Characterization of peroxyacetyl nitrate (PAN) under different PM2.5 concentration in wintertime at a North China rural site.

As a secondary pollutant of photochemical pollution, peroxyacetyl nitrate (PAN) has attracted a close attention. A four-month campaign was conducted at a rural site in North China Plain (NCP) including the measurement of PAN, O3, NOx, PM2.5, oxygenated volatile organic compounds (OVOCs), photolysis rate constants of NO2 and O3 and meteorological parameters to investigate the wintertime characterization of photochemistry from November 2018 to February 2019. The results showed that the maximum and mean values of PAN were 4.38 and 0.93 ± 0.67 ppbv during the campaign, respectively. The PAN under different PM2.5 concentrations from below 75 µg/m3 up to 250 µg/m3, showed different diurnal variation and formation rate. In the PM2.5 concentration range of above 250 µg/m3, PAN had the largest daily mean value of 0.64 ppbv and the fastest production rate of 0.33 ppbv/hr. From the perspective of PAN's production mechanism, the light intensity and precursors concentrations under different PM2.5 pollution levels indicated that there were sufficient light intensity and high volatile organic compounds (VOCs) and NOx precursors concentration even under severe pollution level to generate a large amount of PAN. Moreover, the bimodal staggering phenomenon of PAN and PM2.5 provided a basis that PAN might aggravate haze through secondary organic aerosols (SOA) formation.

Characterization, source apportionment, air/plant partitioning and cancer risk assessment of atmospheric PAHs measured with tree components and passive air sampler.

In this study, ambient air and olive tree components (leaf and branch) were simultaneously collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) to investigate their levels and accumulations, temporal variations, possible sources, air-plant partitioning and cancer risks for 12 months. During the sampling period, total of 14 PAH (∑14PAH) concentrations measured in the olive leaves (dissolved and particle phase) and braches (1- and 2-year-old) were 593 ± 472, 81 ± 67, 558 ± 273 and 316 ± 213 ng/g dry weight (DW), respectively. Similarly, the average ∑14PAH concentrations measured in the ambient air was found to be 15 ± 16 ng/m3. Generally, 4-, 5- and 6- ring PAHs were the dominant groups for all tree components, while 2- and 3-ring PAHs were predominant in the air samples. Ring distributions and molecular diagnosis ratios were employed to determine PAH sources in the sampling site. Petroleum and combustion-related sources were found to be important. The Pearson correlation coefficient was allowed to figure out the affinity between PAH levels in the sampling materials and meteorological factors. Temperature and mixing layer height were found to be effective factors on the concentrations. Atmospheric PAH levels were also predicted to employ a bark-air exchange model for determining the PAH movement direction. The predicted/measured ratios were above 1.0. This was probably due to utilizing the branch values rather than bark values in the model. Finally, the risk of cancer has been evaluated. The calculated cancer risks via inhalation were at low levels for adults and children.

Size-resolved effective density of submicron particles during summertime in the rural atmosphere of Beijing, China.

Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5g/cm3 for 50 to 350nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6g/cm3 for 150, 240, and 350nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth.

[Differences in PM2.5 Components Between Urban and Rural Sites During Heavy Haze Event in Northern Henan Province].

In recent years, the Beijing-Tianjin-Hebei region and its surrounding areas have experienced multiple haze pollution processes. Owing to the limitation of observational instruments, there has not been a comparative study of haze pollution between urban and rural areas in northern Henan province. A series of high-time-resolution instruments were used during a regional heavy pollution process (January 12-25, 2018) at two urban sites and three rural sites. The results showed that SO42-, NO-3, and NH+4 (SNA) were the components with the highest proportion in PM2.5 at the five sites during the haze event with a range of 53%-63%, of which nitrate was the most important, accounting for 24%-32%, followed by sulfate, ranging from 13%-17%. Compared with urban sites, rural sites were more affected by organic matter, especially at night. With the aggravation of pollution, the proportion of SNA increased, reaching 67% during periods of heavy pollution. When the area was affected by the air mass transported from the south, the proportion of NO-3 in PM2.5 increased, and when the area was affected by the air transport in the north, the proportions of SO42- and organic matter increased. Ammonium nitrate was the most important component that led to the decrease in atmospheric visibility during the haze process. Moreover, the contributions of ammonium nitrate and ammonium sulfate at the urban sites were higher than those at the rural sites. To summarize, there were significant differences in PM2.5 components between the urban and rural sites. Urban areas need to continue to strengthen the reduction in gaseous precursors, and rural areas need to pay attention to the sources of carbonaceous aerosol.

First long-term surface ozone variations at an agricultural site in the North China Plain: Evolution under changing meteorology and emissions.

Significant upward trends in surface ozone (O3) have been widely reported in China during recent years, especially during warm seasons in the North China Plain (NCP), exerting adverse environmental effects on human health and agriculture. Quantifying long-term O3 variations and their attributions helps to understand the causes of regional O3 pollution and to formulate according control strategy. In this study, we present long-term trends of O3 in the warm seasons (April-September) during 2006-2019 at an agricultural site in the NCP and investigate the relative contributions of meteorological and anthropogenic factors. Overall, the maximum daily 8-h average (MDA8) O3 exhibited a weak decreasing trend with large interannual variability. < 6 % of the observed trend could be explained by changes in meteorological conditions, while the remaining 94 % was attributed to anthropogenic impacts. However, the interannual variability of warm season MDA8 O3 was driven by both meteorology (36 ± 28 %) and anthropogenic factors (64 ± 27 %). Daily maximum temperature was the most essential factor affecting O3 variations, followed by ultraviolet radiation b (UVB) and boundary layer height (BLH), with rising temperature trends inducing O3 inclines throughout April to August, while UVB mainly influenced O3 during summer months. Under changes in emissions and air quality, warm season O3 production regime gradually shifted from dominantly VOCs-limited during 2006-2015 to NOx-limited afterwards. Relatively steady HCHO and remarkably rising NOx levels resulted in the fast decreasing MDA8 O3 (-2.87 ppb yr-1) during 2006-2012. Rapidly decreasing NOx, flat or slightly increasing HCHO promoted O3 increases during 2012-2015 (9.76 ppb yr-1). While afterwards, slow increases in HCHO and downwards fluctuating NOx led to decreases in MDA8 O3 (-4.97 ppb yr-1). Additionally, continuous warming trends might promote natural emissions of O3 precursors and magnify their impacts on agricultural O3 by inducing high variability, which would require even more anthropogenic reduction to compensate for.

Impact of livelihood capital and rural site conditions on livelihood resilience of farm households: evidence from contiguous poverty-stricken areas in China.

Farm households around the world are increasingly exposed to both external and internal shocks and stressors. Enhancing the resilience of farm households to frequent disturbances holds paramount importance in fostering the sustainability of their livelihoods and the revitalization of rural areas. Based on 1500 household samples from 14 contiguous poverty-stricken areas (CPSA) in China, this study explores the causal pathways between livelihood capitals of farm households and rural site conditions of rural communities, as well as quantifying their impacts on farm households' livelihood resilience using structural equation models. In particular, the livelihood resilience of farm households is measured based on the "Exposure-Sensitivity-Adaptability" framework. The results show that livelihood resilience is positively represented by exposure and adaptability, but is negatively correlated with sensitivity. Specifically, households with lower mean health and higher dependency ratio are more sensitive to risks, while exposure to agroforestry pests and diseases will lead farm households to diversify their livelihood activities and increase crop and livestock variety to enhance their adaptability. The livelihood capital of farm households has a significant positive effect on livelihood resilience (ß = 0.874, p < 0.001). Rural site conditions have both significant direct and indirect impacts on livelihood resilience, with the direct impact (ß = - 0.207, p < 0.05) being negative and a bit larger than the positive indirect impact (ß = 0.163, p < 0.05), as mediated by livelihood capital. The government should, therefore, invest more in health insurance, education and training, financial support, and infrastructure, and implement village planning to enhance both the quality of household livelihood capitals and rural site conditions in CPSA.

Formation pathway of secondary inorganic aerosol and its influencing factors in Northern China: Comparison between urban and rural sites.

Secondary inorganic aerosol, including sulfate, nitrate, and ammonium (SNA), is a significant source of PM2.5 during haze episodes in Northern China. A series of high-time-resolution instruments were used in collecting PM2.5 chemical components and gaseous pollutants during a regional heavy pollution process from January 12-25, 2018, at urban and rural sites. SNA, accounting for >50% of PM2.5 at both sites, had greater importance on haze formation. Gas-phase and N2O5 hydrolysis reactions were the main formation pathways of nitrate during the daytime and nighttime, respectively. The OH radical was the primary factor for gas-phase reactions. HONO photolysis played a more critical role in OH radical formation when O3 concentration decreased during the haze episode. N2O5 hydrolysis reaction was mainly affected by O3 and aerosol water content. High relative humidity, aerosol water content, and N2O5 concentrations at the urban site enhanced the hydrolysis reactions more than those at the rural site. The aqueous-phase reactions dominated the sulfate formation with the highest rate of transition metal ion catalytic and H2O2 oxidation reactions at the urban and rural sites, respectively. Elevated relative humidity and particle acidity at the urban site resulted in a higher formation rate of aqueous-phase sulfate than at the rural site. The gas-particle partition coefficient of NH3 had a negative correlation with the particle pH, and the presence of NH3 could promote the increase of SNA concentration. Thus, more attention should be paid to the differences in SNA formation between urban and rural regions when formulating air quality policies.