Tower-based profiles of wintertime secondary organic aerosols in the urban boundary layer over Guangzhou.

Secondary organic aerosol (SOA) accounts for a large fraction of fine particulate matter (PM2.5), but the lack of vertical observations of SOA in the urban boundary layer (UBL) limits a comprehensive understanding of its sources and formation mechanisms. In this study, PM2.5 samples were simultaneously collected at 3 m, 118 m, and 488 m on the Canton Tower in Guangzhou during winter. Typical SOA tracers, including oxidation products of isoprene (SOAI), monoterpene (SOAM), sesquiterpene (SOAS), and toluene (ASOA), were investigated alongside meteorological parameters and gaseous/particulate pollutants. Total concentrations of SOA tracers showed an increasing trend with height, with daytime levels exceeding nighttime levels. C5-alkene triols and 2-methylglyceric acid displayed a significant increase with height, potentially affected by nighttime chemistry in the residual layer, determining the overall vertical trend of SOAI tracers. Concentrations of later-generation SOAM (SOAM_S) tracers also increased with height, while those of first-generation SOAM (SOAM_F) tracers decreased, indicating relatively aged SOAM in the upper layers. SOAS and ASOA tracers exhibited higher enhancement under polluted conditions, likely impacted by biomass burning and anthropogenic emissions. The yields of SOAI tracers varied with temperature in the vertical profile. The formation of SOAM_F tracers was negatively correlated with relative humidity, liquid water content, and pH, affecting their vertical distributions. The effect of O3 on SOA formation enhanced significantly with height, influenced by air mass transport, and likely contributed to the higher yields of SOA in the upper layer. However, at ground level, SOA formation was primarily driven by high local emissions of both NOx and volatile organic compounds. We also observed the roles of SO2 in SOA generation, particularly at 118 m. This study demonstrates the vertical diurnal characteristics of SOA tracers in the UBL, highlighting the varying effects of meteorological conditions and anthropogenic pollutants on SOA formation at different heights.

Physiological and molecular response and tolerance of Macleaya cordata to lead toxicity.

BACKGROUND: Macleaya cordata is a traditional medicinal herb, and it has high tolerance and accumulation ability to heavy metals, which make it a good candidate species for studying phytoremediation. The objectives of this study were to investigate response and tolerance of M. cordata to lead (Pb) toxicity based on comparative analysis of transcriptome and proteome. RESULTS: In this study, the seedlings of M. cordata cultured in Hoagland solution were treated with 100 µmol·L- 1 Pb for 1 day (Pb 1d) or 7 days (Pb 7d), subsequently leaves of M. cordata were taken for the determination of Pb accumulation and hydrogen peroxide production (H2O2), meanwhile a total number of 223 significantly differentially expressed genes (DEGs) and 296 differentially expressed proteins (DEPs) were screened between control and Pb treatments. The results showed leaves of M. cordata had a special mechanism to maintain Pb at an appropriate level. Firstly, some DEGs were iron (Fe) deficiency-induced transporters, for example, genes of vacuolar iron transporter and three ABC transporter I family numbers were upregulated by Pb, which can maintain Fe homeostasis in cytoplasm or chloroplast. In addition, five genes of calcium (Ca2+) binding proteins were downregulated in Pb 1d, which may regulate cytoplasmic Ca2+ concentration and H2O2 signaling pathway. On the other hand, the cysteine synthase upregulated, glutathione S-transferase downregulated and glutathione reductase downregulated in Pb 7d can cause reduced glutathione accumulation and decrease Pb detoxification in leaves. Furthermore, DEPs of eight chlorophyll a/b binding proteins, five ATPases and eight ribosomal proteins can play a pivotal role on chloroplast turnover and ATP metabolism. CONCLUSIONS: Our results suggest that the proteins involved in Fe homeostasis and chloroplast turnover in mesophyll cells may play key roles in tolerance of M. cordata to Pb. This study offers some novel insights into Pb tolerance mechanism of plants, and the potential valuable for environmental remediation of this important medicinal plant.

Oxidative Stress Response and Metal Transport in Roots of Macleaya cordata Exposed to Lead and Zinc.

Heavy metal pollution possesses potential hazards to plant, animal and human health, which has become the focus of recent attention. Hence, phytoremediation has been regarded as one of the most important remediation technologies for heavy-metal-contaminated soils. In this research, a dominant mine tailing plant, Macleaya cordata, was used as the experimental material to compare the metal transport and oxidative stress response in its roots under lead (Pb) and zinc (Zn) treatments. The result showed that Pb was mainly accumulated in the roots of M. cordata under the Pb treatment; less than 1% Pb was transported to the parts above. An analysis of the Zn content demonstrated a 39% accumulation in the shoots. The production of reactive oxygen species was detected using the in situ histological staining of roots, which showed that hydrogen peroxide in the root tips was observed to increase with the increase in both Pb and Zn concentrations. No significant superoxide anion changes were noted in the root tips under the Pb treatment. An analysis of the root enzyme activity showed that increase in NADPH oxidase activity can be responsible for the production of superoxide anions, subsequent the inhibition of root growth and decrease in antioxidant enzyme activities in the roots of M. cordata exposed to excess Zn. In total, this research provides evidence that the root of M. cordata has a high antioxidant capacity for Pb stress, so it can accumulate more Pb without oxidative damage. On the other hand, the Zn accumulated in the roots of M. cordata causes oxidative damage to the root tips, which can stimulate more Zn transport to the shoots to reduce the damage to the roots. This result will provide a basis for the application of M. cordata in the phytoremediation of soil polluted by Pb-Zn compounds.