Variation in Sunshine Duration and Related Aerosol Influences at Shangdianzi GAW Station, China: 1958–2021

Sunshine duration(SD) is adopted widely to study global dimming/brightening. However, long-term simultaneous measurements of SD and closely related impact factors require further analysis to elucidate how and why SD has varied during the past decades. In this study, a long-term(1958–2021) SD data series obtained from the Shangdianzi Global Atmosphere Watch(GAW) station in China was analyzed to detect linear trends, climatic jumps, and climatic periods in SD using linear fitting, the Mann–Kendall trend test, and the continuous wavelet transform method. Annual SD exhibited steady dimming(-67.3 h decade-1) before 2010, followed by a period of brightening(189.9 h decade-1)during 2011–2020. An abrupt jump in annual SD occurred in 1995, and the annual SD anomaly exhibited significant oscillation with ~3-yr periodicity during 1960–1978. Partial least squares analysis revealed that annual SD anomaly was associated with variations in relative humidity, gale days, cloud cover, and black carbon(BC). Further analysis of the clear-sky daily sunshine percentage(DSP) and simultaneous measurements of aerosol properties, including aerosol optical depth, aerosol extinction coefficient, single scattering albedo(SSA), BC, and total suspended particulates, suggested that variation in DSP was affected primarily by aerosol scattering and absorption. Furthermore, the hourly clear-sky SD at high aerosol loading was approximately 60% and 56% of that at middle and low aerosol loadings, respectively. The pattern of diurnal variation in clear-sky hourly SD, as well as the actual values, can be affected by the fine particulate concentration, aerosol extinction coefficient, and SSA.

A study of peroxyacetyl nitrate at a rural site in Beijing based on continuous observations from 2015 to 2019 and the WRFChem model

Peroxyacetyl nitrate(PA N)is one of the most important photochemical pollutants and has aroused much concern in China in recent decades.However,few studies described the long-term variations in PAN in China.In this study,we continuously monitored the PAN,03 and NOx concentrations at a regional background site near Beijing from August 2015 to February 2019.Based on the observed concentrations and climate data,w e analyzed the seasonal PAN variations.The results revealed that the monthly mean PAN concentration ranged from 0.33-2.41 ppb,with an average value of 0.94 ppb.The PAN concentration exhibited a distinct seasonal variation,with high values in spring and low values in winter.After analyzing the corresponding meteorological data,we found that stronger ultraviolet(UV)radiation,a relatively longer lifetime and a higher background PAN concentration contributed to the high PAN concentrations in spring.In addition,with the utilization of the WRF-Chem(Weather Research and Forecasting with Chemistry)model,the cause of the extremely high PAN concentration in spring 2018 wa s determined.The model results demonstrated that an anomalously low pressure and the southwesterly winds in northern China might be the main causes of the increased PAN concentration in Beijing and its surrounding area in spring 2018.