Seasonal Variations of CH_4 Emissions in the Yangtze River Delta Region of China Are Driven by Agricultural Activities

Developed regions of the world represent a major atmospheric methane(CH_4) source, but these regional emissions remain poorly constrained. The Yangtze River Delta(YRD) region of China is densely populated(about 16% of China's total population) and consists of large anthropogenic and natural CH_4 sources. Here, atmospheric CH_4 concentrations measured at a 70-m tall tower in the YRD are combined with a scale factor Bayesian inverse(SFBI) modeling approach to constrain seasonal variations in CH_4 emissions. Results indicate that in 2018 agricultural soils(AGS, rice production) were the main driver of seasonal variability in atmospheric CH_4 concentration. There was an underestimation of emissions from AGS in the a priori inventories(EDGAR—Emissions Database for Global Atmospheric Research v432 or v50), especially during the growing seasons. Posteriori CH_4 emissions from AGS accounted for 39%(4.58 Tg, EDGAR v432) to 47%(5.21 Tg, EDGAR v50) of the total CH_4 emissions. The posteriori natural emissions(including wetlands and water bodies) were1.21 Tg and 1.06 Tg, accounting for 10.1%(EDGAR v432) and 9.5%(EDGAR v50) of total emissions in the YRD in2018. Results show that the dominant factor for seasonal variations in atmospheric concentration in the YRD was AGS,followed by natural sources. In summer, AGS contributed 42%(EDGAR v432) to 64%(EDGAR v50) of the CH_4 concentration enhancement while natural sources only contributed about 10%(EDGAR v50) to 15%(EDGAR v432). In addition, the newer version of the EDGAR product(EDGAR v50) provided more reasonable seasonal distribution of CH_4 emissions from rice cultivation than the old version(EDGAR v432).     

Dynamic responses of atmospheric carbon dioxide concentration to global temperature changes between 1850 and 2010

Changes in Earth's temperature have significant impacts on the global carbon cycle that vary at different time scales, yet to quantify such impacts with a simple scheme is traditionally deemed difficult. Here, we show that, by incorporating a temperature sensitivity parameter(1.64 ppm yr~(-1) ?C~(-1)) into a simple linear carbon-cycle model, we can accurately characterize the dynamic responses of atmospheric carbon dioxide(CO_2) concentration to anthropogenic carbon emissions and global temperature changes between 1850 and 2010(r~2 0.96 and the root-mean-square error 1 ppm for the period from 1960onward). Analytical analysis also indicates that the multiplication of the parameter with the response time of the atmospheric carbon reservoir(～12 year) approximates the long-term temperature sensitivity of global atmospheric CO_2concentration(～15 ppm?C~(-1)), generally consistent with previous estimates based on reconstructed CO_2 and climate records over the Little Ice Age. Our results suggest that recent increases in global surface temperatures, which accelerate the release of carbon from the surface reservoirs into the atmosphere, have partially offset surface carbon uptakes enhanced by the elevated atmospheric CO_2 concentration and slowed the net rate of atmospheric CO_2 sequestration by global land and oceans by ～30%since the 1960 s. The linear modeling framework outlined in this paper thus provides a useful tool to diagnose the observed atmospheric CO_2 dynamics and monitor their future changes.     

Monitoring Carbon Dioxide from Space:Retrieval Algorithm and Flux Inversion Based on GOSAT Data and Using CarbonTracker-China

Monitoring atmospheric carbon dioxide(CO_2) from space-borne state-of-the-art hyperspectral instruments can provide a high precision global dataset to improve carbon flux estimation and reduce the uncertainty of climate projection. Here, we introduce a carbon flux inversion system for estimating carbon flux with satellite measurements under the support of "The Strategic Priority Research Program of the Chinese Academy of Sciences—Climate Change: Carbon Budget and Relevant Issues". The carbon flux inversion system is composed of two separate parts: the Institute of Atmospheric Physics Carbon Dioxide Retrieval Algorithm for Satellite Remote Sensing(IAPCAS), and Carbon Tracker-China(CT-China), developed at the Chinese Academy of Sciences. The Greenhouse gases Observing SATellite(GOSAT) measurements are used in the carbon flux inversion experiment. To improve the quality of the IAPCAS-GOSAT retrieval, we have developed a post-screening and bias correction method, resulting in 25%–30% of the data remaining after quality control. Based on these data, the seasonal variation of XCO_2(column-averaged CO_2dry-air mole fraction) is studied, and a strong relation with vegetation cover and population is identified. Then, the IAPCAS-GOSAT XCO_2 product is used in carbon flux estimation by CT-China. The net ecosystem CO_2 exchange is-0.34 Pg C yr~(-1)(±0.08 Pg C yr~(-1)), with a large error reduction of 84%, which is a significant improvement on the error reduction when compared with in situ-only inversion.     

Observed Trends in Extreme Temperature over the Klang Valley,Malaysia

This study investigates the recent extreme temperature trends across 19 stations in the Klang Valley, Malaysia, over the period 2006-16. Fourteen extreme index trends were analyzed using the Mann-Kendall non-parametric test, with Sen’s slope as a magnitude estimator. Generally, the annual daily mean temperature, daily mean maximum temperature, and daily mean minimum temperature in the Klang Valley increased significantly, by 0.07°C yr~(-1), 0.07°C yr~(-1)and 0.08°C yr~(-1),respectively. For the warm temperature indices, the results indicated a significant upward trend for the annual maximum of maximum temperature, by 0.09°C yr~(-1), and the annual maximum of minimum temperature, by 0.11°C yr~(-1). The results for the total number of warm days and warm nights showed significant increasing trends of 5.02 d yr~(-1)and 6.92 d yr~(-1),respectively. For the cold temperature indices, there were upward trends for the annual minimum of maximum temperature,by 0.09°C yr~(-1), and the annual minimum of minimum temperature, by 0.03°C yr~(-1), concurrent with the decreases in the total number cold days (TX10P), with-3.80 d yr~(-1), and cold nights (TN10P), with-4.33 d yr~(-1). The 34°C and 37°C summer days results showed significant upward trends of 4.10 d yr~(-1) and 0.25 d yr~(-1), respectively. Overall, these findings showed upward warming trends in the Klang Valley, with the minimum temperature rate increasing more than that of the maximum temperature, especially in urban areas.     

Constraining anthropogenic CH4 emissions in Nanjing and the Yangtze River Delta,China, using atmospheric CO2 and CH4 mixing ratios

Methane （CH4） emissions estimated with the Intergovernmental Panel on Climate Change （IPCC） inventory method at the city and regional scale are subject to large uncertainties.In this study,we determined the CH4：CO2 emissions ratio for both Nanjing and the Yangtze River Delta （YRD）,using the atmospheric CH4 and CO2 concentrations measured at a suburban site in Nanjing in the winter.The atmospheric estimate of the CH4：CO2 emissions ratio was in reasonable agreement with that calculated using the IPCC method for the YRD （within 20％）,but was 200％ greater for the municipality of Nanjing.The most likely reason for the discrepancy is that emissions from unmanaged landfills are omitted from the official statistics on garbage production.     

Two-Year Observation of Fossil Fuel Carbon Dioxide Spatial Distribution in Xi'an City

The need for atmospheric carbon dioxide(CO_2) reduction in the context of global warming is widely acknowledged by the global scientific community.Fossil fuel CO_2(CO_(2ff)) emissions occur mainly in cities,and can be monitored directly with radiocarbon(~(14) C).In this research,annual plants [Setaria viridis(L.) Beauv.] were collected from 26 sites in 2013 and2014 in the central urban district of Xi'an City.The △~(14)C content of the samples were analyzed using a 3 MV Accelerator Mass Spectrometer,and CO_(2ff) concentrations were calculated based on mass balance equations.The results showed that the CO_(2ff) mixing ratio ranged from 15.9 to 25.0 ppm(part per million,equivalent to μmol mol~(-1)),with an average of 20.5 ppm in 2013.The range of measured values became larger in 2014,from 13.9 ppm to 33.1 ppm,with an average of 23.5 ppm.The differences among the average CO_(2ff) concentrations between the central area and outer urban areas were not statistically significant.Although the year-to-year variation of the CO_(2ff) concentration was significant(P 0.01),there was a distinctly low CO_(2 ff) value observed in the northeast corner of the city.CO_(2 ff) emiissions from vehicle exhaust and residential sources appeared to be more significant than two thermal power plants,according to our observed CO_(2 ff) spatial distribution.The variation of pollution source transport recorded in our observations was likely controlled by southwesterly winds.These results could assist in the optimal placement of regional CO_2 monitoring stations,and benefit the local government in the implementation of efficient carbon emission reduction measures.     

First Global Carbon Dioxide Maps Produced from Tan Sat Measurements

正1.The need for global carbon monitoring from space and the Tan Sat mission Global warming is a major problem,for which carbon dioxide(CO_2 )is the main greenhouse gas involved in heating the troposphere.However,the poor availability of global CO_2 measurements makes it difficult to estimate CO_2 emissions accurately.Satellite measurements would be very helpful for understanding the global CO_2 flux distribution if the CO_2 column-averaged dry-air mole fraction(XCO_2 )could     

Methane and nitrous oxide emissions from three paddy rice based cultivation systems in Southwest China

To understand methane (CH4) and nitrous oxide (N2O) emissions from permanently flooded rice paddy fields and to develop mitigation options, a field experiment was conducted in situ for two years (from late 2002 to early 2005) in three rice-based cultivation systems, which are a permanently flooded rice field cultivated with a single time and followed by a non-rice season (PF), a rice-wheat rotation system (RW) and a rice-rapeseed rotation system (RR) in a hilly area in Southwest China. The results showed that the total CH4 emissions from PF were 646.3±52.1 and 215.0±45.4 kg CH4 hm-2 during the rice-growing period and non-rice period, respectively. Both values were much lower than many previous reports from similar regions in Southwest China. The CH4 emissions in the rice-growing season were more intensive in PF, as compared to RW and RR. Only 33% of the total annual CH4 emission in PF occurred in the non-rice season, though the duration of this season is two times longer than the rice season. The annual mean N2O flux in PF was 4.5±0.6 kg N2O hm-2 yr-1. The N2O emission in the rice-growing season was also more intensive than in the non-rice season, with only 16% of the total annual emission occurring in the non-rice season. The amounts of N2O emission in PF were ignorable compared to the CH4 emission in terms of the global warming potential (GWP). Changing PF to RW or RR not only eliminated CH4 emissions in the non-rice season, but also substantially reduced the CH4 emission during the following rice-growing period (ca. 58%, P<0.05). However, this change in cultivation system substantially increased N2O emissions, especially in the non-rice season, by a factor of 3.7 to 4.5. On the 100-year horizon, the integrated GWP of total annual CH4 and N2O emissions satisfies PF>>RR≈RW. The GWP of PF is higher than that of RW and RR by a factor of 2.6 and 2.7, respectively. Of the total GWP of CH4 and N2O emissions, CH4 emission contributed to 93%, 65% and 59% in PF, RW and RR, respectively. These results suggest that changing PF to RW and RR can substantially reduce not only CH4 emission but also the total GWP of the CH4 and N2O emissions.     

Long-Term Trends of Carbon Monoxide Total Columnar Amount in Urban Areas and Background Regions: Ground-and Satellite-based Spectroscopic Measurements

A comparative study was carried out to explore carbon monoxide total columnar amount(CO TC) in background and polluted atmosphere, including the stations of ZSS(Zvenigorod), ZOTTO(Central Siberia), Peterhof, Beijing, and Moscow,during 1998–2014, on the basis of ground-and satellite-based spectroscopic measurements. Interannual variations of CO TC in different regions of Eurasia were obtained from ground-based spectroscopic observations, combined with satellite data from the sensors MOPITT(2001–14), AIRS(2003–14), and IASI Met Op-A(2010–13). A decreasing trend in CO TC(1998–2014) was found at the urban site of Beijing, where CO TC decreased by 1.14% ± 0.87% yr~(-1). Meanwhile, at the Moscow site, CO TC decreased remarkably by 3.73% ± 0.39% yr~(-1). In the background regions(ZSS, ZOTTO, Peterhof), the reduction was 0.9%–1.7% yr~(-1) during the same period. Based on the AIRSv6 satellite data for the period 2003–14, a slight decrease(0.4%–0.6% yr~(-1)) of CO TC was detected over the midlatitudes of Eurasia, while a reduction of 0.9%–1.2% yr~(-1) was found in Southeast Asia. The degree of correlation between the CO TC derived from satellite products(MOPITTv6 Joint, AIRSv6 and IASI Met Op-A) and ground-based measurements was calculated, revealing significant correlation in unpolluted regions.While in polluted areas, IASI Met Op-A and AIRSv6 data underestimated CO TC by a factor of 1.5–2.8. On average, the correlation coefficient between ground-and satellite-based data increased significantly for cases with PBL heights greater than 500 m.     

Spatial Source Contributions Identification of Acid Rain over the Yangtze River Delta Using a Variety of Methods

The source-receptor relation of wet deposition has been a continuous issue in studies of regional environmental pollution over the past two decades.In the absence of direct observational evidence,the problem is difficult to solve—a topic of broad international debate since the turn of the present century.In the present study,a variety of methods focused on the sources of the wet deposition of acidic substances,like sulfate and nitrate,were used to investigate the precipitation chemistry over the Yangtze River Delta(YRD)during 2007.Back-trajectory analysis associated with the observation data and a source tracing method coupled with the Nested Air Quality Prediction Modeling System(NAQPMS)are proved to be effective methods for investigating the sources of wet deposition over the YRD.Comparison among the back-trajectory,footprint,and NAQPMS results shows good consistency,both qualitatively and quantitatively.The most important contributor to acidic substances in the YRD,as well as heavy acid rain over the region,is the anthropogenic pollution from East China,which accounts for more than 70%.     

Global Financial Crisis Making a V-Shaped Fluctuation in NO_2 Pollution over the Yangtze River Delta

The Yangtze River Delta(YRD),China’s main cultural and economic center,has become one of the most seriously polluted areas in the world with respect to nitrogen oxides(NO_x),owing to its rapid industrialization and urbanization,as well as substantial coal consumption.On the basis of nitrogen dioxide(NO_2)density data from ozone monitoring instrument(OMI)and ground-based observations,the effects of industrial fluctuations due to the financial crisis on local NO_2 pollution were quantitatively assessed.The results were as follows.(1)A distinct V-shaped fluctuation of major industrial products,thermal generating capacity,electricity consumption,and tropospheric NO_2 densities was associated with the global financial crisis from May 2007 to December 2009,with the largest anomalies 1.5 times more than standard deviations at the height of the crisis period from November 2008 to February 2009.(2)Among all industrial sectors,thermal power plants were mainly responsible for fluctuations in local NO_2 pollution during the crisis period.Thermal generating capacity had its greatest decrease of 12.10%at the height of the crisis compared with that during November 2007–February 2008,leading to local tropospheric NO_2 density decreasing by 16.97%.As the crisis appeased,thermal generating capacity increased by 29.63%from November 2009 to February 2010,and tropospheric NO_2 densities correspondingly increased by 30.07%.(3)Among all industrial sectors in the YRD,the thermal power sector has the greatest coal consumption of about 65.96%.A decline in thermal power of about 10% can induce a decrease of about 30%in NOx emissions and NO_2 densities,meaning that a relative small fluctuation in industrial production can lead to a large decrease in tropospheric NO_2 densities over industrially developed areas like the YRD region.Since electricity is mainly obtained from local coal-burning thermal plants without NO_x-processing equipment,installing NO_x-removal devices for all thermal power plants is an important and feasible way of controlling local NO_x pollution at present.     

Attribution of the Present-Day Aerosol Direct Radiative Forcing to Anthropogenic Emission Sectors

In this study,a general circulation model coupled with a gas-phase module and an aerosol chemistry module was employed to investigate the impacts of anthropogenic emission sectors on aerosol direct radiative forcing at the top of atmosphere(TOA)in the present-day climate.The predictions were based on the emission inventories developed in support of the Intergovernmental Panel on Climate Change(IPCC)Fifth Assessment Report(AR5).Six emission sectors—agriculture,open biomass burning,domestic activities,industry,energy generation,and transport—were considered,with a special focus on nitrate aerosol that shows large uncertainties in current models.The results show that the energy sector accounts for the largest contribution(-222 mW m 2)to global aerosol radiative forcing,with substantial negative forcing from sulfate.Inclusion of nitrate results in the transport sector yielding a global nitrate radiative forcing of-92 mW m-2and an internally mixed aerosol radiative forcing of -85 mW m-2,which is opposite to the positive radiative forcing predicted in the past,indicating that the transport emissions could not be a potential control target to counteract climate warming as expected before.The maximum change in nitrate burden is found to be associated with agricultural emissions,which accounts for about75%of global ammonia gas(NH3)emissions.Agricultural emissions account for global nitrate radiative forcing of -186 mW m-2and internally mixed aerosols direct radiative forcing of -149 mW m-2.Such agricultural radiative forcing exceeds the radiative forcing of the industrial sector and is responsible for a large portion of negative radiative forcing over the Northern Hemisphere.     

Probability distribution function of a forced passive tracer in the lower stratosphere

The probability distribution function （PDF） of a passive tracer, forced by a ＂mean gradient＂, is studied. First, we take two theoretical approaches, the Lagrangian and the conditional closure formalisms, to study the PDFs of such an externally forced passive tracer. Then, we carry out numerical simulations for an idealized random flow on a sphere and for European Center for Medium-Range Weather Forecasts （ECMWF） stratospheric winds to test whether the mean-gradient model can be applied to studying stratospheric tracer mixing in midlatitude surf zones, in which a weak and poleward zonal-mean gradient is maintained by tracer leakage through polar and tropical mixing barriers, and whether the PDFs of tracer fluctuations in midlatitudes are consistent with the theoretical predictions. The numerical simulations show that when diffusive dissipation is balanced by the mean-gradient forcing, the PDF in the random flow and the Southern-Hemisphere PDFs in ECMWF winds show time-invariant exponential tails, consistent with theoretical predictions. In the Northern Hemisphere, the PDFs exhibit non-Gaussian tails. However, the PDF tails are not consistent with theoretical expectations. The long-term behavior of the PDF tails of the forced tracer is compared to that of a decaying tracer. It is found that the PDF tails of the decaying tracer are time-dependent, and evolve toward flatter than exponential.     

Preface to the Special Issue on the Program of “Carbon Budget and Relevant Issues”—A Strategic Scientific Pioneering Program of the Chinese Academy of Sciences

<正>Global warming has been one of the biggest issues faced by the world in recent decades.It is closely related to anthropogenic emissions of greenhouse gases(GHGs)—mainly CO_2,CH_4 and N_2O—and the effects of reducing emissions and increasing the carbon fixation capability.China,as a large country with rapid economic and social development,has a major     

Particulate Amines in the Background Atmosphere of the Yangtze River Delta,China: Concentration,Size Distribution,and Sources

Amines are important for new particle formation and subsequent growth in the atmosphere. Consequently, the processes involved are receiving more attention in recent years. Here, we conduct a field observation in order to investigate the atmospheric particulate amines at a background site in the Yangtze River Delta(YRD) during the summer of 2018.Four amines in PM_(2.5), i.e., methylamine(MA), dimethylamine(DMA), diethylamine(DEA), and trimethylamine(TMA),were collected, twice daily and analyzed. During the campaign, our measurements found the concentrations of MA, DMA,DEA, and TMA of 15.0 ± 15.0, 6.3 ± 6.9, 20.4 ± 30.1, and 4.0 ± 5.9 ng m–3, respectively, and the four amines correlated well with each other. The concentration of amines appear to be independent of whether they were collected during the day or night. Both MA and DMA exhibited a bimodal size distribution that had peaks at 0.67 and 1.1 μm, suggesting amines preferably distribute on submicron particles. Boundary layer height(BLH), relative humidity, and pH of aerosols were found have a negative relationship with amines, while aerosol liquid water content(ALWC) was found to have a positive relationship with amines. The PMF(positive matrix factorization) source apportionment results showed that the main source of amines in Chongming Island was of anthropogenic origin such as industrial and biomass emission, followed by marine sources including sea salt and marine biogenic sources. Given that the YRD region is still suffering from complex atmospheric pollution and that the knowledge on aerosol amines is still limited, more field studies are in urgent need for a better understanding of the pollution characteristics of amines.     

Spatiotemporal Variations of Cloud Amount over the Yangtze River Delta, China

Based on the NOAA's Advanced Very High Resolution Radiometer(AVHRR) Pathfinder Atmospheres Extended(PATMOS-x) monthly mean cloud amount data, variations of annual and seasonal mean cloud amount over the Yangtze River Delta(YRD), China were examined for the period 1982–2006 by using a linear regression analysis. Both total and high-level cloud amounts peak in June and reach minimum in December, mid-level clouds have a peak during winter months and reach a minimum in summer, and lowlevel clouds vary weakly throughout the year with a weak maximum from August to October. For the annual mean cloud amount, a slightly decreasing tendency(–0.6% sky cover per decade) of total cloud amount is observed during the studying period, which is mainly due to the reduction of annual mean high-level cloud amount(–2.2% sky cover per decade). Mid-level clouds occur least(approximately 15% sky cover) and remain invariant, while the low-level cloud amount shows a significant increase during spring(1.5% sky cover per decade) and summer(3.0% sky cover per decade). Further analysis has revealed that the increased low-level clouds during the summer season are mainly impacted by the local environment. For example,compared to the low-level cloud amounts over the adjacent rural areas(e.g., cropland, large water body, and mountain areas covered by forest), those over and around urban agglomerations rise more dramatically.     

Tower-Based Greenhouse Gas Measurement Network Design——The National Institute of Standards and Technology North East Corridor Testbed

The North–East Corridor(NEC) Testbed project is the 3rd of three NIST(National Institute of Standards and Technology) greenhouse gas emissions testbeds designed to advance greenhouse gas measurements capabilities. A design approach for a dense observing network combined with atmospheric inversion methodologies is described. The Advanced Research Weather Research and Forecasting Model with the Stochastic Time-Inverted Lagrangian Transport model were used to derive the sensitivity of hypothetical observations to surface greenhouse gas emissions(footprints). Unlike other network design algorithms, an iterative selection algorithm, based on a k-means clustering method, was applied to minimize the similarities between the temporal response of each site and maximize sensitivity to the urban emissions contribution. Once a network was selected, a synthetic inversion Bayesian Kalman filter was used to evaluate observing system performance. We present the performances of various measurement network configurations consisting of differing numbers of towers and tower locations. Results show that an overly spatially compact network has decreased spatial coverage, as the spatial information added per site is then suboptimal as to cover the largest possible area, whilst networks dispersed too broadly lose capabilities of constraining flux uncertainties. In addition, we explore the possibility of using a very high density network of lower cost and performance sensors characterized by larger uncertainties and temporal drift. Analysis convergence is faster with a large number of observing locations, reducing the response time of the filter. Larger uncertainties in the observations implies lower values of uncertainty reduction. On the other hand, the drift is a bias in nature, which is added to the observations and,therefore, biasing the retrieved fluxes.     

Dominant Synoptic Patterns and Their Relationships with PM_(2.5) Pollution in Winter over the Beijing–Tianjin–Hebei and Yangtze River Delta Regions in China

This paper concerns about the episodes of PM_(2.5) pollution that frequently occur in China in winter months. The severity of PM_(2.5) pollution is strongly dependent on the synoptic-scale atmospheric conditions. We combined PM_(2.5) concentration data and meteorological data with the Hybrid Single Particle Lagrangian Integrated Trajectory model(HYSPLIT4) to investigate the dominant synoptic patterns and their relationships with PM_(2.5) pollution over the Beijing–Tianjin–Hebei(BTH) and Yangtze River Delta(YRD) regions in the winters of 2014–17. The transport of PM_(2.5) from the BTH to YRD regions was examined by using cluster analysis and HYSPLIT4. It is found that the level of PM_(2.5) pollution over the BTH region was higher than that over the YRD region. The concentration of PM_(2.5) in the atmosphere was more closely related to meteorological factors over the BTH region. The episodes of PM_(2.5) pollution over the BTH region in winter were related to weather patterns such as the rear of a high-pressure system approaching the sea, a high-pressure field, a saddle pressure field, and the leading edge of a cold front. By contrast,PM_(2.5) pollution episodes in the YRD region in winter were mainly associated with the external transport of cold air, a high-pressure field, and a uniform pressure field. Cluster analysis shows that the trajectories of PM_(2.5) were significantly different under different weather patterns. PM_(2.5) would be transported from the BTH to the YRD within 48 h when the PM_(2.5) pollution episodes were associated with three different kinds of weather patterns: the rear of a highpressure system approaching the sea, the high-pressure field, and the leading edge of a cold front over the BTH region. This suggests a possible method to predict PM_(2.5) pollution episodes based on synoptic-scale patterns.     

Cloud Condensation Nuclei over the Bay of Bengal during the Indian Summer Monsoon

The first measurements of cloud condensation nuclei(CCN) at five supersaturations were carried out onboard the research vessel "Sagar Kanya"(cruise SK-296) from the south to the head-bay of the Bay of Bengal as part of the Continental Tropical Convergence Zone(CTCZ) Project during the Indian summer monsoon of 2012. In this paper, we assess the diurnal variation in CCN distributions at supersaturations from 0.2% to 1%(in steps of 0.2%) and the power-law fit at supersaturation of 1%.The diurnal pattern shows peaks in CCN concentration(NCCN) at supersaturations from 0.2% to 1% between 0600 and 0700 LST(local standard time, UTC+0530), with relatively low concentrations between 1200 and 1400 LST, followed by a peak at around 1800 LST. The power-law fit for the CCN distribution at different supersaturation levels relates the empirical exponent(k) of supersaturation(%) and the NCCNat a supersaturation of 1%. The NCCNat a supersaturation of 0.4% is observed to vary from 702 cm~(-3) to 1289 cm~(-3), with a mean of 961 ± 161 cm~(-3)(95% confidence interval), representing the CCN activity of marine air masses. Whereas, the mean NCCNof 1628 ± 193 cm~(-3) at a supersaturation of 1% is higher than anticipated for the marine background. When the number of CCN spectra is 1293, the value of k is 0.57 ± 0.03(99% confidence interval)and its probability distribution shows cumulative counts significant at k ≈ 0.55 ± 0.25. The results are found to be better at representing the features of the marine environment(103 cm~(-3) and k ≈ 0.5) and useful for validating CCN closure studies for Indian sea regions.     

Source Contributions to PM_(2.5) under Unfavorable Weather Conditions in Guangzhou City,China

Historical haze episodes(2013–16) in Guangzhou were examined and classified according to synoptic weather systems.Four types of weather systems were found to be unfavorable, among which "foreside of a cold front"(FC) and "sea high pressure"(SP) were the most frequent( 75% of the total). Targeted case studies were conducted based on an FC-affected event and an SP-affected event with the aim of understanding the characteristics of the contributions of source regions to fine particulate matter(PM_(2.5)) in Guangzhou. Four kinds of contributions—namely, emissions outside Guangdong Province(super-region), emissions from the Pearl River Delta region(PRD region), emissions from Guangzhou–Foshan–Shenzhen(GFS region), and emissions from Guangzhou(local)—were investigated using the Weather Research and Forecasting–Community Multiscale Air Quality model. The results showed that the source region contribution differed with different weather systems. SP was a stagnant weather condition, and the source region contribution ratio showed that the local region was a major contributor(37%), while the PRD region, GFS region and the super-region only contributed 8%, 2.8% and 7%, respectively, to PM_(2.5) concentrations. By contrast, FC favored regional transport. The super-region became noticeable,contributing 34.8%, while the local region decreased to 12%. A simple method was proposed to quantify the relative impact of meteorology and emissions. Meteorology had a 35% impact, compared with an impact of-18% for emissions, when comparing the FC-affected event with that of the SP. The results from this study can provide guidance to policymakers for the implementation of effective control strategies.