Aerosol optical properties measurements by a CAPS single scattering albedo monitor: Comparisons between summer and winter in Beijing, China

Abstract

Aerosol optical properties were measured in Beijing in summer and winter using a state‐of‐the‐art cavity attenuated phase shift single scattering albedo monitor (CAPS PMssa) along with aerosol composition measurements by aerosol mass spectrometers and aethalometers. The SSA directly measured by the CAPS PMssa showed overall agreements with those derived from colocated measurements. However, substantial differences were observed during periods with low SSA values in both summer and winter, suggesting that interpretation of low SSA values needs to be cautious. The average (±σ) extinction coefficient (bext) and absorption coefficient (bap) were 336 (±343) Mm−1 and 44 (±41) Mm−1, respectively, during wintertime, which were approximately twice those observed in summer, while the average SSA was relatively similar, 0.86 (±0.06) and 0.85 (±0.04) in summer and winter, respectively. Further analysis showed that the variations in SSA can be approximately parameterized as a function of mass fraction of secondary particulate matter (fSPM), which is SSA = 0.74 + 0.19 × fSPM (fSPM > 0.3, r2 = 0.85). The contributions of aerosol species to extinction coefficients during the two seasons were also estimated. Our results showed that the light extinction was dominantly contributed by ammonium sulfate (30%) and secondary organic aerosol (22%) in summer, while organic aerosol was the largest contributor (51%) in winter. Consistently, SPM played the major role in visibility degradation in both seasons by contributing 70% of the total extinction.

Vertically-resolved Characteristics of Air Pollution during Two Severe Winter Haze Episodes in Urban Beijing, China

“…The SSA values were generally consistent with those observed in previous studies (Li et al, 2015c;Lee et al, 2007;Han et al, 2015a;Han et al, 2017), e.g., 0.85 -0.91 during the fall of 2014 (Han et al, 2015a) and 0.85 (±0.04) in the winter of 2015 (Han et al, 2017). We also observed slightly lower values at lower altitudes, indicating an enhanced BC absorption due to the influences of local emissions (Sun et al, 2015a;Sun et al, 2010).…”

The impact of aerosols on photolysis frequencies and ozone production in Beijing during the 4-year period 2012–2015

“…Studies in Los Angeles (Jacobson, 1998), Mexico City (Castro et al, 2001;Raga et al, 2001;Li et al, 2011), São Paulo (de Miranda et al, 2005), Houston (Flynn et al, 2010), Europe (Real and Sartelet, 2011), and Russia (Péré et al, 2015) have found that aerosols reduce ozone concentration by 5 %-30 % by attenuating photolysis frequencies. Studies in the eastern United States have shown that scattering aerosols increase ozone concentration by 5 %-60 % by increasing the photolysis frequencies (Dickerson et al, 1997;He and Carmichael, 1999). Therefore, it is necessary to quantitatively evaluate the effect of aerosols on photolysis frequencies for a better understanding of ozone formation under highly polluted conditions.…”

Vertical profiles of NO<sub>2</sub>, SO<sub>2</sub>, HONO, HCHO, CHOCHO and aerosols derived from MAX-DOAS measurements at a rural site in the central western North China Plain and their relation to emission sources and effects of regional transport

“…The existing profile inversion approaches for MAX-DOAS can be sorted into two groups: inversion algorithms based on the optimal estimation (OE) method and iterative approaches, e.g. the Gauß-Newton or Levenberg-Marquardt methods (Rodgers, 2000;Frieß et al, 2006Frieß et al, , 2011Wittrock, 2006;Irie et al, 2008Irie et al, , 2011Clémer et al, 2010;Yilmaz, 2012;Hartl and Wenig, 2013;Y. Wang et al, 2013a, b), and the so-called parameterized approaches using look-up tables (X.…”