دانلود رایگان مقاله انگلیسی روند هیدروکلراید استراتوسفر از ماموریت ماهواره ای ACE - الزویر 2018

abstract

The Montreal Protocol has banned the production of long-lived chlorine-containing gases such as chlorofluorocarbons (CFCs) that deplete stratospheric ozone. These halogenated compounds ultimately form HCl in the upper atmosphere; the effectiveness of the Montreal Protocol can therefore be monitored by measuring stratospheric HCl. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measures infrared solar occultation spectra of the Earth’s atmosphere from which altitude profiles of HCl volume mixing ratios (VMRs) are determined. The upper stratospheric HCl VMR time series has a linear trend of −4.8 ± 0.2%/decade for 2004–2017, highlighting the continuing success of the Montreal Protocol.

3. Discussion and conclusion

The stratospheric trend value reported in the 2014 WMO ozone report [12] for 1997–2013 was −5.9 ± 1.5%/decade based on merged HALOE and ACE-FTS data. For 2004–2010, Brown et al. [11] reported a trend value of −7 ± 1%/decade from ACE-FTS and −6 ± 1%/decade from the SLIMCAT model. GOZCARDS [10] shows similar trend values but reports that recent values are decreasing in magnitude. Using N2O in the model gives comparable ACE-FTS (30–60°N) HCl trend values in the lower stratosphere as the values derived by Stolarski et al. [14] for 45–50°N, e.g., at 15 hPa the MLS value is −3.6 ± 1.5%/decade compared to the ACE-FTS value of −5.0 ± 0.4%/decade. There is also strong evidence in ACE data (Fig. 1) for a change in slope since about 2010. For example, at 0.68 hPa the 2004–2010 linear trend is −5.9 ± 0.5%/decade and from 2011 to 2017 the value is −4.1 ± 0.4%/decade, with an overall 2004–2017 linear trend of −4.8 ± 0.2%/decade. Also plotted in Fig. 1 is the total effective tropospheric chlorine [18] lagged by 4 years to account for the transport time to the upper stratosphere. There is an excellent correlation (r = 0.86) between the two curves. The trend values for total tropospheric chlorine in Fig. 1 are −5.8 ± 0.1%/decade for 2004– 2010 and −4.0 ± 0.1%/decade for 2010–2017 in excellent agreement with ACE values. The change in slope at 2010 is due to the rapid initial decline of species with shorter atmospheric lifetimes such as methyl chloroform (https://www.esrl.noaa.gov/gmd/odgi/). The total column density trend values for 2000–2009 from 16 NDACC sites show considerable variability, but the simple average over all sites is −8%/decade [3]. A more recent NDACC value for the total Cly column trend (dominated by HCl) for 1997–2016 is reported as −5.0 ± 1.5%/decade [19], in agreement with the ACE trend. ACE HCl stratospheric trend values are therefore in agreement with other measurements and are correlated with tropospheric total chlorine abundances. The conclusion from the updated ACE HCl trends is that the Montreal Protocol has been and continues to be successful. Upper stratospheric HCl VMR profile values are declining at an average rate of −4.8 ± 0.2%/decade for 2004–2017.