Columnar Aerosol Optical Property Characterization and Aerosol Typing Based on Ground-Based Observations in a Rural Site in the Central Yangtze River Delta Region

Accurate and updated aerosol optical properties (AOPs) are of vital importance to climatology and environment-related studies for assessing the radiative impact of natural and anthropogenic aerosols. We comprehensively studied the columnar AOP observations between January 2019 and July 2020 from a ground-based remote sensing instrument located at a rural site operated by Central China Comprehensive Experimental Sites in the center of the Yangtze River Delta (YRD) region. In order to further study the aerosol type, two threshold-based aerosol classification methods were used to investigate the potential categories of aerosol particles under different aerosol loadings. Based on AOP observation and classification results, the potential relationships between the above-mentioned results and meteorological factors (i.e., humidity) and long-range transportation processes were analyzed. According to the results, obvious variation in aerosol optical depth (AOD) during the daytime, as well as throughout the year, was revealed. Investigation into AOD, single-scattering albedo (SSA), and absorption aerosol optical depth (AAOD) revealed the dominance of fine-mode aerosols with low absorptivity. According to the results of the two aerosol classification methods, the dominant aerosol types were continental (accounting for 43.9%, method A) and non-absorbing aerosols (62.5%, method B). Longer term columnar AOP observations using remote sensing alongside other techniques in the rural areas in East China are still needed for accurate parameterization in the future.

Measurement report: On the difference of aerosol hygroscopicity between high and low RH conditions in the North China Plain

Atmospheric processes, including both primary emissions and secondary formation, may exert complex effects on aerosol hygroscopicity, which is of significant importance in understanding and quantifying the effect of aerosols on climate and human health. In order to explore the influence of local emissions and secondary formation processes on aerosol hygroscopicity, we investigated the hygroscopic properties of submicron aerosol particles at a rural site in the North China Plain (NCP) in winter 2018. This was conducted by simultaneous measurements of aerosol hygroscopicity and chemical composition, using a self-assembled hygroscopic tandem differential mobility analyzer (HTDMA) and a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM). The hygroscopicity results showed that the particles during the entire campaign were mainly externally mixed, with a more hygroscopic (MH) mode and a less hygroscopic (LH) particles mode. The mean hygroscopicity parameter values (κmean) derived from hygroscopicity measurements for particles at 60, 100, 150, and 200 nm were 0.16, 0.18, 0.16, and 0.15, respectively. During this study, we classified two distinct episodes with different RH/T conditions, indicative of different primary emissions and secondary formation processes. It was observed that aerosols at all measured sizes were more hygroscopic under the high RH (HRH) episode than those under the low RH (LRH) episode. During the LRH, κ decreased with increasing particle size, which may be explained by the enhanced domestic heating at low temperature, causing large emissions of non- or less-hygroscopic primary aerosols. This is particularly obvious for 200 nm particles, with a dominant number fraction (> 50 %) of LH mode particles. Using O : C-dependent hygroscopic parameters of secondary organic compounds (κSOA), closure analysis between the HTDMA_measured κ and the ACSM_derived κ was carried out. The results showed that κSOA under the LRH episode was less sensitive to the changes in organic oxidation level, while κSOA under the HRH had a relatively stronger dependency on the organic O : C. This feature suggests that the different sources and aerosol evolution processes, partly resulting from the variation in atmospheric RH/T conditions, may lead to significant changes in aerosol chemical composition, which will further influence their corresponding physical properties.

Volatility Parameterization of Ambient Organic Aerosols at a rural site of the Northern China Plain

The volatility of organic aerosols plays a key role in determining their gas-particle partitioning, which subsequently alters the physicochemical properties and atmospheric fates of aerosol particles. Nevertheless, an accurate estimation of the volatility of organic aerosols (OA) remains challenging. Because most standard particulate organic compounds are scarce, on the other hand, their vapor pressures are too low to estimate by most traditional methods. Here, we deployed an iodide-adduct Long Time-of-Flight Chemical Ionization Mass Spectrometer (LToF-CIMS) coupled with a Filter Inlet for Gases and AEROsols (FIGAERO) to probe the relationship between the molecular formulas of atmospheric organic aerosol’s components and their volatilities. A number of Tmax (i.e., the temperature corresponding to the first signal peak of thermogram) were abstracted and validated from the desorption thermograms of mixed organic and inorganic calibrants which were atomized and then collected onto a Teflon filter. Besides, 30 filter samples of ambient air were collected in winter 2019 at Wangdu station in Beijing-Tianjin-Hebei region, and analyzed by FIGAERO-LToF-CIMS, leading to the identification of 1,448 compounds dominated by the CHO (containing carbon, hydrogen, and oxygen atoms) and CHON (containing carbon, hydrogen, oxygen, and nitrogen atoms) species. Among them, 181 organic formulas including 91 CHO and 90 CHON compounds were then selected since their thermograms can be characterized with clear Tmax values in more than 20 out of 30 filter samples and subsequently divided into two groups according to their O / C ratios. The mean O / C of these two groups are 0.56 ± 0.35 (average ± one standard deviation) and 0.18 ± 0.08, respectively. We then obtained the correlation functions between volatility and elemental composition for the two group compounds. Compared with previous volatility parameterizations, our correlation functions provide a better estimation of the volatility of semi-volatility organic compounds (SVOCs) and low-volatility organic compounds (LVOCs) in the ambient organic aerosols. Furthermore, we suggest that there should be specialized volatility parameterizations for different O / C organic compounds.

Urbanization and plant pathogen infection interact to affect the outcome of ecological interactions in an experimental multitrophic system

Urbanization can change interactions in insect communities, and the few studies of tritrophic interactions in urban settings focus on interactions between plants, herbivorous insects and their mutualists and natural enemies. Plant pathogen infection is also widespread and common, and infection may also alter such interactions, but we have no understanding of whether the ecological consequences of pathogen infection vary with urbanization. Using replicated aphid colonies on experimental plants, we investigated how infection by the plant pathogen Botrytis cinerea influences interactions between plants, aphids and the aphid natural enemies and ant mutualists in highly urbanized, suburban and rural study sites. Aphid and natural enemy abundance were highest in the suburban site, while mutualist ants were most abundant in the urban site, reversing the usual positive density-dependent relationship between natural enemies and aphids. The effect of pathogen infection varied with trait and site, mediated by natural enemy preference for hosts or prey on uninfected plants. The effect of infection on aphid abundance was only seen in the suburban site, where natural enemies were most abundant on uninfected plants and aphid numbers were greatest on infected plants. In the urban site, there was no effect of infection, while in the rural site, aphid numbers were lower on infected plants. Uninfected plants were smaller than infected plants and differed between locations. This study suggests that the effects of urbanization on ecological interactions may become more complex and difficult to predict as we study ecological assemblages and communities at greater levels of structural complexity.

SARS-CoV-2 seroprevalence in Kaduna State, Nigeria during October/November 2021, following three waves of infection and immediately prior to detection of the Omicron variant

Nigeria is the most populated country in Africa with an estimated ~213 million inhabitants. As of November 2021 there have been three waves of SARS-CoV-2 infection in Nigeria but there has been only one seroprevalence survey conducted to assess the proportion of a population that have been infected, which was performed in December 2020 after the first wave of infection. To provide an update on seroprevalence in Nigeria, we conducted survey at one urban site (n=400) and one rural site (n=402) in Kaduna State, Nigeria during October and November 2021 following the third wave of infection. Seroprevalence for the urban and rural sites was 42.5% and 53.5% respectively (mean 48.0%). Symptoms associated with seropositivity were identified for each site. The overall seroprevalence among unvaccinated individuals was 45.4%. The data indicates an infection rate in Kaduna State at least 387 times greater than that derived from cases confirmed by PCR. Extrapolating to the whole of Nigeria, it would suggest there has been at least 96.7 million infections (compared to 206,138 confirmed cases at the time of surveillance). The work presented here will inform public health policy and deployment strategies for testing, treatment, and vaccination in Nigeria, and provide a baseline for SARS-CoV-2 seroprevalence in Nigeria immediately prior to the spread of the Omicron variant.