To study the influence of polluted air-mass transport carrying ozone (O3) and black carbon (BC) in the high Himalayas, since March 2006 the Nepal Climate Observatory at Pyramid (NCO-P) GAW-WMO global station (N...To study the influence of polluted air-mass transport carrying ozone (O3) and black carbon (BC) in the high Himalayas, since March 2006 the Nepal Climate Observatory at Pyramid (NCO-P) GAW-WMO global station (Nepal, 5079 m a.s.l.) is operative. During the first 5-year measurements, the O3 and BC concentrations have shown a mean value of 48 ± 12 ppb (± standard deviation) and 208 ± 374 ng/m3, respectively. Both O3 and BC showed well defined seasonal cycles with maxima during pre-monsoon (O3 : 61.3 ± 7.7 ppbV; BC: 444 ± 433 ng/m3) and minima during the summer monsoon (O3 : 40.1 ± 12.4 ppbV; BC: 64 ± 101 ng/m3). The analysis of the days characterised by the presence of a significant BC increase with respect to the typical seasonal cycle identified 156 days affected by "acute" pollution events, corresponding to 9.1% of the entire data-set. Such events mostly occur in the pre-monsoon period, when the O3 diurnal variability is strongly related to the transport of polluted air-mass rich on BC. On average, these "acute" pollution events were characterised by dramatic increases of BC (352%) and O3 (29%) levels compared with the remaining days.展开更多
The massive reductions in anthropogenic emissions resulting from the COVID-19 lockdown provided a unique opportunity to evaluate the effect of mitigation measures aiming to abate air pollution.In Mexico,the total lock...The massive reductions in anthropogenic emissions resulting from the COVID-19 lockdown provided a unique opportunity to evaluate the effect of mitigation measures aiming to abate air pollution.In Mexico,the total lockdown period took place during the dry-hot season when biomass burning activity is enhanced.Here,we investigate the role of biomass burning emissions on regional ozone levels in the Megalopolis of Central Mexico.The studied period covers the lockdown phases 2 and 3,and the first month of the New Normal.We applied a factor separation technique and process analysis to estimate the pure and synergistic contributions of emission reductions under lockdown and that from biomass burning to daily ozone maximum concentrations in 7 metropolitan areas of different states in the Megalopolis.The results revealed that biomass burning plumes likely masked the effect of massive reductions from mobile emissions,impacted the PBL development during phase 3 and favored transition and mixed NO_(x)-limited and VOC-limited regional regimes.This contributed to increased ozone production in the middle to lower PBL by changing the regional background levels which potentially could bias high ozone production efficiency estimations.Given the Megalopolis contribution to economic and societal development at national scale,our study suggests that ozone mitigation measures during the dry-hot season targeting mainly mobile emissions will likely be offset by biomass burning plumes.A regional and synergic policy aiming to control biomass burning would help to reduce the occurrence of high ozone levels in Central Mexico with the co-benefit of tackling short-lived climate pollutants.展开更多
文摘To study the influence of polluted air-mass transport carrying ozone (O3) and black carbon (BC) in the high Himalayas, since March 2006 the Nepal Climate Observatory at Pyramid (NCO-P) GAW-WMO global station (Nepal, 5079 m a.s.l.) is operative. During the first 5-year measurements, the O3 and BC concentrations have shown a mean value of 48 ± 12 ppb (± standard deviation) and 208 ± 374 ng/m3, respectively. Both O3 and BC showed well defined seasonal cycles with maxima during pre-monsoon (O3 : 61.3 ± 7.7 ppbV; BC: 444 ± 433 ng/m3) and minima during the summer monsoon (O3 : 40.1 ± 12.4 ppbV; BC: 64 ± 101 ng/m3). The analysis of the days characterised by the presence of a significant BC increase with respect to the typical seasonal cycle identified 156 days affected by "acute" pollution events, corresponding to 9.1% of the entire data-set. Such events mostly occur in the pre-monsoon period, when the O3 diurnal variability is strongly related to the transport of polluted air-mass rich on BC. On average, these "acute" pollution events were characterised by dramatic increases of BC (352%) and O3 (29%) levels compared with the remaining days.
文摘The massive reductions in anthropogenic emissions resulting from the COVID-19 lockdown provided a unique opportunity to evaluate the effect of mitigation measures aiming to abate air pollution.In Mexico,the total lockdown period took place during the dry-hot season when biomass burning activity is enhanced.Here,we investigate the role of biomass burning emissions on regional ozone levels in the Megalopolis of Central Mexico.The studied period covers the lockdown phases 2 and 3,and the first month of the New Normal.We applied a factor separation technique and process analysis to estimate the pure and synergistic contributions of emission reductions under lockdown and that from biomass burning to daily ozone maximum concentrations in 7 metropolitan areas of different states in the Megalopolis.The results revealed that biomass burning plumes likely masked the effect of massive reductions from mobile emissions,impacted the PBL development during phase 3 and favored transition and mixed NO_(x)-limited and VOC-limited regional regimes.This contributed to increased ozone production in the middle to lower PBL by changing the regional background levels which potentially could bias high ozone production efficiency estimations.Given the Megalopolis contribution to economic and societal development at national scale,our study suggests that ozone mitigation measures during the dry-hot season targeting mainly mobile emissions will likely be offset by biomass burning plumes.A regional and synergic policy aiming to control biomass burning would help to reduce the occurrence of high ozone levels in Central Mexico with the co-benefit of tackling short-lived climate pollutants.