Reduced volatility of aerosols from surface emissions to the top of the planetary boundary layer

Abstract

Abstract. Aerosols from surface emission can be transported upwards through convective mixing in the planetary boundary layer (PBL), which subsequently interact with clouds, serving as important sources to nucleate droplets or ice particles. However, the evolution of aerosol composition during this vertical transport has yet to be explicitly understood. In this study, simultaneous measurements of detailed aerosol compositions were conducted at two sites, namely urban Beijing (50 m above sea level – a.s.l.) and Haituo mountain (1344 m a.s.l.) during wintertime, representing the anthropogenically polluted surface environment and the top of the PBL, respectively. The pollutants from surface emissions were observed to reach the mountain site on daily basis through daytime PBL convective mixing. From the surface to the top of PBL, we found efficient transport or formation of lower-volatility species (black carbon, sulfate, and low-volatile organic aerosol, OA); however, a notable reduction in semivolatile substances, such as the fractions of nitrate and semivolatile OA reduced by 74 % and 76 %, respectively, during the upward transport. This implies that the mass loss of these semivolatile species was driven by the evaporation process, which repartitioned the condensed semivolatile substances to the gas phase when aerosols were transported and exposed to a cleaner environment. In combination with the oxidation processes, these led to an enhanced oxidation state of OA at the top of the PBL compared to surface environment, with an increase of oxygen to carbon atomic ratio by 0.2. Such a reduction in aerosol volatility during vertical transport may be important in modifying its viscosity, nucleation activity, and atmospheric lifetime.

Enhanced formation of nitrogenous organic aerosols and brown carbon after aging in the planetary boundary layer

“…This, in turn, implied that there was a more important fraction of nitrogenous OA on the mountain than on the surface. The reduced fraction of inorganic nitrate, which has been reduced, is consistent with our previous study, which found that ammonium nitrate evaporated during vertical transport due to its higher volatility 28 .…”

“…Previous research has observed that surfaceemitted pollutants mix with the convective boundary layer during the day and reach mountainous sites on a daily basis. Effective transport or formation of low-volatile substances from the ground to the top of the PBL was observed; however, semi-volatile substances decreased during the upward transport process 28 .…”

Tracing the Formation of Secondary Aerosols Influenced by Solar Radiation and Relative Humidity in Suburban Environment

“…The enhanced solar radiation under C2 and C3 decreased the nitrate concentration with aging time, possibly due to the lack of NO x (Figure S9b in Supporting Information ). Higher temperature/lower RH or dilution during transport (Liu et al., 2021) may cause the evaporation of ammonium nitrate as nitric acid and ammonia in the gas phase due to its semi‐volatile nature (Aw & Kleeman, 2003; Liu et al., 2021). The aqueous‐phase process under high RH in C1 favored the partitioning of ammonium nitrate in the particulate phase.…”

Measurement report: On the contribution of long-distance transport to the secondary aerosol formation and aging

“…4). After transport, the fractional contribution of sulfate increased from 17 % (3.8 µg m −3 ) to 26 % (5.6 µg m −3 ) in the urban GZB transport pathway and from 20 % (6.2 µg m −3 ) to 32 % (9.9 µg m −3 ) in the BTH transport pathway, while the nitrate fraction increased from 12 % (2.7 µg m −3 ) to 19 % (3.7 µg m −3 ) in the urban GZB transport pathway but slightly decreased from 24 % (7.4 µg m −3 ) to 19 % (5.9 µg m −3 ) in the BTH transport pathway likely due to the mass loss of semi-volatile aerosol species (such as NH 4 NO 3 ) when aerosols are exposed to a cleaner environment during long-distance transport (Liu et al, 2021). We also compared the pollution episodes caused by the continuous transport from the BTH (EP1) and the urban GZB (EP2) (as shown in the shaded area in Fig.…”