VOCs and photochemical mechanisms underlying the Asian continental outflow can be gained by obtaining measurements on the rim of the western Pacific.…”